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Q 40 Laserspektroskopie
Zeit: Donnerstag 16:30–18:30 Raum: HS 204
Q 40.1 Do 16:30 HS 204
New Trends in Apertureless Scanning Near-field Optical Microscopy
— •Javad Farahani, Hans -Juergen Eisler, and Bert
Hecht — Nano-Optics Group, Dept. of Physics, University of Basel,
Klingelbergstr. 82 CH-4056 Basel, Switzerland
Over the last years to overcome the problems of aperture SNOM, different
techniques for apertureless SNOM have been exploited. In this
work, we demonstrate that using small metal structures on a dielectric
tip, illuminated by laser can be, potentially used to increase spatial resolution
of optical microscopy far beyond the diffraction limit. The set-up
is based on a combination of contact-mode AFM and confocal microscope.
Depending on the direction of polarization of the incoming beam,
fluorescence can be either enhanced or quenched, which in both case the
fluorophore is recognized with resolution higher than diffraction limit.
Q 40.2 Do 16:45 HS 204
Towards single-molecule detection by absorption —
•Jacqueline Y.P. Butter and Bert Hecht — Nano-Optics
group, Institute for Physics, University of Basel, Klingelbergstr. 82,
CH-4056 Basel, Switzerland
At cryogenic temperatures many temperature activated processes are
frozen out, resulting in extremely sharp zero-phonon lines in fluorescence
excitation spectra of certain molecule-matrix systems. The presence of
sharp absorption lines is accompanied by the fact that the absorption
cross section of a single molecule approaches the theoretical limit for
an oscillating dipole. However, the spatial resolution in confocal microscopy
is limited by the diffraction limit. Near-field excitation can be
used to overcome this limit. Using near-field excitation, the light source
can eventually be made smaller than the absorption cross section of a
single molecule. The aim of our experiment is to look at the interaction
of strongly confined light fields with single molecules. The set up we use,
is a combination of a scanning confocal optical microscope and a scanning
probe microscope, which is suitable for operation at both room and
cryogenic temperature. A single-mode ring dye laser is used to excite the
molecules and to perform spectroscopy at cryogenic temperature.
Q 40.3 Do 17:00 HS 204
Interaction of a single molecule with sharp metal tips at low
temperature — •Senta Karotke and Bert Hecht — Nano-Optics
group, Institute of Physics, University of Basel, Klingelbergstrasse 82,
CH-4056 Basel
A very interesting topic, which becomes accessible experimentally, is
the examination of the properties of single quantum systems like single
molecules and their interactions.
Single molecules at cryogenic temperature are very sensitive probes
for optical and electrical processes in their local environment. For example,
the resonance of a molecule in the vicinity of a sharp metal tip is
shifted. This shift occures either due to the interaction of the molecule
with its backreflected field or, if a voltage is applied to the tip, due to the
Stark effect. This fact can be exploited for high-resolution localization
and imaging of single molecules or other quantum systems.
The experimental investigations are carried out by using the wellestablished
technique of a confocal microscope which is combined with
a newly developed scanning tip setup with a tuning fork shearforce gapwidth
control. In the temperature range from RT down to cryogenic T,
we are able to record topographic images as well as optical images. We
will present results showing tip-induced Stark effect of a single molecules,
i.e. the frequency shift of single molecules as a function of the tip position.
This demonstrates a new powerful technique of resolving single molecules
with a spatial resolution only limited by the characteristic size of the tip.
