The First Ten Years of the Heinrich Hertz Chair Endowed by ...

“Innovations are the fuel powering our future“
Address
Heinrich Hertz Chair of Deutsche Telekom AG
Prof. Dr. Karsten Buse
University of Bonn
Institute of Physics
Wegelerstraße 8
53115 Bonn
Germany
Contact
Phone: 0228/73-4898
Fax: 0228/73-4038
E-Mail: kbuse@uni-bonn.de
Web
http://www.photonik.uni-bonn.de
2000 - 2010 The First Ten Years of the Heinrich Hertz Chair Endowed by Deutsche Telekom AG
The First Ten Years of the Heinrich Hertz Chair
Endowed by Deutsche Telekom AG
2000 – 2010

Publishing Details
Realization
Editor
Prof. Dr. Karsten Buse
Layout, Graphics
Bosse und Meinhard Wissenschaftskommunikation
Print
Druckerei Brandt, Bonn
Photo credits
• Cover, 58: Lightline (www.lightline.de)
• 6, 12, 25, 42, 44 (right), 50, 60: Bosse und Meinhard
• 7: University of Bonn
• 8: Deutsche Telekom AG
• 9: Frank Homann, University of Bonn
• 10: wikipedia
• 11, 16, 18, 19, 27-41 (except 33 (right) and 41
(right)), 44 (left), 45, 51, 47, 48, 49, 55, 56, 57, 62:
Heinrich Hertz Chair
• 14, 20, 21: istockphoto
• 15: Crystal Technology Inc.
• 17: Nature Photonics
• 26: Ulrike E. Klopp, University of Bonn
• 33 (right): Thomas Ollendorf, Deutsche Telekom AG
• 41 (right): Fig. 2 of the article: “Continuous-wave
optical parametric terahertz source“ by R. Sowade,
I. Breunig, I. Camara Mayorga, J. Kiessling, C. Tulea,
V. Dierolf, and K. Buse, Optics Express, Vol. 17,
22303 (2009)
• 52: Harald Giessen, University of Stuttgart
• 53: T-Labs
• 61: Eric Lichtenscheidt
63

The First Ten Years of the Heinrich Hertz Chair
Endowed by Deutsche Telekom AG
2000 – 2010
Prof. Dr. Karsten Buse
Institute of Physics
University of Bonn
3

4
Content
Preface 6
Heinrich Hertz 10
Research & Innovations 12
Research: from the fundamental to the highly applied ............................................................ 14
The century of photonics ....................................................................................................... 14
Lithium niobate crystals: silicon of photonics ........................................................................ 15
Current research in the university labs ................................................................................... 15
Material research .................................................................................................................. 16
New applications ................................................................................................................... 18
Exemplary projects directly linked to needs of Deutsche Telekom AG ..................................... 19
Patents and patent applications ............................................................................................. 22
Timeline 2000 - today 25
Team 42
Current team ......................................................................................................................... 44
Theses accomplished at the Heinrich Hertz Chair of Deutsche Telekom AG 44

Alumni network ..................................................................................................................... 45
Careers ................................................................................................................................. 46
Cooperation .......................................................................................................................... 50
Deutsche Telekom Laboratories ............................................................................................. 53
National and international close cooperation partners............................................................ 54
Guest scientists ..................................................................................................................... 55
Entrepreneurship ................................................................................................................... 57
Outreach 58
Teaching................................................................................................................................ 60
University of Bonn – self-administration ................................................................................. 61
Events ................................................................................................................................... 62
Publishing Details 63
Realization ............................................................................................................................ 63
Photo credits ......................................................................................................................... 63
5

Preface

Preface
The University of Bonn is very proud of its cooperation
with Deutsche Telekom. The resulting Heinrich
Hertz Chair has proved a huge success over the first
decade of its existence.
There is a widespread misconception about university
research. It is often thought that the basic research
done in academic institutions rarely and only very
slowly leads to applications or products ready for the
market. According to this common prejudice, effective
applied science only takes place at places known as
technical universities or even universities of applied
science. Indeed, there is an underlying misconception
that basic research is far from exciting, contrary to
the applied sciences. However, a closer look quickly
reveals, of course, that there can be no applied science
without the solid groundwork of basic research.
The ten-year anniversary of Deutsche Telekom’s commitment
to the University of Bonn’s Heinrich Hertz
Chair is a perfect occasion for presenting a prime example
of highly successful research leading to important
applications. It certainly is no coincidence that
the chair was named after this great physicist, a man
whose research laid the groundwork for a plethora of
applications and products. Originally planned for a
period of only five years, the co-operation between the
University of Bonn and Deutsche Telekom proved so
successful that, in 2004, it was extended indefinitely.
Prof. Dr. Jürgen Fohrmann,
Rector of the University of Bonn
This collaboration has shown that the relationship
between these two rather different institutions
brings mutual benefits, with the university‘s top-level
research contributing directly and indirectly to the
success of Deutsche Telekom.
The ongoing commitment to this chair is testimony to
the excellent scientific work of its current holder, Professor
Dr. Karsten Buse, and his team as well as the
Institute of Physics as a whole. It certainly serves as
an example for other forms of co-operation between
the University of Bonn and outside institutions and
organizations, whether academic or non-academic.
We highly appreciate the fact that Deutsche Telekom
values the University of Bonn as a partner with whom
it actively seeks to co-operate and look forward to continuing
and deepening this relationship in the years to
come.
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Preface
Located on the campus of the Technical University of
Berlin, Deutsche Telekom Laboratories prove that Deutsche
Telekom’s strategy to link the worlds of academia
and industry is working. This is a viable approach to
building innovation leadership in the telecommunications
industry. The synergies generated here are fertilizing
both university research and product development in our
industry. Seven professors from areas of vital interest to
Deutsche Telekom, such as security, networks and usability,
have been appointed in Berlin. These professors,
along with more than 150 research scientists, post-docs
and students belonging to their groups, are working
desk-to-desk together with more than 180 Deutsche
Telekom experts.
But how does basic research on physics, lasers and
crystals conducted in Bonn fit into this picture? At
the Heinrich Hertz Chair, the researchers are not only
pursuing highly relevant specific developments and thus
generating intellectual properties, they are also providing
the broad underlying know-how on applied optics and
identifying – with their keen sense of upcoming technical
trends – the innovations that will radically transform the
telecommunications industry. One has to keep in mind
that optical technologies are crucial to the processes of
acquiring, transmitting and displaying information. In
fact, without optics there would be no fast Internet and
no modern communications at all!
Telekom Laboratories have been forging links between
the Heinrich Hertz Chair and the organizational units of
Deutsche Telekom. The expertise of the Heinrich Hertz
Peter Möckel,
Leiter Deutsche Telekom Laboratories
Chair in Bonn is accessed by Telekom Laboratories in
Berlin and made available to many of Deutsche Telekom’s
business units throughout the world. Suggestions
for innovation projects emerging from the Heinrich Hertz
Chair are evaluated in Berlin and have led in many cases
to successful R&D projects, product recommendations
and patents. Thus, an extremely encouraging and fruitful
collaboration has emerged. Among many other examples,
important breakthroughs have been made in the
fields of smart glasses, 3D entertainment and terahertz
technology. Another point I would like to emphasize is
that our collaboration with Professor Buse and his team
has been a real pleasure, characterized by open-minded,
serious, enthusiastic and dependable interaction. For
instance, requests from our side always meet with a very
fast, positive and competent response.
The University of Bonn and Deutsche Telekom certainly
made the right decision when they agreed this close
collaboration ten years ago. We appreciate the support
given by the University to the Heinrich Hertz Chair. This
makes us even more confident that we are investing in
the right team at the right place. The extraordinary innovations
that lie ahead of us will make our lives better. We
are happy to play an active role in this evolution as we
move forward into a new world with partners like those at
the Heinrich Hertz Chair of the University of Bonn.

Preface
The world is changing quickly, in academia as well as
in industry. The universities are facing severe challenges:
a total change of the curricula initiated by
the Bologna process, increased competition between
the best universities in Germany under the excellence
initiative, new arrangements for appointing academic
staff, plus more freedom and responsibility for the
individual universities. These reforms, introduced in
the last decade, go deeper and further than all the
reforms of the century before. The increased pace of
change is basically something very familiar to large
corporations. Deutsche Telekom was created from a
government institution and is now a flexible and innovative
business that competes successfully for market
share. This transition required a number of steps. The
company was overhauled to optimize its structures,
processes, human resources and finances.
Throughout this transition, one thing has, perhaps remarkably,
not changed: Deutsche Telekom‘s commitment
to its collaboration with the University of Bonn.
This partnership has endured, driven forward by the
wealth of ideas it generates. In this context, the Heinrich
Hertz Chair, which is affiliated with the Deutsche
Telekom Laboratories, has been particularly productive,
providing an effective bridge between academia
and industry. The resulting synergies provide very
good reasons for continuing our collaboration. After
all, ideas and innovations are the fuel that powers
academia as well as industry. And innovations created
at universities now find their way into real products
faster than ever.
Prof. Dr. Karsten Buse,
Holder of the Heinrich Hertz Chair endowed by Deutsche Telekom AG
In our fast-changing world, the know-how available at
universities is highly relevant to companies looking for
new markets and making sound investment decisions.
This booklet reviews our activities over the last ten
years, without claiming in any way to be a full account.
It shows how extensive the interaction between
the University of Bonn and Deutsche Telekom has
been, outlines the mutual benefits and illustrates our
capabilities.
The technological advances made in the last decade
are enormous. Mobile communication and the internet
have changed our ways of living and working. The
next decade will again be full of revolutionary changes
and innovations. Information technologies will play a
big role in helping us to conserve the natural environment;
we will experience mobile communication
with bandwidths of gigabits per second; and digital
holographic 3D displays will open a new dimension of
interaction. These are just a few examples. Each new
innovation opens up new opportunities – for academia
and industry. By coming together on the basis of
common interests to combine our expertise, we can
achieve a competitive edge and take maximum advantage
of the new breakthroughs. This is why we look
forward with such optimism to a bright future.
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Heinrich Hertz

