157 research outputs found
Effect of input pulse chirp on nonlinear energy deposition and plasma excitation in water
We analyze numerically and experimentally the effect of the input pulse chirp
on the nonlinear energy deposition from J fs-pulses at nm to
water. Numerical results are also shown for pulses at nm, where linear
losses are minimized, and for different focusing geometries. Input chirp is
found to have a big impact on the deposited energy and on the plasma
distribution around focus, thus providing a simple and effective mechanism to
tune the electron density and energy deposition. We identify three relevant
ways in which plasma features may be tuned.Comment: 9 pages, 7 figure
Study of ortho-to-paraexciton conversion in CuO by excitonic Lyman spectroscopy
Using time-resolved - excitonic Lyman spectroscopy, we study the
orthoexciton-to-paraexcitons transfer, following the creation of a high density
population of ultracold orthoexcitons by resonant two-photon excitation
with femtosecond pulses.
An observed fast exciton-density dependent conversion rate is attributed to
spin exchange between pairs of orthoexcitons.
Implication of these results on the feasibility of BEC of paraexcitons in
CuO is discussed
Bose-Einstein Condensation of Excitons: Reply to Tikhodeev's Criticism
The extended version of our reply to Comment on ``Critical Velocities in
Exciton Superfluidity'' by S. G. Tikhodeev (Phys. Rev. Lett., 84 (2000), 3502
or from http://prl.aps.org/) is presented here. The principal question is
discussed: does the moving exciton-phonon packet contain the coherent
`nucleus', or the exciton-phonon condensate?Comment: 3 pages in LaTe
Auger decay, Spin-exchange, and their connection to Bose-Einstein condensation of excitons in Cu_2O
In view of the recent experiments of O'Hara, et al. on excitons in Cu_2O, we
examine the interconversion between the angular-momentum triplet-state excitons
and the angular-momentum singlet-state excitons by a spin-exchange process
which has been overlooked in the past. We estimate the rate of this
particle-conserving mechanism and find a substantially higher value than the
Auger process considered so far. Based on this idea, we give a possible
explanation of the recent experimental observations, and make certain
predictions, with the most important being that the singlet-state excitons in
Cu_2O is a very serious candidate for exhibiting the phenomenon of
Bose-Einstein condensation.Comment: 4 pages, RevTex, 1 ps figur
Exciton–biexciton quantum coherence and polaritonic stop-band transparency in CuCl.
A coherently driven exciton-biexciton transition in CuCl enables one to propagate a probe light beam within the exciton-polariton stop-band where radiation is otherwise completely reflected. The stop-band transparency window can be controlled via the pump beam frequency and intensity. The phenomenon is reminiscent of quantum coherence effects occurring in three-level atomic systems, except that it here involves delocalized electronic excitations in a crystal via a frequency and wave-vector selective polaritonic mechanism. Both a free standing slab and a microcavity configuration are theoretically studied
Auger decay of degenerate and Bose-condensed excitons in CuO
We study the non-radiative Auger decay of excitons in CuO, in which two
excitons scatter to an excited electron and hole. The exciton decay rate for
the direct and the phonon-assisted processes is calculated from first
principles; incorporating the band structure of the material leads to a
relatively shorter lifetime of the triplet state ortho excitons. We compare our
results with the Auger decay rate extracted from data on highly degenerate
triplet excitons and Bose-condensed singlet excitons in CuO.Comment: 15 pages, revtex, figures available from G. Kavoulaki
Polaritonic stop-band transparency via exciton-biexciton coupling in CuCl
Radiation is almost completely reflected within the exciton-polariton stop band of a semiconductor, as in the typical case of CuCl. We predict, however, that a coherently driven exciton-biexciton transition allows for the propagation of a probe light beam within the stop band. The phenomenon is reminiscent of electromagnetically induced transparency effects occurring in three-level atomic systems, except that it here involves delocalized electronic excitations in a crystalline structure via a frequency and wave-vector selective polaritonic mechanism. A well-developed transparency, favored by the narrow linewidth of the biexciton, is established within the stop band where a probe pulse may propagate with significant delays. The transparency window can be controlled via the pump beam detuning and intensity
On Critical Velocities in Exciton Superfluidity
The presence of exciton phonon interactions is shown to play a key role in
the exciton superfluidity. We apply the Landau criterion for an exciton-phonon
condensate moving uniformly at zero temperature. It turns out that there are
essentially two critical velocities in the theory. Within the range of these
velocities the condensate can exist only as a bright soliton. The excitation
spectrum and differential equations for the wave function of this condensate
are derived.Comment: 7 pages, Latex; to be published in Phys.Rev.Lett (1997
Stress Dependence of Exciton Relaxation Processes in Cu2O
A comprehensive study of the exciton relaxation processes in Cu2O has led to
some surprises. We find that the ortho-para conversion rate becomes slower at
high stress, and that the Auger nonradiative recombination rate increases with
stress, with apparently no Auger recombination at zero stress. These results
have important consequences for the pursuit of Bose-Einstein condensation of
excitons in a harmonic potential.Comment: 10 figures, 1 tabl
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