Q 40.4 Do 17:15 HS 204
Präzisionsspektroskopie mit verschränkten Zuständen —
•Christian Roos, Michael Chwalla, Mark Riebe, Jan
Benhelm, Christoph Becher, Wolfgang Hänsel, Hartmut
Häffner, Ferdinand Schmidt-Kaler und Rainer Blatt —
Institut für Experimentalphysik
Präzisionsspektroskopie an atomaren Bellzuständen bietet nicht nur
den Vorteil eines verbesserten Signal-Rausch-Verhältnisses sondern
darüber hinaus die Gelegenheit, die spektroskopischen Eigenschaften die-
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ser ”Superatome” für die Messung masszuschneidern. Wir zeigen, dass
in Experimenten mit zwei verschränkten 40 Ca + Ionen der Zeeman-Effekt
1. Ordnung eliminiert werden kann, obwohl keinerlei m = 0 → m = 0
Übergänge existieren. Darüberhinaus lassen sich Frequenzverschiebungen
optischer Übergänge, die durch externe Felder verursacht werden und im
Bereich weniger Hertz liegen, mithilfe von Bellzuständen detektieren und
vermessen. Für Atomuhren auf Ionenfallenbasis ist dabei die elektrischen
Quadrupolverschiebung von grosser Bedeutung sowie der Zeeman-Effekt
zweiter Ordnung.
Q 40.5 Do 17:30 HS 204
Simultaneous electromagnetically induced transparency and
absorption in a closed transition — •Luca Spani Molella,
Rolf-Hermann Rinkleff, and Karsten Danzmann — Max-
Planck-Institut für Gravitationsphysik und Institut für Atom- und
Molekülphysik, Universität Hannover, Callinstraße 38, D-30167
Hannover.
Aim of this work is to provide insight into some new phenomena which
occur in a typical EIA (electromagnetically induced absorption) transition.
The F=4 to F’=5 transition of the Cs D2 line is analyzed with a
probe and a coupling laser. A third laser allows simultaneous measurement
of the dispersion of either the probe or the coupling laser (heterodyne
interferometer). At resonance the probe laser shows EIA, while the
coupling shows simultaneously electromagnetically induced transparency.
These results are observed for the first time and are obtained in a range
of several decades for the power of both the probe and the coupling laser.
Since our apparatus is highly sensitive for dispersion measurements, we
are able to present the first results of the coupling laser (parametric)
dispersion as a function of the detuning of the probe laser in the same
closed degenerate two level transition. The coupling laser shows positive
parametric dispersion, which grows to a maximum and then decreases
as a function of laser powers. The dispersion of the probe laser around
the EIA peak is on the contrary negative but shows a similar behaviour
as a function of the laser powers. A brighter negative dispersion signal
superimposed on the previous one is observed at low laser powers.
Q 40.6 Do 17:45 HS 204
Coherent Population Trapping with Variable Doppler Sensitivity
— •Christian Bolkart 1,2 , Danijela Rostahar 1,2 und Martin
Weitz 1,2 — 1 Physikalisches Institut — 2 Auf der Morgenstelle 14; 72076
Tuebingen
Coherent population trapping is a resonance phenomenon which is of
large current interest in the context of slow light, quantum computing
and magnetometry. In a three-level system with two stable ground states
and one spontaneously decaying upper state driven by two laser fields,
atoms can be pumped into a ”dark” coherent superposition of the ground
states. This dark state does not interact anymore with the laser field.
We have studied dark resonances in a thermal gas of rubidium atoms
using a variable angle between the two driving optical beams. The angle
was tuned between a Doppler-free situation (zero angle) and angle near
10 ( − 3) radians, the latter corresponding to the Doppler-sensitivity of a
far infrared photon. We find that the amplitude of the dark resonance
is close to the Doppler-free case as long as the Doppler-effect does not
contribute significantly to the linewidth, but decreases rapidly for larger
angles. We have furthermore recorded similar spectra using rubidium
cells with neon buffer gas, which allows us to investigate the Dicke-effect
in a new regime.
Q 40.7 Do 18:00 HS 204
Slow light by means of spectral hole burning in atomic vapor —
•Jürgen Appel and Alexander I. Lvovsky — Fachbereich Physik
M559, Universität Konstanz
In a Doppler-free spectroscopy setup a rubidium vapor cell is subjected
to two counterpropagating laser beams. The saturating beam creates narrow
spectral holes (of approximately the natural linewidth) in the weaker
signal beam’s Doppler-broadened absorption spectrum. A strong dispersion
leads to a large reduction of the signal pulse’s group velocity at the
transmission peaks and negative group velocities at their edges. Group
indices of order 10 3 with less than 70% absorption have been obtained.