Heinrich Hertz
Our namesake
The chair founded by Deutsche Telekom is named after
Heinrich Hertz, a famous physicist who worked at
the University of Bonn from 1889 until his early death
in 1894. Before coming to Bonn, Hertz had already
demonstrated the existence of electromagnetic waves
experimentally and proved the “Maxwell equations“
of electromagnetic theory. These equations are now
known as the basis of the description of all electrical
and magnetic phenomena. One fundamental parameter
of waves is their frequency, the number of oscillations
per second. Honoring Heinrich Hertz, this unit
is named after him (1 Hertz = 1 cycle per second).
Heinrich Hertz made important contributions also to
other fields. His discovery of the “photoelectric effect“,
the emission of electrons from metals illuminated
by short-wavelength light, was essential for the
development of quantum optics – a description of
“light“ complementary to wave optics.
Original equipment used by Heinrich Hertz at the Institute of
Physics: spark gap providing experimental evidence for the
existence of electromagnetic waves.
Heinrich Hertz also provides a good example how
fundamental knowledge can attain practical relevance.
He believed his research was purely academic in
nature, but Guglielmo Marconi quickly recognized that
the technology could be used for wireless communications.
A wireless telegraph service was established
across the Atlantic as early as 1907. These days,
innovations from research labs have the potential
of entirely changing our world just a few years later.
Indeed, the field of optics and solid state physics still
holds a wealth of important developments awaiting
discovery.
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Research and innovations
12

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Research and Innovations
Research: from the fundamental to the
highly applied
The last ten years have seen a number of successful
research projects. In the following, we shall review our
ongoing activities. In all cases, we sought patent protection
at a very early stage. Some specific projects
relate directly to the business needs of Deutsche
Telekom, often leading to advice or clear recommendations
for company decisions, including early
identification of potential breakthroughs.
A bunch of optical fibers - the key technology for worldwide
high-density and high-speed data transfer.
The century of photonics
All our projects involve know-how in the field of optics.
Modern optics, often called “photonics” in analogy
to electronics, is of great relevance for cutting-edge
science as well as for telecommunications. The 2009
Nobel Price for Physics offers a striking example:
Willard S. Boyle und George E. Smith were honored
for their work on digital cameras, which revolutionized
photography. Charles Kuen Kao also received the
2009 Prize, in his case for developing optical fibers
for data transmission. Both achievements were made
in the early 70s. Today, a dense optical-fiber network
encompasses the globe, forming the backbone of the
internet. Charles Kao recognized the full potential
of glass and realized that purified silica glass is so
transparent that it can transmit data over hundreds of
kilometers without the need for amplification.

Lithium niobate crystals:
silicon of photonics
Our scientific core competence lies in the field of
nonlinear-optical crystals. Here – like in the case of
the silica glass for fibers – purity and full control of
the material properties are the enablers of applications.
We are working in particular on the utilization
of lithium niobate crystals, a material that is already
widely used for frequency filters in mobile phones and
television systems as well as for electro-optical modulators
to put information into the optical waves in
fiber networks. This material has another fascinating
but not fully explored property that has great potential
for applications: It can change the color of light.
This does not mean simple filtering, as in colored
glass, where part of the light spectrum is thrown
away. Rather, lithium niobate crystals really can
change the color of a light beam and do so very efficiently.
Low-cost infrared laser light can be transformed into
the valuable visible laser light needed for compact
projectors. It is also possible to generate terahertz
light, opening up promising applications in high-bandwidth
mobile data transmission. These are just a few
examples. Just like microelectronics became possible
because of silicon technology, lithium niobate is often
called the “silicon of photonics“ since, in many cases,
it forms the basis for gaining full control of light.
Boules and wafers are our working material: lithium niobate
single crystals. (Copyright: Crystal Technology, Inc.)
Current research in the university labs
Our strategy is to combine advanced material
research with the exploration and demonstration of
entirely new applications of lithium niobate crystals.
About half of the team is working in each of these
two areas.
This research has led to a total of 116 publications
and 24 patents. Some patents have already been commercialized
through licenses, others have a very high
potential to find relevant applications, e.g. in nextgeneration
mobile communications.
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Material research

Material research
Lithium niobate crystals have a positively and a
negatively charged end. As a non-centro-symmetric
material, lithium niobate has some highly advantageous
properties. The direction of this polarity can be
spatially structured. Since each section with a homogeneous
polarity is called “domain”, this structuring
is known as “domain engineering“, i.e. the creation of
tailored structures for specific uses. When subjected
to intense illumination, light can excite the material
because the light field interacts with the domains. As
a consequence, each domain emits light.
The domain structure determines which color the
emitted light will have and what direction it will
travel in. Controlling the crystals‘ domain structure
is therefore of critical importance, but this can be
tough since the domain formation is very difficult.
Structured electrical fields exceeding 20 000 V/mm
are needed to reverse the domains. We are seeking to
develop smart methods for more refined domain control.
One line of research uses, for instance, ultraviolet
light.
The lithium niobate crystals have another feature that
can be either useful or disastrous for applications: the
photorefractive effect. The material is transparent for
visible light, but the crystals always and unavoidably
contain a small amount of transition metals like iron,
typically at levels of just several parts per million.
Since transition metals can occur in different valence
states, they can act as both electron sources and
electron traps. Iron occurs here in forms such as Fe 2+
and Fe 3+ . Light excites the electrons from the filled
traps (e.g. Fe 2+ ) into the conduction band. Since the
material is polar, the electrons are moved on and
trapped elsewhere by empty traps (e.g. Fe 3+ ). There
is a build-up of space-charge fields that can easily
reach 10 000 V/m. These fields change the refractive
index. This can be used to make, for instance, volume
holographic wavelength filters of the type needed in
optical telecommunication fiber networks as add-drop
filters.
The effect, however, leads to distortions in highintensity
laser beams, which limits the usefulness of
the crystals for changing the color of light. We have
therefore developed and patented various methods to
clean the crystals of their photo-excitable electrons.
One successful approach is an “optical brush“. Here,
a light beam combined with appropriate heating can
reduce the density of the photo-excitable electrons by
a factor of 10 000 or more.
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Effect of optical damage in lithium niobate crystals. The left
side shows a laser beam that passed through a cleaned crystal,
whereas the laser beam on the right was strongly distorted.
In many cases one would like to combine the favorable
properties of two very different materials. One possibility
is to create hybrid materials that contain two
or more composites. For this purpose we developed a
chemical route to synthesize lithium niobate nanocrystals
carefully doped with different elements. These
nanocrystals can be dispersed in various liquids and
polymers. It is then possible to orientate the nanoparticles
in external electrical fields. In this way, even
common materials like polymers are able to change
the color of light, possibly with an even better performance
than the pure crystal material itself. Another
line of research is the use of single nanocrystals as
the best possible probes for biological applications.
Since the nanocrystals are polar, a voltage between
two membranes will orient the particles – an effect
that is seen in the efficiency of color conversion. This
would be of relevance to neuron sciences and other
fields.
New applications
The understanding of materials leads to novel applications.
Our group has built several high-performance
optical parametrical oscillators. These are systems
in which the light of a pump laser is changed in
color in a precisely defined way over a wide range
of wavelengths. For this purpose, the crystals are
embedded in a resonator and the pump photons are
split into two parts, the signal and the idler light. The
signal light is trapped in the resonator and strongly
enhanced. Several Watts of pump power may lead to
more than 1000 W of circulating idler power. By this
means we have created tunable light sources that are
of relevance to applications such as in spectroscopics.
We have placed particular emphasis on the generation
of terahertz radiation. This frequency range is
between the microwave region, which can be accessed
by electronics, and the far-infrared region, which can
be reached by conventional optical means. Terahertz
radiation may be very useful in wireless local area
networks with access speeds exceeding 10 Gbit/s. Its
potential here derives from the high carrier frequency.
A serious problem has so far been posed by the generation
of continuous-wave narrow-band diffraction-limited
terahertz radiation. But we have recently found a
solution through the optical parametrical oscillators,
referred to above. By setting up two cascaded parametrical
oscillation processes, we have generated
terahertz radiation with powers exceeding the best
state-of-the-art results by a factor of a thousand.

Terahertz waves make the leaf-veins visible: The veins absorp
the THz waves stronger since they contain more water.
One critical question here is whether further integration
of nonlinear-optical devices enabling change in
the color of light is possible. To answer this, we study
the so-called “whispering gallery mode resonators“:
In St. Paul‘s Cathedral in London it was observed
that acoustic waves can migrate for long distances
in a gallery of circular shape. This becomes possible
through the multiple reflections of acoustic waves at
the cathedral‘s walls. “Whispers“ can be transmitted
over 50 meters or more. A similar mechanism can be
utilized in optics when light is trapped in discs due to
the “total internal reflection“ that lets light be carried
around the globe in optical fibers.
So we have been studying ways to reproduce these
properties in whispering gallery mode resonators
made of lithium niobate. One aim is to make miniaturized
lithium niobate terahertz generators. This
demands full control of the ferroelectric domains as
well as the photorefractive effect. In order to get a
high efficiency and gains, one idea would be to dope
the resonators with laser-active ions like erbium and
thus allow additional light amplification through optical
pumping. This offers a direct path to miniaturizing
our innovations and thus making them cheap and
portable.
Exemplary projects directly linked to
needs of Deutsche Telekom AG
Optics is highly relevant to the activities of Deutsche
Telekom. Optical sensors grab information, as in digital
cameras, for example. In mobile communications,
electromagnetic waves – light of invisible wavelengths
– are employed to transmit data. The fiber-networks
make high-bandwidth communication possible, with a
single fiber having the capacity to transmit in parallel
100 million telephone calls. Another aspect is optical
displays used to show information, either on a mobile
phone or on a large screen.
Further breakthroughs will be made over the next decade,
again changing our way of acquiring, transmitting
and receiving information. Each innovation offers
opportunities for a telecommunications provider. At
an early stage of development, the relevant knowhow
is brought into the various divisions of Deutsche
Telekom and shared in workshops where the crossconnections
can be made. Ideas formulated in these
workshops are then patent-protected and action
strategies are developed. Finally, a business unit has
to decide whether the new technology will be utilized
and given priority.
It is not an easy matter to evaluate the impact of this
cooperation, but our team at the University of Bonn
has contributed to projects with unquestionable commercial
benefits for Deutsche Telekom, certainly in
excess of € 100 millions in 2010.
In the following, we shall describe three of the many
fields of cooperation.
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3D entertainment
The movie Avatar surpassed the one-billion-revenue
threshold in just 17 days after its release. This is an
all-time record. The film‘s special appeal comes from
the advanced 3D technology that has been installed
in many cinemas over the last two years. So far this
technology is not available for the home viewing, but
it is only a matter of time until 3D entertainment
will enter our living rooms. Suitable displays are the
technological enabler here, and the relevant standards
were approved in late 2009. So the race is now on
to make IP TV 3D-ready, along with its many other
advantages.
For the first display generations, viewers will have
to wear special glasses with polarizers or shutter
technology. On a longer time-scale, it will be digital
holography that provides the ultimate 3D experience.
This, however, demands very large bandwidths and
computing power. 3D entertainment will become a
very popular and exciting field that will again change
the way we live and work.
Training at schools and universities, advertisements,
technical consultancy and many other fields will be influenced
by the availability of this full 3D technology.

