1,865 research outputs found
Spontaneous emission of a nanoscopic emitter in a strongly scattering disordered medium
Fluorescence lifetimes of nitrogen-vacancy color centers in individual
diamond nanocrystals were measured at the interface between a glass substrate
and a strongly scattering medium. Comparison of the results with values
recorded from the same nanocrystals at the glass-air interface revealed
fluctuations of fluorescence lifetimes in the scattering medium. After
discussing a range of possible systematic effects, we attribute the observed
lengthening of the lifetimes to the reduction of the local density of states.
Our approach is very promising for exploring the strong three-dimensional
localization of light directly on the microscopic scale.Comment: 9 pages, 4 figure
Vibrational spectroscopy of H2+: precise evaluation of the Zeeman effect
We present an accurate computation of the g-factors of the hyperfine states
of the hydrogen molecular ion H2+. The results are in good agreement with
previous experiments, and can be tested further by rf spectroscopy. Their
implication for high-precision two-photon vibrational spectroscopy of H2+ is
also discussed. It is found that the most intense hyperfine components of
two-photon lines benefit from a very small Zeeman splitting
Effect of nuclear motion on the critical nuclear charge for two-electron atoms
A variational method for calculating the critical nuclear charge, Zc, required for the binding of a nucleus to two electrons is reported. The method is very effective and performs well compared to the traditional variational principle for calculating energy. The critical nuclear charge, which corresponds to the minimum charge required for the atomic system to have at least one bound state, has been calculated for helium-like systems both with infinite and finite nuclear masses. The value of 0.911 028 2(3) is in very good agreement with recent values in the literature for two-electron atoms with an infinite nuclear mass. When nuclear motion is considered, the value for Zc varies from 0.911 030 3(2) for that with a nuclear mass of Ne (the largest heliogenic system considered) to 0.921 802 4(4) for a system with the nuclear mass of a positron. In all cases the energy varies smoothly as . It is found that for the finite nuclear mass case, in agreement with previous work for the fixed nucleus mass system, the outer electron remains localised near the nucleus at Z = Zc. Additionally, the electron probability distribution is calculated to determine the behaviour of the electrons at low Z
Excitonic Dynamical Franz-Keldysh Effect
The Dynamical Franz-Keldysh Effect is exposed by exploring near-bandgap
absorption in the presence of intense THz electric fields. It bridges the gap
between the DC Franz- Keldysh effect and multi-photon absorption and competes
with the THz AC Stark Effect in shifting the energy of the excitonic resonance.
A theoretical model which includes the strong THz field non-perturbatively via
a non-equilibrium Green Functions technique is able to describe the Dynamical
Franz-Keldysh Effect in the presence of excitonic absorption.Comment: 4 pages in revtex with 5 figures included using epsf. Submitted to
Physical Review Letter
FAST CARS: Engineering a Laser Spectroscopic Technique for Rapid Identification of Bacterial Spores
Airborne contaminants, e.g., bacterial spores, are usually analyzed by time
consuming microscopic, chemical and biological assays. Current research into
real time laser spectroscopic detectors of such contaminants is based on e.g.
resonant Raman spectroscopy. The present approach derives from recent
experiments in which atoms and molecules are prepared by one (or more) coherent
laser(s) and probed by another set of lasers. The connection with previous
studies based on "Coherent Anti-Stokes Raman Spectroscopy" (CARS) is to be
noted. However generating and utilizing maximally coherent oscillation in
macromolecules having an enormous number of degrees of freedom is much more
challenging. This extension of the CARS technique is called FAST CARS
(Femtosecond Adaptive Spectroscopic Techniques for Coherent Anti-Stokes Raman
Spectroscopy), and the present paper proposes and analyses ways in which it
could be used to rapidly identify pre-selected molecules in real time.Comment: 43 pages, 21 figures; replacement with references added. Submitted to
the Proceedings of National Academy of Science
Angular regularities of the photon echo in doped crystals
The regularities of the two-pulse photon echo generation in doped crystals under changes in the angle a between directions of propagation of pumping pulses are investigated theoretically. The explanation of some experimental results obtained by U.P. Wild and coworkers, in particular, the modulation character of the response-intensity dependence on the angle a is presented. Copyright © 1996 by MANK Hayka/Interperiodica Publishing
Spatial and spectral properties of a photon echo
Spatial and spectral regularities in the formation of photon echo signals are studied. The frequency shift of the signal of a primary photon echo with respect to the carrier frequency of excitation laser pulses that was experimentally observed upon variation of the angle between the wave vectors of the laser pulses is explained. The feasibility of high-resolution angular optical echo spectroscopy is shown
Angular regularities of the photon echo in doped crystals
The regularities of the two-pulse photon echo generation in doped crystals under changes in the angle a between directions of propagation of pumping pulses are investigated theoretically. The explanation of some experimental results obtained by U.P. Wild and coworkers, in particular, the modulation character of the response-intensity dependence on the angle a is presented. Copyright © 1996 by MANK Hayka/Interperiodica Publishing
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