Plenarvorträge - DPG-Tagungen

Halbleiterphysik Montag
sed. Phenomena such as coherent suppression of tunnelling in absence
of accidental degeneration of the quasienergies, low-frequency generation
and half harmonic generation are observed. A simplified analytical model
that reproduces the main features of the numerical calculations is presented
and is utilized to derive simple relations for the values of the pulse
parameters that optimize the control process of the electron motion and
its emission spectrum.
HL 12.21 Mo 16:30 Poster A
Photomixing at 1.55µm - Application of the nipnip-THz-emitter
concept to long wavelength materials — •Frank H. Renner 1 , O.
Klar 1 , S. Malzer 1 , M. Eckardt 1 , G. Loata 2 , T. Löffler 2 , H.
Roskos 2 , D. Driscoll 3 , M. Hanson 3 , A.C. Gossard 3 , and G.H.
Döhler 1 — 1 Insitut für Technische Physik I, Universität Erlangen-
Nürnberg , Germany — 2 Lehrstuhl für Ultrakurzzeitphysik, Universität
Frankfurt a.M., Germany — 3 Materials Departement, UC Santa Barbara,
U.S.A.
We have recently developed a novel concept for photomixing based
on the quasi-ballisitic transport of electrons in a nipnip-superlattice. We
were already able to observe THz-radiation from AlGaAs-based samples.
For these samples excitation is performed by photomixing around 830nm
(see oral presentation of our group).
Technologically more favourable would be a photomixer operating
around 1.55µm. Several workgroups are currently trying to find a suitable
photomixer, operating around this wavelength. In this contribution
we extend our nipnip-THz-emitter concept towards 1.55µm by using the
(Al)InGaAs-semiconductor alloy system. Monte Carlo simulations prove
this material system to be substantially superior to AlGaAs. We will discuss
design and concept of the InGaAs-nipnip-emitter, compare it to the
AlGaAs design and report on first results on its realzation.
HL 12.22 Mo 16:30 Poster A
Molecular fluorescence in and near nanostructures — Lavinia
Rogobete 1 , Vahid Sandoghdar 1 , and •Carsten Henkel 2 —
1 Physical Chemistry, ETH Zurich, Switzerland — 2 Institut für Physik,
Universität Potsdam
Single molecular dipoles provide unique opportunities to perform scanning
optical near field microscopy with pointlike sources and detectors.
The electromagnetic interaction with nanostructured probes and with
the scanning tip itself significantly modifies the fluorescence dynamics.
We discuss a simplified, two-dimensional model for the radiative decay
of a single dipole in a complex dielectric or metallic environment [1]. The
electromagnetic fields are computed numerically using boundary integral
equations. The resulting decay rates inside sub-wavelength host particles
compare well with an electrostatic calculation.
[1] Opt. Lett. 28 (2003) 1736.
HL 12.23 Mo 16:30 Poster A
Optical superlattices based on surface acoustic waves — •M. M.
de Lima, Jr., R. Hey, and P. V. Santos — Paul-Drude-Institut,
Berlin
We present a novel concept for the fabrication of dynamic optical superlattices
based on the modulation of a planar photonic microresonator
by surface acoustic waves (SAWs). The microresonator consists of a λ/4
GaAs cavity layer sandwiched between GaAs/AlAs Bragg reflectors. The
optical superlattice is formed by SAW beams, which laterally modulate
the cavity optical properties. The strong light field in the cavity layer
considerably enhances the acousto-optic interaction, thus leading to high
diffraction intensities. We report the observation of stop bands in the light
dispersion as wide as 1.4 meV induced by the lateral periodicity imposed
by the SAWs. We also demonstrate the formation of two-dimensional
superlattices by the interference of orthogonal SAW beams.