Communication through optical fibers requires sophisticated
optical control centers.
Terahertz communications
The frequency of a data carrier determines the
bandwidth. Everyone knows this from radio receivers,
where the very high frequency band (VHF) has a much
better quality than the bands with longer wavelengths
and thus lower frequencies. The extreme transmission
capacity of optical fibers also derives from the high
frequency of optical waves.
Mobile communication has so far worked in the
gigahertz range. Thousand-times higher frequencies,
terahertz waves, would promise higher data rates,
but until recently no useful transmitters and receivers
were available. This will change as R&D is driven
by various technology demands, not least by the
applications in the security field, which also desires
waves of the same frequency. Mobile communications
bandwidths exceeding 10 Gbit/s are feasible and will,
in future, allow whole movies to be downloaded within
seconds.
Out-of-home media
Advertising and signage is becoming ever more digital.
Printed paper walls will be replaced step-by-step
by digital walls. This will increase flexibility and boost
revenues substantially. And adverts can be more local
und targeted. Digital advertising can be combined
with other telecommunication services to provide direct
information about the success of the placements
and exchange information with the valued customers.
Although Deutsche Telekom didn‘t use to be active
in the traditional out-door advertisement market, its
“Out-of-home media“ division recognized the trend
toward digitization a few years ago, responded flexibly
and is already achieving considerable success.
Contracts are made with cities, airports, arenas and
shopping malls. Deutsche Telekom provides all the
hardware needed and receives the right to use part of
the display time for placing ads. It is essential here to
choose the right display technology, also from an environmental
perspective with regard to power consumption.
Digital full-color paper would be ideal, but a lot
of R&D is still needed on this.
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Patents and patent applications
A number of patents have now been registered
worldwide.
26. “Multiple-View“-Informationsdisplayanordnung
with Ralph Michaels
DE 10 2008 028 634 (2008)
25. Drahtlose Datenübertragung mit Terahertz-
Wellen
with Ingo Breunig, Hans Joachim Einsiedler,
Gerhard Kadel, Jens Kießling, Bastian
Knabe, Josef Kraus, Ralph Michaels, Klaus
Milczewsky, Thomas Moersdorf, Michael
Neumann, and Rosita Sowade
DE 10 2008 020 466 (2008)
24. Verfahren zur Kontrolle elektromagnetischer
Terahertz-Trägerwellen
with Ingo Breunig, Hans Joachim Einsiedler,
Gerhard Kadel, Jens Kießling, Bastian
Knabe, Josef Kraus, Ralph Michaels, Klaus
Milczewsky, Michael Neumann and Rosita
Sowade
DE 10 2008 020 795 (2008)
23. Verfahren zur Erzeugung elektromagnetischer
Terahertz-Trägerwellen
with Ingo Breunig, Jens Kießling, Bastian
Knabe and Rosita Sowade
DE 10 2008 015 397 (2008)
22. Verfahren und Vorrichtung zur Verarbeitung
von Terahertz-Wellen
with Ingo Breunig, Jens Kießling, Bastian
Knabe and Rosita Sowade
DE 10 2008 019 010 (2008)
21. Hybridgepumpter optisch-parametrischer
Oszillator
with Ingo Breunig, Jens Kießling, Bastian
Knabe and Rosita Sowade
DE 10 2008 004 897 (2008)
20. Optische Reinigung nichtlinear-optischer
Kristalle
with Daniel Haertle, Matthias Falk and
Michael Kösters
DE 10 2007 004 400 (2007)
19. Method and apparatus for implementing a
multi-channel tunable filter
with Demetri Psaltis, Christophe Moser,
Greg Steckman, Ingo Nee and Jörg
Hukriede
US Patent 7,483,190 (2006)

18. Behandlung von Kristallen zur Vermeidung
optischen Schadens
with Matthias Falk and Theo Woike
DE 10 2006 016 201 (2006)
17. Holographic pump coupler and laser grating
reflector
with Christophe Moser and Demetri Psaltis
US Patent 7,542,639 (2005)
16. Behandlung von Kristallen zur Vermeidung
lichtinduzierter Änderungen des Brechungsindex
with Matthias Falk and Konrad Peithmann
DE 10 2004 002 109 (2004)
15. Method and apparatus for implementing a
multi-channel tunable filter
with Demetri Psaltis, Christophe Moser,
Greg Steckman, Ingo Nee and Jörg
Hukriede
US Patent 7,136,206 (2004)
14. Effiziente nichtlinear-optische Polymere mit
großer Polarisierungsstabilität
with Nils Benter, Horst Berneth, Ralph Bertram,
Rainer Hagen, Serguei Kostromine,
Ákos Hoffmann and Elisabeth Soergel
DE 101 47 724 and DE 102 29 779 (2003)
13. Photorefraktive Lithographie
with Birk Andreas and Konrad Peithmann
DE 103 264 29 (2003)
12. Nichtlineare Erhöhung der Photosensitivität
photorefraktiver Kristalle
with Marc Luennemann
DE 101 375 50 (2003)
11. Röntgensensor
with Birk Andreas and Dirk Berben
DE 101 246 61 (2003)
10. Erhöhung der Resistenz von Kristallen gegen
optischen Schaden
with Manfred Müller and Jörg Hukriede
DE 103 000 80 (2002)
9. Optischer Detektor mit räumlicher Auflösung
im Nanometer-Bereich
with Ákos Hoffmann, Jürg Hulliger and
Elisabeth Soergel
DE 102 219 70 (2002)
8. Integrated optical wavelength division multiplexing
using a bench of channel waveguides
with Demetri Psaltis, Christophe Moser,
Greg Steckman, Ingo Nee and Jörg
Hukriede
US Patent application 20020090171A1
(2001)
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7. Photorefraktiver Röntgensensor
with Birk Andreas and Dirk Berben
DE 101 246 61 (2001)
6. Tunable holographic drop filter with quasi
phase-conjugate fiber coupling
with Demetri Psaltis, Christophe Moser,
Greg Steckman, Ingo Nee, Jörg Hukriede
and Joseph W. Goodman
US Patent 6,987,907 (2001)
5. Tunable holographic filter
with Demetri Psaltis
US Patent 6,844,946 (2001)
4. Method and apparatus for implementing a
multi-channel tunable filter
with Demetri Psaltis, Christophe Moser,
Greg Steckman, Ingo Nee and Jörg
Hukriede
US Patent 6,829,067 (2001)
3. Verfahren und Vorrichtung zur Analyse und
Aufzeichnung von Lichtwellen
DE 199 190 20 (2001)
2. Non-volatile holographic storage in doublydoped
photorefractive material
with Ali Adibi and Demetri Psaltis
US 6,157,470 (1999)
1. Röntgenbild-Erfassungssystem
DE 199 167 08 (1998)

Timeline 2000-today
25

26
2000
Publications
2000
K. Peithmann, J. Hukriede, K. Buse, E. Krätzig “Photorefractive properties
of lithium niobate volume crystals doped by copper diffusion”
Phys. Rev. B 61, 4615-4620 (2000)
D. Berben, K. Buse, S. Wevering, P. Herth, M. Imlau, Th. Woike “Lifetime
of small polarons in iron-doped lithium-niobate crystals” J. Appl.
Phys. 87, 1034-1041 (2000)
X. Yue, A. Adibi, T. Hudson, K. Buse, D. Psaltis “Role of cerium in lithium
niobate for holographic recording” J. Appl. Phys. 87, 4051-4055 (2000)
In March 2000 Karsten Buse was appointed
as a professor at the Rheinische Friedrich
Wilhelms University of Bonn. He received the
Heinrich Hertz Chair endowed by Deutsche
Telekom (from left to right: Joachim Klaus
[Deutsche Telekom AG], Prof. Dr. Karsten
Buse, Prof. Dr. Klaus Borchard [rector of the
University of Bonn, 1997-2004]).
K. Peithmann, A. Wiebrock, K. Buse, E. Krätzig “Low-spatial-frequency
refractive-index changes in iron-doped lithium-niobate crystals upon
illumination with a focused cw laser beam” J. Opt. Soc. Am. B 17, 586-
592 (2000)
I. Nee, M. Müller, K. Buse “Role of iron in lithium-niobate crystals for the
dark-storage-time of holograms” J. Appl. Phys. 88, 4282-4286 (2000)
H. Veenhuis, T. Börger, K. Peithmann, M. Flaspöhler, K. Buse,
R. Pankrath, H. Hesse, E. Krätzig “Light-induced charge transport
properties of photorefractive barium-calcium-titanate crystals doped with
rhodium” Appl. Phys. B 70, 797-801 (2000)
A. Adibi, K. Buse, D. Psaltis “Sensitivity improvement in two-center
holographic recording” Opt. Lett. 25, 539-541 (2000)

In 2000 the start-up company Ondax
Inc., located in Monrovia, California,
was founded together with colleagues
from the California Institute of
Technology. It produces, for instance,
volume holographic gratings that can
filter light in optical networks using
dense wavelength multiplexing.
H. Veenhuis, T. Börger, K. Buse, C. Kuper, H. Hesse, E. Krätzig “Lightinduced
charge-transport properties of photorefractive barium-calciumtitanate
crystals doped with iron” J. Appl. Phys. 88, 1042-1049 (2000)
K. Peithmann, N. Korneev, M. Flaspöhler, K. Buse, E. Krätzig “Investigation
of small polarons in reduced iron-doped lithium-niobate crystals
by non-steady-state photocurrent techniques” phys. stat. sol. (a) 178,
R1-R3 (2000)
K. Buse, M. Luennemann “3D imaging: wave front sensing utilizing a
birefringent crystal” Phys. Rev. Lett. 85, 3385-3387 (2000)
2001
I. Nee, M. Müller, K. Buse “Development of thermally fixed photorefractive
holograms without light“ Appl. Phys. B 72, 195-200 (2001)
Research laboratories and offices
were renovated to fit our needs. In
some cases we also got “hands on“ in
order to speed up the construction.
A. Adibi, K. Buse, D. Psaltis “Theoretical analysis of two-step holographic
recording with high-intensity pulses“ Phys. Rev. A 63, 3813-3829
(2001)
D. Berben, B. Andreas, K. Buse “X-ray-induced photochromic effects
in copper-doped lithium-niobate crystals” Appl. Phys. B 72, 729-732
(2001)
T. Woike, D. Berben, M. Imlau, K. Buse, R. Pankrath, E. Krätzig “Lifetime
of small polarons in strontium-barium-niobate crystals doped with cerium
or chromium” J. Appl. Phys. 89, 5663-5666 (2001)
A. Adibi, K. Buse, D. Psaltis “The role of carrier mobility in holographic
recording in LiNbO 3 ” Appl. Phys. B 72, 653-659 (2001)
27

