10 research outputs found
Atom holography
We study the conditions under which atomic condensates can be used as a
recording media and then suggest a reading scheme which allows to reconstruct
an object with atomic reading beam. We show that good recording can be achieved
for flat condensate profiles and for negative detunings between atomic Bohr
frequency and optical field frequency. The resolution of recording dramatically
depends on the relation between the healing length of the condensate and the
spatial frequency contents of the optical fields involved.Comment: 8 pages, 5 figures, Late
Unbound states in quantum heterostructures
We report in this review on the electronic continuum states of semiconductor Quantum Wells and Quantum Dots and highlight the decisive part played by the virtual bound states in the optical properties of these structures. The two particles continuum states of Quantum Dots control the decoherence of the excited electron – hole states. The part played by Auger scattering in Quantum Dots is also discussed
Dynamic Acoustic Control of Individual Optically Active Quantum Dot-like Emission Centers in Heterostructure Nanowires
We probe and control the optical properties of emission centers forming in
radial het- erostructure GaAs-Al0.3Ga0.7As nanowires and show that these
emitters, located in Al0.3Ga0.7As layers, can exhibit quantum-dot like
characteristics. We employ a radio frequency surface acoustic wave to
dynamically control their emission energy and occupancy state on a nanosec- ond
timescale. In the spectral oscillations we identify unambiguous signatures
arising from both the mechanical and electrical component of the surface
acoustic wave. In addition, differ- ent emission lines of a single quantum dot
exhibit pronounced anti-correlated intensity oscilla- tions during the acoustic
cycle. These arise from a dynamically triggered carrier extraction out of the
quantum dot to a continuum in the radial heterostructure. Using finite element
modeling and Wentzel-Kramers-Brillouin theory we identify quantum tunneling as
the underlying mech- anism. These simulation results quantitatively reproduce
the observed switching and show that in our systems these quantum dots are
spatially separated from the continuum by > 10.5 nm.Comment: This document is the unedited Author's version of a Submitted Work
that was subsequently accepted for publication in Nano Letters, copyright
\c{copyright} American Chemical Society after peer review. To access the
final edited and published work see
http://pubs.acs.org/doi/abs/10.1021/nl404043
Development of a transfer standard for laser thermometry
The measurement of gas temperatures is important in many combustion, chemical manufacturing and materials processing applications. Different laser spectroscopic methods are applied to measure the temperature of gases. Nevertheless, up to now none of these methods have been calibrated against the international temperature scale of 1990 (ITS-90). A transfer standard for laser thermometry (TSL) has been developed to calibrate laser thermometry techniques. The standard provides optical access to a sample volume of a gas maintained at a stable temperature within the range of 300 K to 1850 K. The gas temperature is measured using built-in, calibrated thermometers including thermocouples, Accufiber optical-fibre probes and an optical pyrometer for traceability to the ITS-90. Broadband Coherent Anti-Stokes Raman Scattering (CARS) and scanning CARS experiments have been performed inside the furnace. The measuring uncertainty of broadband CARS amounts to less than 4 per cent between room tempera ture and 800 K. At temperatures between 800 K and 1850 K an uncertainty of less than 2 per cent has been achieved. For scanning CARS the uncertainty and the precision amounts to 2 per cent between 295 K and 1850 K