HL 12.24 Mo 16:30 Poster A
Emission stimulation in opals — •Sergei Romanov 1 , Dmitry
Chigrin 1 , Clivia Sotomayor Torres 1 , Nikolai Gaponik 2 , Alexander
Eychmueller 2 und Andrei Rogach 3 — 1 Inst. of Materials
Science and Dept. of Electrical and Information Engineering, University
of Wuppertal, 42097, Germany — 2 Inst. of Physical Chemistry, University
of Hamburg, 20146, Germany — 3 Dept. of Physics, University of
Munich, 80799, Germany
Light sources in photonic crystals (PhCs) attract considerable attention
owing to improvement of emitter parameters. We studied the ballistic
emission of CdTe nanocrystals, which were layer-by-layer embedded in
thin opal films, near the Bragg PBG as a function of excitation power
and angle of detection. Two-parameter exponential fit to the emission
intensity vs. excitation power curve was used to extract the power radiated
by saturated emitter and the saturation threshold. In the PBG the
spectrum of the former shows a minimum in contrast to the maximum of
the latter. The decrease of the saturated emission power was associated
with the suppression of the spontaneous emission rate in a given optical
mode and the increase the saturation threshold - as the acceleration of
the radiative recombination.
We argue that photons emitted along the bandgap direction are coupled
to highly inhomogeneous PhC eigenmodes propagating with low
group velocity. This imposes resonator conditions and the backreaction
of the radiation to emitters stimulates the radiative recombination.
HL 12.25 Mo 16:30 Poster A
Light scattering in thin opal films — •Sergei Romanov — Institute
of Materials Science and Department of Electrical and Information
Engineering, University of Wuppertal, 42097 Wuppertal, Germany
Reflectance and transmission are conventionally used to measure light
interaction with photonic crystals (PhCs), whereas the light scattered
off the incidence direction is neglected. In this work the scattering was
used as an independent tool to study the light propagation in slightly
disordered three-dimensional PhCs. In such crystals the regime of weak
scattering is realised, when scattered photons experience only one collision
along their paths, i.e. they mimic light emitted by an internal light
source.
The intensity of light scattered by thin opal films in forward and backward
configurations was studied as a function of wavelength and direction.
It was shown that diffraction-related minima of forward scattered
light do not depend on the actual lightpath, but correspond to directions
of the incidence and detection with respect to (111) planes. Angle diagrams
of the scattered light were assigned to the resonant scattering,
moreover, they show a modulation by shadows of respective bandgaps.
Oppositely, the backscattering appears more effective at bandedges of
the Bragg gap.
As an example, the light scattering was used to characterise the light
propagation across the PhC heterojunction.
HL 12.26 Mo 16:30 Poster A
Asymptotic analysis of radiation pattern of a classical dipole in
a photonic crystal — •Dmitry Chigrin and Clivia Sotomayor
Torres — Institute of Materials Science and Department of Electrical,
Information and Media Engineering, University of Wuppertal, D-42097
Wuppertal, Germany
Photonic crystals (PhCs) possess a complicated photonic band structure,
where allowed bands display strong dispersion and anisotropy. Recently,
there has been a growing interest in studies of energy flow inside
PhCs. Being a strongly anisotropic material, a PhC displays the beam
steering effect: the group velocity direction does not necessarily coincide
with the wavevector direction. As a consequence, the emission of an optically
active material placed within a PhC can reveal unusual properties.
In this contribution, an asymptotic analysis of the electromagnetic
field of a classical point dipole situated in PhC possessing an incomplete
bandgap is presented. The simple formula to calculate an angular distribution
of radiated power is introduced. Redistribution of the radiated
power is predicted. Within given approximation, the radiated power becomes
infinite in certain directions. These are directions in which the
direction of the group velocity of the crystal eigenmodes is stationary
with respect to a small variation in the wavevector direction. Predictions
of asymptotic analysis are substantiated with FTDT calculation.
HL 12.27 Mo 16:30 Poster A
Dynamics and entanglement of photon pulses in a photonic
crystal — Geesche Boedecker and •Carsten Henkel — Institut
für Physik, Universität Potsdam
In a photonic crystal, the dispersion relation of light can be tailored to
a great extent. Close to a band edge, for example, the group velocity is
significantly reduced. For a finite crystal slab, multiple reflections from
the end faces lead to a transmitted pulse train. We discuss the entanglement
properties of the transmitted pulses. The pulse shape inside the
crystal is analyzed for a one-dimensional model [1] in the regime of small
group velocities.
[1] Opt. Express 11 (2003) 1590