2001
28
We moved into the newly
renovated offices and labs.
A. Adibi, K. Buse, D. Psaltis “Two-center holographic recording” J. Opt.
Soc. Am. B 18, 584-601 (2001)
Y. Yang, I. Nee, K. Buse, D. Psaltis “Ionic and electronic dark decay
of holograms in LiNbO 3 :Fe crystals” Appl. Phys. Lett. 78, 4076-4078
(2001)
N. Korneev, H. Veenhuis, K. Buse, E. Krätzig “Thermal fixing of holograms
and their electrically assisted development in barium-calciumtitanate
crystals” J. Opt. Soc. Am. B 18, 1570-1577 (2001)
H. Vogt, K. Buse, H. Hesse, E. Krätzig, R. R. García “Growth and holographic
characterization of nonstoichiometric sillenite-type crystals”
J. Appl. Phys. 90, 3167-3173 (2001)
A novel sensor for complete analysis
and recording of wavefronts was
developed and tested.
A. Adibi, K. Buse, D. Psaltis “System measure for persistence in holographic
recording and application to singly- and doubly-doped lithium
niobate” Appl. Opt. 40, 5175-5182 (2001)
2002
Y. Yang, K. Buse, D. Psaltis “Photorefractive recording in
LiNbO 3 :Mn” Opt. Lett. 27, 158-160 (2002)
M. Mützel, S. Tandler, D. Haubrich, D. Meschede, K. Peithmann,
M. Flaspöhler, K. Buse “Atom lithography with a holographic light mask”
Phys. Rev. Lett. 88, 083601/1–4 (2002)
K. Peithmann, K. Buse, E. Krätzig “Dark conductivity in copper-doped
lithium-niobate crystals“ Appl. Phys. B 74, 549-552 (2002)

Electro-optic modulators that are
based on electro-optic polymers were
fabricated in cooperation with the
Bayer AG.
G. Panotopoulos, M. Luennemann, K. Buse, D. Psaltis “Temperature
dependence of absorption in photorefractive iron-doped lithium niobate
crystals” J. Appl. Phys. 92, 793-796 (2002)
N. Korneev, O. Flores Ramirez, R. P. Bertram, N. Benter, E. Soergel,
K. Buse, R. Hagen, S. G. Kostromine “Pyroelectric properties of electrically
poled photo-addressable polymers“ J. Appl. Phys. 92, 1500-1503
(2002)
D. Berben, B. Andreas, K. Buse “Photorefractive X-ray imaging“ Appl.
Phys. Lett. 81, 1567-1569 (2002)
2002
2003
Poled lithium niobate crystal: The direction of
the c-axis was inverted in a predefined area.
In the region with the cross-like structure, the
former direction of polarization is preserved.
Such structures are useful for the generation
of light.
O. Beyer, I. Nee, F. Havermeyer, K. Buse “Holographic recording of
Bragg gratings for wavelength division multiplexing in doped and partially
polymerized polymethylmethacrylate” Appl. Opt. 42, 30-37 (2003)
K. Buse, E. Soergel “Holographie in Wissenschaft und Technik” Physik
Journal 2, 337-343 (2003)
Ch. Bäumer, D. Berben, K. Buse, H. Hesse, J. Imbrock “Determination
of the composition of lithium tantalate crystals by zero-birefringence
measurements” Appl. Phys. Lett. 82, 2248-2250 (2003)
M. Luennemann, U. Hartwig, G. Panotopoulos, K. Buse “Electro-optic
properties of lithium niobate crystals for extremely high external electric
fields” Appl. Phys. B 76, 403-406 (2003)
29

30
Filter characteristics of a holographic
grating in Plexiglas. The grating
has a diffraction efficiency of 99.5%
and a full-width-at-half-maximum of
approx. 1 nm. Such filters can be of
relevance for fiber-optical telecommunications
networks and low-cost
fiber-to-the-home solutions.
M. C. Wengler, M. Müller, E. Soergel, K. Buse “Poling dynamics of
lithium niobate crystals” Appl. Phys. B 76, 393-396 (2003)
Y. Yang, D. Psaltis, M. Luennemann, D. Berben, U. Hartwig,
K. Buse “Photorefractive properties of lithium niobate crystals doped with
manganese“ J. Opt. Soc. Am. B 20, 1491-1502 (2003)
M. Luennemann, U. Hartwig, K. Buse “Improvements of sensitivity and
refractive-index changes in photorefractive iron-doped lithium-niobate
crystals by application of extremely large external electrical fields” J. Opt.
Soc. Am. B 20, 1643-1648 (2003)
B. Andreas, K. Peithmann, E. Soergel, K. Buse “Photorefractive lithography
with synchrotron light in poly(methyl methacrylate) (PMMA)“, Appl.
Phys. Lett. 83, 1116-1118 (2003)
X-ray image of a test mask
recorded with a novel highly
resolving image converter.
The distance of the thinnest
lines in the right part of the
image is 25 µm.
Giant values of the refractive index
changes in photorefractive lithium
niobate upon the presence of external
electric fields. A high-voltage amplifier
allows to apply 60 000 V/mm to
the crystals. The index modulations
can be used for optical filters and optical
switches.
D. Berben, B. Sturman, A. A. Freschi, K. Buse “X-ray-induced conductivity
in iron-doped lithium-niobate crystals“ Phys. Rev. B 68, 035120/1-4
(2003)
I. Nee, O. Beyer, M. Müller, K. Buse “Multi-channel wavelength-divisionmultiplexing
with thermally-fixed Bragg gratings in photorefractive
lithium-niobate crystals“ J. Opt. Soc. Am. B 20, 1593-1602 (2003)
M. Mützel, U. Rasbach, D. Meschede, C. Burstedde, J. Braun, A. Kunoth,
K. Peithmann, K. Buse “Atomic nanofabrication with complex light
fields“ Appl. Phys. B 77, 1-9 (2003)
M. Müller, E. Soergel, K. Buse “Influence of UV illumination on the poling
characteristics of lithium niobate crystals“ Appl. Phys. Lett. 83, 1824-
1826 (2003)

2003
Finally!
Labs and offices in the second
section (basement in
the Wegelerstraße 10) are
ready to be equipped.
M. Gorkunov, B. Sturman, M. Luennemann, K. Buse “Feedback-controlled
two-wave coupling in reflection geometry: application to lithium niobate
crystals subjected to extremely high external electric fields“ Appl.
Phys. B 77, 43-48 (2003)
R. P. Bertram, E. Soergel, H. Blank, N. Benter, K. Buse, R. Hagen,
S. G. Kostromine “Strong electro-optic effect in electrically-poled photoaddressable
polymers“ J. Appl. Phys. 94, 6208-6211 (2003)
M. Luennemann, K. Buse, B. Sturman “Coupling effects for counterpropagating
light beams in lithium niobate crystals studied by grating
translation technique for extremely high external electric fields“ J. Appl.
Phys. 94, 6274-6279 (2003)
M. Müller, E. Soergel, K. Buse “Visualization of ferroelectric domains with
coherent light“ Opt. Lett. 28, 2515-2517 (2003)
Integrated-optical
waveguide made
of Plexiglas,
fabricated with
synchrotron radiation
from the local
electron accelerator
in the Institute
of Physics.
Magnesium-doped lithium niobate:
The photorefactive material is intensively
investigated since it is ideally
suited for high-density holographic
data storage using blue light. Oxidizing
improves the performance of the
material.
E. Soergel, R. Pankrath, K. Buse “Investigation of photorefractive SBN
crystals with atomic force microscopy“ Ferroelectrics 296, 19-27
(2003)
2004
M. Müller, E. Soergel, M. C. Wengler, K. Buse “Light deflection from
ferroelectric domain boundaries“ Appl. Phys. B 78, 367-370 (2004)
B. Andreas, K. Peithmann, K. Maier, K. Buse “Modification of the refractive
index of lithium niobate crystals by transmission of high-energy
4He 2+ and D + particles“ Appl. Phys. Lett. 84, 3813-3815 (2004)
M. C. Wengler, B. Schreder, E. Soergel, J. Zimmer, K. Buse “Spectral
photosensitivity and holographic performance of europium-doped fluorophosphate
glass” Appl. Phys. B 79, 597-601 (2004)
31

32
Domain pattern of a lithium niobate
crystal generated by UV-illumination.
Tailored domain patterns are needed
for efficient frequency conversion of
light, i.e., the generation of brilliant
light at any color wanted.
2004
M. C. Wengler, B. Fassbender, E. Soergel, K. Buse “Impact of ultraviolet light
on coercive field, poling dynamics and poling quality of various lithium niobate
crystals from different sources” J. Appl. Phys. 96, 2816-2820 (2004)
H. A. Eggert, B. Hecking, K. Buse “Electrical fixing in near-stoichiometric
lithium niobate crystals” Opt. Lett. 29, 2476-2478 (2004)
R. P. Bertram, N. Benter, D. Apitz, E. Soergel, K. Buse, R. Hagen,
S. G. Kostromine “Increased thermal stability of a poled electro-optic
polymer using high-molar-mass fractions” Phys. Rev. E 70, 041802/1-5
(2004)
A. Shumelyuk, K. Shcherbin, S. Odoulov, B. Sturman, E. Podivilov,
K. Buse “Slowing-down of light in photorefractive crystals with beam
intensity coupling reduced to zero” Phys. Rev. Lett. 93, 243604/1–4
(2004)
As advertisement for an
event we sent a laser beam
across Bonn and the Rhineland.
It has been recognized
still 100 km away from
Bonn, although the light
power was just 20 W. This
demonstrates impressively
the brilliance of laser light.
Light deflection at ferroelectric
domain boundaries:
A novel deflection effect
allows visualization of the
domain patterns during their
generation. This enables
faster development of suitable
domain-structuring
technologies.
M. Müller, E. Soergel, K. Buse “Light deflection from ferroelectric domain
structures in congruently melting lithium tantalate crystals”, Appl. Opt.
43, 6344-6347 (2004)
2005
U. Hartwig, K. Peithmann, B. Sturman, K. Buse “Strong permanent
reversible diffraction gratings in copper-doped lithium niobate crystals
caused by a zero-electric-field photorefractive effect” Appl. Phys. B 80,
227-230 (2005)
M. Müller, C. Langrock, E. Soergel, K. Buse, M. M. Fejer “Investigation
of periodically-poled lithium niobate crystals by light diffraction” J. Appl.
Phys. 97, 044102/1-4 (2005)

A 1-mm-thick lithium niobate crystal
during the transformation of iron in
the valence state 2+ (bottom, brownish)
into iron in the valence state 3+
(top, transparent). The treatment
allows adjusting of the strength of the
photorefractive effect in a very wide
range. In particular the transparent,
cleaned regions are useful for
nonlinear-optical applications where
the crystal changes the color of light.
C. L. Sones, M. C. Wengler, C. E. Valdivia, S. Mailis, R. W. Eason,
K. Buse “Light-induced order-of-magnitude decrease in the electric field
for domain nucleation in MgO-doped lithium niobate crystals” Appl.
Phys. Lett. 86, 212901/1-3 (2005)
O. Beyer, D. Maxein, K. Buse, B. Sturman, H. T. Hsieh, D. Psaltis “Femtosecond
time-resolved absorption processes in lithium niobate crystals”
Opt. Lett. 30, 1366-1368 (2005)
O. Beyer, D. Maxein, K. Buse, B. Sturman, H. T. Hsieh, D. Psaltis “Investigation
of nonlinear absorption processes with femtosecond light pulses
in lithium niobate crystals” Phys. Rev. E 71, 056603/1-8 (2005)
M. Koesters, H. Hsieh, D. Psaltis, K. Buse “Holography in commercially
available photo-etchable glasses” Appl. Opt. 44, 3399-3402 (2005)
Deutsche Telekom and the University of Bonn
continue their successful collaboration.
Ralph Michaels (Deutsche Telekom AG), Dr.
Reinhardt Lutz (Chancelor of the University of
Bonn), Prof. Dr. Karsten Buse (Holder of the
endowed chair ), Hans Albert Aukes (Deutsche
Telekom AG) und Prof. Dr. Klaus Borchard
(Rector of the University of Bonn from 1997-
2004).
(from left to right)
H. T. Hsieh, D. Psaltis, O. Beyer, D. Maxein, K. Buse, B. Sturman “Enhanced
temporal resolution in femtosecond dynamic-grating experiments”
J. Appl. Phys. 97, 113107/1-5 (2005)
B. Andreas, I. Breunig, K. Buse “Modeling of X-ray-induced refractiveindex
changes in poly (methyl methacrylate)” ChemPhysChem 6,
1544-1553 (2005)
H. T. Hsieh, D. Psaltis, O. Beyer, D. Maxein, C. v. Korff Schmising,
K. Buse, B. Sturman “Femtosecond holography in lithium niobate crystals”
Opt. Lett. 30, 2233-2235 (2005)
33

2005
34
Interferogram of a lithium niobate
crystal after treatment with highenergy
He ions. Irradiation resulted
in a change of the refractive index,
as it is clearly visible in the central,
irradiated area. Structuring of materials
by this method may lead, e.g., to
optical waveguides or other photonic
structures.
D. Apitz, R. P. Bertram, N. Benter, W. Hieringer, J. W. Andreasen,
M. M. Nielsen, P. M. Johansen, K. Buse “Investigation of chromophorechromophore
interaction by electro-optic measurements, linear dichroism,
X-ray scattering and density-functional calculations” Phys. Rev. E
72, 036610/1-10 (2005)
M. C. Wengler, U. Heinemeyer, E. Soergel, K. Buse “UV-assisted domain
inversion in magnesium-doped lithium niobate crystals” J. Appl. Phys.
98, 064104/1-7 (2005)
N. Benter, R. P. Bertram, E. Soergel, K. Buse, D. Apitz, L. Bang Jacobsen,
P. M. Johansen “Large-area Fabry-Pérot modulator based on electrooptic
polymers” Appl. Opt. 44, 6235-6239 (2005)
Transmission of fs light pulses of the wavelength
388 nm (photon energy 3.2 eV) through lithium
niobate crystals plotted versus the absorption
parameter, the product of the two-photon-absorption
coefficient, the light intensity and the crystal
thickness. The transition is shown schematically
in a band diagram (VB, valence band; LB, conduction
band). The material might be of interest
for manipulation of ultrashort laser pulses, being
as short as 0.000 000 000 001 seconds.
H. A. Eggert, F. Kalkum, B. Hecking, K. Buse “Optimization of electrical
fixing in near-stoichiometric iron-doped lithium niobate crystals” J. Opt.
Soc. Am. B 22, 2553–2559 (2005)
M. C. Falk, K. Buse “Thermo-electric method for nearly complete oxidization
of highly iron-doped lithium niobate crystals”, Appl. Phys. B 81,
853-855 (2005)
2006
K. Peithmann, M. R. Zamani Meymian, M. Haaks, K. Maier, B. Andreas,
K. Buse, H. Modrow “Fabrication of embedded waveguides in lithiumniobate
crystals by radiation damage” Appl. Phys. B 82, 419-422
(2006)

Diffraction efficiency of a holographic
grating versus read-out wavelength.
Dashed line: contribution of an absorption
grating. Dotted line: contribution
of the refractive index grating
which evolves from the absorption
grating due to the Kramers-Kronig
relationship. Solid line: Sum of both
effects: A new approach to get strong
non-electro-optic gratings for photonic
applications has been discovered.
J. R. Adleman, H. A. Eggert, K. Buse, D. Psaltis “Holographic grating
formation in a colloidal suspension of silver nanoparticles” Opt. Lett. 31,
447-449 (2006)
D. Nau, R. P. Bertram, K. Buse, T. Zentgraf, J. Kuhl, S. G. Tikhodeev,
N. A. Gippius, H. Giessen “Optical switching in metallic photonic
crystal slabs with photo-addressable polymers” Appl. Phys. B 82, 543-
547 (2006)
O. Beyer, I. Breunig, F. Kalkum, K. Buse “Photorefractive effect in irondoped
lithium niobate crystals induced by femtosecond pulses of 1.5 µm
wavelength” Appl. Phys. Lett. 88, 051120/1-3 (2006)
D. Apitz, R. P. Bertram, N. Benter, P. Sommer-Larsen, P. M. Johansen,
K. Buse “Conductivity of oriented bis-azo polymer films“ ChemPhysChem
7, 468-474 (2006)
2006
Photon splitting: Optical parametric
oscillator (pump beam: 1030 nm,
17 W, signal beam: 1470 nm, idler
beam: 3440 nm, 1.8 W). The nonlinear
material is periodically poled
lithium niobate. Additionally, various
lines of visible light are created by
sum frequency mixing.
U. Hartwig, M. Kösters, Th. Woike, K. Buse, S. Shumelyuk, S. Odoulov
“Frequency mixing of photorefractive and ferroelectric gratings in
lithium niobate crystals” Opt. Lett. 31, 583-585 (2006)
H. A. Eggert, F. Kalkum, K. Buse, B. Sturman “Bragg selectivity of spacecharge
gratings in multidomain lithium niobate crystals“ Opt. Lett. 31,
1256-1258 (2006)
A. Shumelyuk, U. Hartwig, K. Buse, S. Odoulov, Th. Woike “Linearity
of index grating recording with spatially oscillating photovoltaic currents”
J. Opt. Soc. Am. B 23, 857-860 (2006)
M. Kösters, U. Hartwig, Th. Woike, K. Buse, B. Sturman “Quantitative
characterization of periodically poled lithium niobate by electrically
induced Bragg diffraction” Appl. Phys. Lett. 88, 182910/1-3 (2006)
35

36
Frequency mixing of domain
gratings with photorefractive
gratings (a) leading to
additional light-diffraction
orders (b).
O. Beyer, D. Maxein, Th. Woike, K. Buse “Generation of small bound polarons
in lithium niobate crystals on the subpicosecond time scale” Appl.
Phys. B 83, 527-530 (2006)
Kh. Olimov, M. Falk, K. Buse, Th. Woike, J. Hormes, H. Modrow “X-ray
absorption near edge spectroscopy investigations of valency and lattice
occupation site of Fe in highly iron-doped lithium niobate crystals”
J. Phys. Condens. Matter 18, 5135-5146 (2006)
O. Beyer, C. von Korff Schmising, M. Luennemann, K. Buse, B. Sturman
“Long-living currents induced by nanosecond light pulses in LiNbO 3
crystals” Optics Express 14, 1533-1540 (2006)
U. Hartwig, K. Peithmann, Th. Woike, K. Buse “Determination of the
absorption cross section of dopants in lithium niobate crystals” J. Phys.:
Condens. Matter 18, L447-L450 (2006)
All-optical switching: A red light beam propagates
through a suspension of silver nano
particles. Without blue light (left) the red beam
is not affected, but with blue light turned on
(right) the liquid acts as a defocusing lens. Optical
nonlinearities of the nanoparticle suspension
are the origin of this effect.
2007
U. Heinemeyer, M. C. Wengler, K. Buse “Annihilation of the OHabsorption
due to domain inversion in MgO-doped lithium niobate
crystals” Appl. Phys. Lett. 89, 112910/1-2 (2006)
U. Hartwig, M. Kösters, Th. Woike, K. Buse “High-temperature-recorded
index gratings in periodically-poled lithium niobate” Opt. Lett. 31, 3267-
3269 (2006)
2007
B. Sturman, O. Beyer, D. Maxein, K. Buse “Femtosecond recording and
time-resolved readout of spatial gratings in lithium niobate crystals”
J. Opt. Soc. Am. B 24, 419-429 (2007)

Transmission of a focused
5 W beam of 532 nm wavelength
through undoped
congruent LiNbO thermo-
3
electrically oxidized (left)
and as-grown (right); the
treatment refines the material
and avoids the so-called
“optical damage“.
M. Falk, J. Japs, Th. Woike, K. Buse “Charge transport in highly irondoped
oxidized lithium niobate single crystals” Appl. Phys. B 87, 119-
122 (2007)
I. Breunig, R. Sowade, K. Buse “Limitations of the tunability of dualcrystal
optical parametric oscillators” Opt. Lett. 32, 1450-1452 (2007)
O. Caballero-Calero, M. Kösters, T. Woike, K. Buse, A. García-Cabañes,
M. Carrascosa “Electric field periodical poling of lithium niobate crystals
after soft-proton-exchanged waveguide fabrication” Appl. Phys. B 88,
75-78 (2007)
H. A. Eggert, F. Y. Kuhnert, K. Buse, J. R. Adleman, D. Psaltis “Trapping
of dielectric particles with light-induced space-charge fields” Appl. Phys.
Lett. 90, 241909/1-3 (2007)
Transmission of blue light (wavelength
488 nm) through a hole of 150 nm
diameter in a silver film on top of a
lithium niobate crystal. A hologram
in the crystal confines the light by the
so-called phase conjugation such that
it is transmitted through the hole.
Light wavelength of a highpower
laser diode stabilized
with the help of a Bragg
grating. This Bragg grating
locks the emission wavelength
over a large range
of diode currents and diode
temperatures.
M. Falk, Th. Woike, K. Buse “Reduction of optical damage in lithium
niobate crystals by thermo-electric oxidization” Appl. Phys. Lett. 90,
251912/1-3 (2007)
F. Kalkum, H. A. Eggert, T. Jungk, K. Buse “A stochastical model for
periodic domain structuring in ferroelectric crystals” J. Appl. Phys. 102,
014104/1-5 (2007)
J. R. Schwesyg, H. A. Eggert, K. Buse, E. Sliwinska, S. Khalil, M. Kaiser,
K. Meerholz “Fabrication and optical characterization of stable suspensions
of iron- or copper-doped lithium niobate nanocrystals in heptane”
Appl. Phys. B 89, 15-17 (2007)
M. Falk, Th. Woike, K. Buse “Charge compensation mechanism for
thermo-electric oxidization of lithium niobate crystals” J. Appl. Phys.
102, 063529/1-4 (2007)
37

38
Cage for light. The bright round disk is
a whispering-gallery-mode resonator
made of a lithium niobate crystal.
Once light is coupled into the resonator
by a prism, it is kept inside by total
internal reflections, and very high
intensities can be achieved. These
resonators are a path to miniaturize
devices to make then cheap and
portable.
2008
P. Reckenthaeler, D. Maxein, Th. Woike, K. Buse, B. Sturman “Separation
of optical Kerr and free-carrier nonlinear responses with femtosecond
light pulses in lithium niobate crystals” Phys. Rev. B 76, 195117/1-4
(2007)
I. Breunig, M. Falk, B. Knabe, R. Sowade, K. Buse, P. Rabiei,
D. H. Jundt “Second harmonic generation of 2.6 W green light with
thermoelectrically oxidized undoped congruent lithium niobate crystals
below 100 °C” Appl. Phys. Lett. 91, 221110/1-3 (2007)
2008
I. Breunig, J. Kiessling, B. Knabe, R. Sowade, K. Buse “Hybridly-pumped
continuous-wave optical parametric oscillator” Opt. Express 16, 5662-
5666 (2008)
An intra-cavity amplifier, being pumped incoherently
(pump power P ), is able to lower the
D
threshold of an optical parametric oscillator by
more than one order of magnitude. Thus instead
of expensive high-power pump lasers cheap
laser diodes can be employed.
K. Brands, M. Falk, D. Haertle, Th. Woike, K. Buse “Impedance spectroscopy
of iron-doped lithium niobate crystals” Appl. Phys. B 91, 279-281
(2008)
I. Breunig, J. Kiessling, R. Sowade, B. Knabe, K. Buse “Generation of
tunable continuous-wave terahertz radiation by photomixing the signal
waves of a dual-crystal optical parametric oscillator” New Journal of
Physics 10, 073003 (2008)
J. R. Schwesyg, H. A. Eggert, J. R. Adleman, K. Buse “Spatially resolved
holographic measurements of the thermal diffusivity in liquids” Appl.
Phys. B 92, 79-81 (2008)
D. Maxein, S. Kratz, P. Reckenthaeler, J. Bückers, D. Haertle, T. Woike,
K. Buse “Polarons in magnesium-doped lithium niobate crystals induced
by femtosecond light pulses” Appl. Phys. B 92, 543-547 (2008)

Tunable continuous-wave
terahertz radiation is generated
by photomixing the
signal waves of a dual-crystal
optical parametric oscillator.
S. Gronenborn, B. Sturman, M. Falk, D. Haertle, K. Buse “Ultraslow
shock waves of electron density in LiNbO 3 crystals” Phys. Rev. Lett. 101,
116601/1-4 (2008)
2009
J. Kiessling, R. Sowade, I. Breunig, K. Buse, V. Dierolf “Cascaded optical
parametric oscillations generating tunable terahertz waves in periodically
poled lithium niobate crystals” Optics Express 17, 87-91 (2009)
J. R. Schwesyg, T. Beckmann, A. S. Zimmermann, K. Buse,
D. Haertle “Fabrication and characterization of whispering-gallery-mode
resonators made of polymers“ Optics Express 17, 2573-2578 (2009)
Ultraslow shock-waves of electron density are
obtained through thermo-electrical oxidization
of iron-doped lithium niobate crystals.
F. Luedtke, J. Villarroel, A. García-Cabañes, K. Buse, M. Carrascosa
“Correlation between photorefractive index changes and optical damage
thresholds in z-cut proton-exchanged-LiNbO 3 waveguides” Optics
Express 17, 658-665 (2009)
F. Kalkum, K. Peithmann, K. Buse “Dynamics of holographic recording
with focused beams in iron-doped lithium niobate crystals” Optics
Express, 17, 1321-1329 (2009)
M. Kösters, B. Sturmann, D. Haertle, K. Buse “Kinetics of photorefractive
recording for circular light beams“ Opt. Lett. 34, 1036-1038 (2009)
T. Vitova, J. Hormes, M. Falk, K. Buse “Site-selective investigation of
site-symmetry and site-occupation of iron in Fe-doped lithium niobate
crystals” J. Appl. Phys. 105, 013524/1-6 (2009)
39

2009
40
A whispering-gallery mode coupled out (left)
and a simulation of the corresponding mode in
the resonator (right). The simulation gives the
intensity of the light along a vertical cut of the
resonator, whose surface is shown in white. It
corresponds to the near field of the out-coupled
mode. The values q, l, m are the quantum numbers
of the mode. Studies like this allow further
miniaturization of frequency converters.
H. Steigerwald, F. Luedtke, K. Buse “Ultraviolet-light assisted periodic
poling of near-stoichiometric, magnesium-doped lithium niobate crystals”
Appl. Phys. Lett. 94, 032906/1-3 (2009)
F. Kalkum, S. Broch, T. Brands, K. Buse “Holographic phase conjugation
through a sub-wavelength hole” Appl. Phys. B 95, 637-645 (2009)
J. Japs, M. Falk, Th. Woike, K. Buse, B. Sturman “Relaxation dynamics of
space-charge gratings excited by nanosecond light pulses in highly irondoped
LiNbO 3 crystals” Appl. Phys. B 95, 413-419 (2009)
E. Sliwinska, S. Mansurova, U. Hartwig, K. Buse, K. Meerholz “Effect of
co-sensitization in new hybrid photorefractive materials based on PVK
polymer matrix and inorganic LiNbO 3 nano-crystals” Appl. Phys. B 95,
519-524 (2009)
A light brush cleans nonlinear crystals,
suppresses optical damage, and
hence enables efficient generation of
high-power laser light.
F. Kroeger, I. Breunig, K. Buse “Frequency stabilization and output power
undulations of diode lasers with feedback by volume holographic gratings”
Appl. Phys. B 95, 603-608 (2009)
D. Maxein, J. Bueckers, D. Haertle, K. Buse “Photorefraction in
LiNbO 3 :Fe crystals with femtosecond pulses at 532 nm” Appl. Phys. B
95, 399-405 (2009)
J. Bueckers, D. Maxein, D. Haertle, K. Buse “Light-induced scattering of
femtosecond laser pulses in iron-doped lithium niobate crystals” J. Opt.
Soc. Am. B 26, 1018-1022 (2009)
R. Sowade, I. Breunig, J. Kiessling, K. Buse “Influence of the pump
threshold on the single-frequency output power of singly-resonant optical
parametric oscillators” Appl. Phys. B 96, 25-28 (2009)

Cascaded nonlinear processes are
observed in optical parametrical oscillators
at high pump powers. Here the
primary signal wave acts as the pump
wave for the generation of terahertz
radiation.
M. Kösters, B. Sturmann, P. Werheit, D. Haertle, K. Buse “Optical cleaning
of lithium niobate crystals” Nature Photonics 3, 510-513 (2009)
S. Mansurova, K. Meerholz, E. Sliwinska, U. Hartwig, K. Buse “Enhancement
of the charge carrier transport by doping PVK-based photoconductive
polymers with LiNbO 3 nanocrystals” Phys. Rev. B 79, 174208/1-7
(2009)
P. Ganguly, C. L. Sones, Y. J. Ying, H. Steigerwald, K. Buse, E. Soergel,
R. W. Eason, S. Mailis “Determination of refractive indices from the
mode profiles of UV-written channel waveguides in LiNbO 3 crystals for
optimization of writing conditions” Journal of Lightwave Technology 27,
3490-3497 (2009)
2010
Cascaded nonlinear processes in optical
parametric oscillators based on periodicallypoled
lithium niobate allow generation of
narrow-band, tunable, and diffraction-limited
continuous-wave terahertz radiation with more
than 2 µW power.
M. Kösters, C. Becher, D. Haertle, B. Sturman, K. Buse “Charge transport
properties of undoped congruent lithium niobate crystals” Appl. Phys. B
97, 811-815 (2009)
R. Sowade, I. Breunig, I. C. Mayorga, J. Kiessling, C. Tulea, V. Dierolf,
K. Buse “Continuous-wave optical parametric terahertz source” Optics
Express 17, 22303-22310 (2009)
41

42
Team

44
The team during an internal workshop at Maria in der Aue.
Team
Current team
We are very happy about the strong interest raised by
our activities. This is reflected in the high number of
applications of students who want to conduct scientific
work in the “Hertz team”.
PhD students
• Tobias Beckmann
• Jens Kießling
• Bastian Knabe
• Fabian Lüdtke
• Michael Kösters
• Dominik Maxein
• Judith Schwesyg
• Daniel Schütze
• Rosita Sowade
• Hendrik Steigerwald
• Niklas Waasem
Diploma students
• Felix von Cube
• Heiko Linnenbank
Theses accomplished at the Heinrich
Hertz Chair of Deutsche Telekom AG
Each student receives a special training that goes
beyond physics. We are putting also attention on organization,
documentation, and presentation of projects.
Active participation in international conferences and
research occupations for some months abroad at internationally
leading institutions are a must at least for
our PhD students.
PhD theses
• Dr. Felix Kalkum (2009 - Dt. Telekom AG)
• Dr. Ingo Breunig (2009 - University of Bonn)
• Dr. Matthias Falk (2008 - Crystal Technology, USA)
• Dr. Witold Kandulski (2007 - Stevenage Circuits, UK)
• Dr. Helge Eggert (2006 - light power instruments, Berlin)
• Dr. Ulrich Hartwig (2006 - Osram, Berlin)
• Dr. Dirk Apitz (2005)
• Dr. Oliver Beyer (2005 - Carl Zeiss SMT, Oberkochen)
• Dr. Mark Wengler (2005 - Carl Zeiss SMT, Oberkochen)
• Dr. Nils Benter (2005 - Philips, Aachen)
• Dr. Birk Andreas (2005 - PTB Braunschweig)
• Dr. Ralph Bertram (2004 - Osram, Regensburg)
• Dr. Manfred Müller (2004 - Philips, Eindhoven)
• Dr. Dirk Berben (2003 - Osram, München)
• Dr. Marc Lünnemann (2003 - Osram, Herbrechtingen)
Diploma theses
• Carsten Becher (2009)
• Frank Lars Behm (2009)
• Sergej Hermann (2009)

• Cristian Tulea (2009)
• Johanna Bückers (2008)
• Anne Zimmermann (2008)
• Stephan Gronenborn (2008)
• Dennis Beckmann (2007)
• Sebastian Broch (2007)
• Patrick Werheit (2007)
• Stephan Kratz (2007)
• Katharina Brands (2006)
• Thorsten Hoffmann (2006)
• Roland Krüppel (2006)
• Peter Reckenthäler (2006)
• Felix Kuhnert (2006)
• Felix Kröger (2006)
• Ute Heinemeyer (2005)
• Julius Japs (2005)
• Benedikt Hecking (2004)
• Boris Faßbender (2004)
• Clemens von Korff Schmising (2003)
• Holger Blank (2003)
• Johannes Spanier (2002)
Master theses
• Mathieu Gentile (2007)
Bachelor theses
• Manuel Peter (2009)
• Matthias Schönborn (2009)
Alumni hiking along the Rhine river.
Alumni network
Many of our alumni keep in close contact on a personal
basis. Once a year we also organize a meeting
in Bonn where all alumni are invited to exchange
information, to keep up to date on current research
projects, and just to enjoy meeting old friends again.
This network is very relevant, especially to younger
students who need access to trainee programs, job
openings and practical advice from those who have
built a career in industry.
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46
Careers

Careers
To give readers an idea of how the careers of our
alumni have evolved, we asked five of our former students
to tell us about what they have been doing. They
were all keen to provide the information, so we have
compiled the following brief CVs.
Dr. Ingo Gerhard Nee
Dr. Ingo Gerhard Nee
Dr. Ingo Gerhard Nee (*1973) studied physics at the
University of Osnabrück, where he also obtained his
PhD working under Prof. Dr. K. Buse. Together with
a team of researchers from the Universities of Bonn
and Osnabrück as well as the California Institute of
Technology (Caltech), he co-founded the start-up company
Ondax, Inc. in Los Angeles in 2001. He became
the director of R&D responsible for the development
of optical filters for telecommunication technology. In
2003, following a post-doc posting at the University of
Bonn, again in Prof. Buse‘s group, he moved to Auto-
Vision GmbH, a company belonging to Volkswagen AG.
There, he led various projects as a consultant in the
incubator section for internal consulting. Since 2004,
Dr. Nee has been employed at the Rosen Research and
Technology Center (RTRC) in Lingen. The RTRC is part
of the Rosen group and a market leader in services
for nondestructive inspection of pipelines and fuel
depots. Rosen operates globally and employs over
1700 people worldwide. Dr. Nee began as a physicist
and became head of R&D for novel and innovative
technologies and products in 2005. Within this function
he heads an international team of more than 140
researchers, engineers, and technicians, covering the
fields of machine construction, electrical engineering,
computing, physics and chemistry.
Dr. Marc Lünnemann
Dr. Marc Lünnemann
Dr. Marc Lünnemann (*1974) studied physics at
the University of Osnabrück and then moved to the
University of Bonn in order to work on his PhD in the
Hertz team. His studies focused on the effects occurring
in nonlinear crystals for very large externally
applied electrical fields.
After finishing his PhD, he decided to join the OSRAM
Automotive Application Center near Ulm in April
2004. Three years of developing new light sources
and lighting applications for the automotive industry
gave him significant insights into the industry. In
mid-2007, Dr. Lünnemann decided to join OSRAM
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48
Corporate Strategy in Munich, giving him a broader
perspective on the company and the lighting industry
as a whole. In parallel, OSRAM sent him to take part
in the Executive MBA Corporate Management program
at the University of Augsburg, which is run in collaboration
with the Katz Graduate School of Business at
the University of Pittsburgh (USA). He successfully
completed this program in October 2008. In January
2009 the former Automotive Lighting and Display/
Optics business units were consolidated into a single
business unit called Specialty Lighting (SP). In his
corporate strategy function Dr. Lünnemann assisted
the business heads in completing the merger and was
asked in April 2010 to join the new SP business unit
in the newly created position of Manager of Business
Development & Strategy.
In this function Dr. Marc Lünnemann is responsible for
the development and execution of SP’s long term
strategy. Given the dynamic nature of today’s lighting
market, an ongoing effort is needed to make sure that
SP has the right products, technologies, core competencies,
business partners and organizational structure
to assure future success. Strategy development
involves analyzing market trends, analyzing competitive
developments, defining the business unit‘s value
proposition, and identifying new business opportunities,
potential new market segments and potential
new business models. Additionally, Dr. Lünnemann
consults top management on strategic matters and is
tasked with steering and driving specific projects (i.e.
merger and acquisition projects) across all the global
functions required to support the overall strategy.
Dr. Mark Wengler
Dr. Mark Wengler
Dr. Mark Wengler (*1976) performed his studies in
physics at the Universities of Dortmund, Sydney and
Bonn. In his diploma project at the Heinrich Hertz
Foundation Chair of the Deutsche Telekom he investigated
the domain inversion of lithium niobate crystals,
developing and implementing novel experimental
methods for this purpose in Karsten Buse’s brand new
laboratories. Mark Wengler continued his research as
a scholarship holder of the Deutsche Telekom Stiftung
during his PhD project. He graduated in 2005. His
investigations of light-supported domain inversion
improved the understanding of these effects and
enabled simplified production processes for special
optical components (i.e. periodically-poled lithium
niobate, PPLN) to be widely used for frequency conversion
applications.
In 2005 Mark Wengler started his career in industry
as a research scientist at the Philips Research Laboratories,
investigating pharmacokinetic models and
developing molecular imaging solutions for medical
applications. Since 2006 he works for the Carl Zeiss
SMT AG in various development projects for optical
lithography systems. After working as a development
engineer and part-project leader for conventional il-

lumination systems, he headed a project in 2009 as
part of a major development program for next-generation
extreme ultra-violet lithography systems.
Dr. Felix Kalkum
Dr. Felix Kalkum
Dr. Felix Kalkum (*1980) graduated from the University
of Bonn in 2005, receiving diplomas in physics
and mathematics. He received his PhD in physics in
the Hertz group in 2009. During his time at the University
of Bonn he was active as a student representative,
being president of the student‘s parliament and
member of the University Senate. He was awarded a
scholarship by the Deutsche Telekom Stiftung during
his PhD studies.
In 2010 he joined the Detecon, an affiliate of the
Deutsche Telekom specializing in integrated management
and technology consulting.
Manuel Peter
Manuel Peter
Manuel Peter (*1988) is the first student to complete
his Bachelor thesis in the new Bachelor/Master
study program of the Department of Physics and
Astronomy at the University of Bonn. In his threemonth
internship in spring 2009 with the Hertz team,
he contributed successfully to the realization of an
“optical hammer“, which pushes light through holes
of subwavelength dimension (smaller than 1/1000 of
a millimeter). We are glad that outstanding students
like him are attracted by the work performed in the
Hertz research group: Manuel Peter had already
shown at high school his outstanding capabilities and
started to attend classes at the University even before
completing his school leaving exam. He completed his
Bachelor studies ahead of time, and received a degree
at the age of 21. He was also recently awarded a
grant by the “Studienstiftung des Deutschen Volkes“.
In addition to his professional activities, he is socially
and politically committed, including being a member
of the board of the Lohmar City Council in charge for
environmental issues and young people‘s issues.
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Cooperation

Cooperation
The Heinrich Hertz Chair is very well connected,
within Bonn, across Germany, and internationally.
In Bonn, we took the responsibility of coordinating
research activities in the fields of photonics and
condensed-matter physics.
The main achievement has been gaining DFG approval
of our research unit on “Light confinement and control
with structured dielectrics and metals“. This unit
has total funding of about € 3 million has brought
together about 40 scientists from eight different
research teams since 2004. Prof. Dr. Karsten Buse is
the spokesperson for the research unit.
Workshop of the DFG research unit in the Physics
Centre of the DPG at Bad Honnef.
Participating Principal Investigators
• Dr. Wolfgang Alt: Quantum Optics,
University of Bonn
• Prof. Dr. Karsten Buse: Applied Optics,
University of Bonn
• Dr. Dmitry N. Chigrin: Condensed Matter Theory,
University of Wuppertal
• Prof. Dr. Manfred Fiebig: Nonlinear Magnetooptics,
University of Bonn
• Prof. Dr. Harald Giessen: Ultrafast Nano-Optics,
University of Stuttgart
• Dr. Daniel Haertle: Nonlinear Optics,
University of Bonn
• Prof. Dr. Hans Kroha: Condensed Matter Theory,
University of Bonn
• Prof. Dr. Karl Maier: Condensed Matter Physics,
University of Bonn
• Prof. Dr. Dieter Meschede: Quantum Optics,
University of Bonn
• Dr. Konrad Peithmann: Nonlinear Materials,
University of Bonn
• Prof. Dr. Arno Rauschenbeutel: Quantum Optics,
University of Mainz
• Prof. Dr. Moritz Sokolowski: Organic Films,
University of Bonn
• Prof. Dr. Martin Weitz: Ultracold Gases,
University of Bonn
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52
Dielectrics and metals are structured in order to
enhance the light-matter interaction. Enhanced
interaction strengths promise increased sensitivity, efficiency,
compactness, and speed of photonic devices.
Waveguides as well as resonators are used. Clusters
of projects employ the following principles in order to
enhance the light-matter interaction:
Trapping of light
Whispering-gallery-mode and Bragg resonators with
very high quality factors and finesse are directly made
of nonlinear-optical crystals. Nonlinear optics with
outstanding efficiencies is envisaged.
Evanescent waves
In ultrathin fibers light waves will be transformed
almost completely into evanescent waves. Very strong
interaction of the surface layer with the propagating
light field promises interesting applications in sensing
and nonlinear optics.
Electronic resonances
Resonances of electronic transitions in atoms,
molecules, or nanoscopic resonators will be used to
enhance, e.g., the second- or third-order nonlinearities.
Atoms will be combined especially with fiber
resonators, invented within the research unit.
Three dimensional metamaterial made out of stacked gold nanoantennas
in order to realize a new optical sensor (Na Liu, Lutz
Langguth, Thomas Weiss, Jürgen Kästel, Michael Fleischhauer,
Tilman Pfau, Harald Giessen, Nature Materials 8, 758 - 762
(2009)).
Plasmonic resonances
Excitation of plasmons can cause field enhancements.
The underlying physics will be explored and the field
enhancement will be maximized. In combination with
nonlinear dielectrics, composite materials promise
superior nonlinear-optical functionalities.
It is extremely fascinating to explore how far the limits
of strong light-matter interaction can be pushed.
One may envision nonlinear optics at the level of few
photons, the convenient optical detection of single
atoms and molecules, and the deterministic coupling
of single photons to single atoms.

Deutsche Telekom Laboratories
Deutsche Telekom Laboratories were founded in
2005 as the research and development establishment
of Deutsche Telekom, but also as an associated
scientific institute of the Technical University of
Berlin resourced with seven professorships. The link
between Deutsche Telekom’s R&D activities and the
TU Berlin along with other universities, institutes and
industry partners has led to ever closer ties between
the worlds of science and business. For Telekom, the
major benefit of this partnership is that new solutions
are being identified, matured and brought onto
market in a very short time.
Deutsche Telekom Laboratories are mainly situated
directly on the TU Berlin campus. There are more
than 350 Deutsche Telekom experts and scientists
in various disciplines from all over the world working
here and at other sites in Berlin and Darmstadt to
engineer solutions and innovations for the simple, fast
and secure communications of tomorrow. Telekom
Laboratories collaborate closely with the Ben-Gurion
University in Israel and Deutsche Telekom’s R&D lab
in Los Altos (Silicon Valley), United States.
Research and development at Deutsche Telekom
Laboratories is user-driven. It is based on an open
innovation model and the conviction that collective
know-how can only be developed within a network of
partners. Organizationally, the labs are divided up
into the Innovation Development Laboratory and the
Strategic Research Laboratory.
The centre of the Deutsche Telekom Laboratories is located in
Berlin at the Ernst Reuter Platz on the campus of the Technical
University of Berlin.
The Innovation Development Laboratory develops new
services and solutions for Deutsche Telekom customers
over a project period of one-and-a-half to three
years. The experts work with both external and internal
partners and transfer the results to the marketoriented
Group units for commercial application.
The Strategic Research Laboratory focuses on longterm
technology research and applied research. The
groundwork for tomorrow’s communications technologies
is being laid in its scientific research projects.
Teaching is provided at the TU Berlin by the seven
professorships. The researchers are also actively
involved in international standardization bodies. As an
integral part of a global scientific network, TU Berlin
acts as a hub for new ideas.
Telekom Laboratories are headed by Peter Möckel
and his team: Dr. Heinrich Arnold, Dr. Udo Bub, Dr.
Raimund Schmolze and Klaus J. Buß.
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National and international close
cooperation partners:
• Autonomous University of Madrid
• California Institute
of Technology (Caltech)
• EPFL Lausanne
• Lehigh University
• Massachusetts Institute
of Technology (MIT)
• PennState University
• Stanford University
• University of Cologne
• University of Paderborn
• University of Southampton
• Bayer AG
• Crystal Technology, Inc.
• Ondax, Inc.
• Schott AG
• Deutsche Telekom AG
• caesar
• Deutsche Forschungsgemeinschaft (DFG)
• Deutsche Telekom Stiftung
• VolkswagenStiftung

Guest Scientists
Over the years we had many visitors from several
institutions around the world, working with us just
for some weeks or for up to half a year. Just three
occupations are highlighted in the following. All sides
benefited strongly from this personal exchange.
Prof. Dr. Volkmar Dierolf
Volkmar Dierolf
Volkmar Dierolf was with us for half a year as a DFG
Mercator Guest professor. He is Professor of Physics
and Chair of the Department of Physics at the Lehigh
University, USA and also holds a joint appointment
with the Materials Science and Engineering Department.
He obtained his PhD in physics at the University
of Utah, Salt Lake City, Utah (USA) and returned
to Germany to work at the University of Paderborn,
as a research scientist and group leader in the field
of “Optical Spectroscopy of LiNbO 3 waveguides”. He
also obtained his “habilitation” in experimental physics
at the same place before leaving again to the USA,
this time as an Associate Professor, Lehigh University,
Bethlehem.
Volkmar Dierolf professional expertise can – among
others – be deduced from the large number of highly
recognized publications, his appointment of a Mercator
Visiting Professor at the University of Bonn and
the Lehigh University Joseph F. Libsch Early Career
Research Award, which honors faculty members
who are early in their research career and who have
demonstrated the potential for high-quality research
and scholarship. Since 2006, Volkmar Dierolf and
Karsten Buse lead a NSF/DFG funded Materials World
Network collaboration on in which five groups from
the USA and Germany work on questions related to
the Nanoscale Structure and Shaping of Ferroelectric
Domain Walls.
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56
Prof. Dr. Boris I. Sturman
Prof. Dr. Boris I. Sturman
Boris I. Sturman works in Bonn for about four months
each year. He is affiliated with the Institute of Automation
and Electrometry in Novosibirsk, Russia and
has recently been elected for the highest possible research
position in the Russian Academy of Sciences,
he became a “General Research Fellow”. This position
is reserved for only a few percent of the research
staff and requires outstanding scientific results and
achievements. Professor Sturman studied in Russia
at highly respected institutions and joined in 1976
the Institute of Automation of Electrometry (IAE) in
Novosibirsk, first as a Junior Researcher, followed by
a Senior Research Fellow and finally, after having been
Assistant Professor at the Novosibirsk State University
for a decade, he became the head of the laboratory of
nonlinear optics at the IAE being a Leading Research
Fellow at the IAE.
In parallel to his impressive carrier at the IAE he took
the opportunity to work for longer periods of time as
a guest researcher in Denmark, Germany, Finland,
France and Spain, where he was highly welcome owing
to his outstanding expertise in nonlinear optics and
transport phenomena in solid state materials. Since
2001 he is a regular guest in the group of Prof. Dr. K.
Buse. More than a dozen of common publications in
reputed journals attest for this very fruitful cooperation
which is to be continued.
Prof. Dr. Demetri Psaltis
Prof. Dr. Demetri Psaltis
Demetri Psaltis has collaborated with Karsten Buse
since 1996. He was awarded a Humboldt Research
Prize, allowing him to spend longer periods of time in
Bonn. At present he is Professor and Director of the
Optics Laboratory at the École polytechnique fédérale
de Lausanne (EPFL) as well as Dean of the School
of Engineering at the EPFL. He obtained his PhD in
Electrical Engineering at the Carnegie-Mellon University
in 1977. He then became Assistant Professor of
Electrical Engineering at the California Institute of
Technology (Caltech), where he pursued his career
up to the position of Thomas G. Myers Professor of
Electrical Engineering.
Thanks to his broad range of research interests – from
nonlinear optics and holography combined with optical
information data processing to opto-fluidics and
bio-photonics – he has received a number of honors,
such as his appointment as Fellow of the Optical Society
of America or award of the Humboldt Research
Prize for Senior U.S. Scientists. He is considered to
be one of the most influential scientists in applied
optics. Besides his academic career, he is also a successful
entrepreneur, as indicated by over 45 patents
and, moreover, by his successful start-ups, including
Ondax Inc.

Entrepreneurship
It is our goal to turn the scientific results we achieve
into applications that can drive our economy and
provide benefits for our society. To this end we license
research outcomes by registering patents and, in one
case so far, founding start-up companies.
In 2000, we developed optical filters that can split
optical waves – based on their color – with very high
selectivity. The filters employ “volume holograms“.
Photorefractive lithium niobate crystals were used
first. Later we developed, together with a large German
glass-maker, a photosensitive glass that is now
being used in the manufacture of such filters. The
filters have a unique property: Waves with a relative
difference of light wavelengths of less than 1/1000
can be separated. This is of relevance to, for instance,
fiber-optical networks.
Having grasped the commercial potential of our
development, we joined with colleagues from the
California Institute of Technology to found Ondax Inc.,
a company located in Monrovia, California. Ondax Inc.
received about € 10 million in venture funds and after
just 18 months released its first product.
The headquarter of the Ondax company.
With the downturn of economy in 2001 we added new
products to broaden our portfolio, using the same
optical filtering technique. Laser diodes were stabilized
by providing a wavelength-selective feedback.
Telescope filters were developed to suppress special
light wavelengths originating from, for instance, excitations
of water in the atmosphere. The company also
produces filters for Raman spectroscopy.
Most recently we released chirped filters for compression
and expansion of ultrashort light pulses. – The
Ondax filters are used these days in many devices and
labs around the world, including the quantum optics
labs run by our colleagues in Bonn.
57

Outreach

Teaching

Outreach
Teaching
According to the Humboldt principle, research and
teaching are mutually complementary and should be
conducted together. Indeed, the interaction between
professors engaged in research and students, who are
the up-coming generation of scientists, is extremely
fruitful, raising many good questions and producing
new ideas. This is essential for the work of universities.
The Heinrich Hertz Chair has contributed significantly
to the teaching effort. We run seminars, lab
courses and colloquia, as well as many other classes.
To illustrate the kind of classes we offer, here is a
brief selection:
• Laser physics and quantum optics
• Holography
• Optical measurement techniques
• Optical image processing
• Integrated optics
• Optical material processing
• Applied optics
• Atomic physics
• Photonics
• Solid state physics
• Advanced photonics and quantum optics
Education of future scientists: Prof. K. Buse giving a lecture at
the Wolfgang Paul lecture hall in Bonn.
University of Bonn – self-administration
Today, German universities fortunately enjoy a pretty
large degree of autonomy. This independence demands,
however, that all professors spend time on the
processes of self-administration to ensure effective
management and a forward-looking strategy. We have
contributed in various ways to this self-government.
The Heinrich Hertz Chair was deeply involved in setting
up a tenure-track system for appointing of professors.
Prof. Dr. Karsten Buse also spend two one-year
terms as the elected director of the Institute of Physics,
overseeing about 200 employees.
61

62
Events
It is fun showing our work to the public, to experts or
to students. We have had some excellent opportunities
to do so. Not only have plenty of talks been given
over the years, but also more than 100 guided tours
arranged through our research labs. Here is a small
selection of special events in recent years:
At the 2003 “Internationale Funkausstellung“ in Berlin
we presented some of our photonic developments
in the booth of Deutsche Telekom and drew strong
attention.
For the open day at the headquarters of the Deutsche
Telekom on August 17, 2007, we put on a presentation
and laser shows for the public.
Laser beam leaving the physics building in the Wegelerstr. 8
and shining across the city of Bonn.
The key-note speech was given for the “Science Days“
held at the University of Applied Sciences/University
of Telecommunications in Leipzig.
On the occasion of the 150th birthday of our namesake,
Heinrich Hertz, we invited the public to meet us
and tour the labs on a Sunday afternoon, December
9, 2007. More than 400 people came and were excited.
This was another opportunity to illuminate the
sky over Bonn with laser beams.
From June 11, 2009 to June 15, 2009 the international
conference on “Photorefractive Materials, Effects, and
Devices: Control of Light and Matter“ was held at the
Deutsche Telekom Tagungshotel in Bad Honnef. More
than 180 participants from all around the globe attended
this very lively meeting.