4,018 research outputs found
Vector Area Theorem mapping in crystals and polarization stability of SIT-solitons
The stability of polarization, areas, and number of self-induced transparency
(SIT)-solitons at the output from the LaF_3:Pr^{3+} crystal is theoretically
studied versus the polarization direction and the area of the input linearly
polarized laser pulse. For this purpose the Vector Area Theorem is rederived
and two-dimensional Vector Area Theorem map is obtained. The map is governed by
the crystal symmetry and takes into account directions of the dipole matrix
element vectors of the different site subgroups of optically excited ions. The
Vector Area Theorem mapping of the time evolution of the laser pulse allows one
to highlight soliton polarization properties.Comment: 3 pages, 3 figures; v2: minor corrected labels in Fig. 3 and its
cuptur
Low-Threshold Electrically Pumps Vertical-Cavity Surface-Emitting Microlasers
Vertical-cavity electrically driven lasers with three GaInAs
quantum wells and diameters of several ÎŒm exhibit room-temperature pulsed current thresholds as low as 1.3mA with 958 nm output wavelength
Room-Temperature Continuous-Wave Vertical-Cavity Single-Quantum-Well Microlaser Diodes
Room-temperature continuous and pulsed lasing of vertical-cavity, single-quantum-well, surface-emitting microlasers is achieved at ~983nm. The active Ga[sub][0-8]In[sub][0-2]As single quantum well is 100 [angstroms] thick. These microlasers have the smallest gain medium volumes among lasers ever built. The entire laser structure is grown by molecular beam epitaxy and the microlasers are formed by chemically assisted ion-beam etching. The microlasers are 3-50-ÎŒm across. The minimum threshold currents are 1.1 mA (pulsed) and 1.5 mA (CW)
Stress relaxation in F-actin solutions by severing
Networks of filamentous actin (F-actin) are important for the mechanics of
most animal cells. These cytoskeletal networks are highly dynamic, with a
variety of actin-associated proteins that control cross-linking, polymerization
and force generation in the cytoskeleton. Inspired by recent rheological
experiments on reconstituted solutions of dynamic actin filaments, we report a
theoretical model that describes stress relaxation behavior of these solutions
in the presence of severing proteins. We show that depending on the kinetic
rates of assembly, disassembly, and severing, one can observe both
length-dependent and length-independent relaxation behavior
Massive creation of entangled exciton states in semiconductor quantum dots
An intense laser pulse propagating in a medium of inhomogeneously broadened
quantum dots massively creates entangled exciton states. After passage of the
pulse all single-exciton states remain unpopulated (self-induced transparency)
whereas biexciton coherence (exciton entanglement) is generated through
two-photon transitions. We propose several experimental techniques for the
observation of such unexpected behavior
Strongly Localized State of a Photon at the Intersection of the Phase Slips in 2D Photonic Crystal with Low Contrast of Dielectric Constant
Two-dimensional photonic crystal with a rectangular symmetry and low contrast
(< 1) of the dielectric constant is considered. We demonstrate that, despite
the {\em absence} of a bandgap, strong localization of a photon can be achieved
for certain ``magic'' geometries of a unit cell by introducing two
phase slips along the major axes. Long-living photon mode is bound to the
intersection of the phase slips. We calculate analytically the lifetime of this
mode for the simplest geometry -- a square lattice of cylinders of a radius,
. We find the magic radius, , of a cylinder to be 43.10 percent of the
lattice constant. For this value of , the quality factor of the bound mode
exceeds . Small () deviation of from results in a
drastic damping of the bound mode.Comment: 6 pages, 2 figure
Spectropolarimetry of the Type IIb Supernova 2001ig
We present spectropolarimetric observations of the Type IIb SN 2001ig in NGC
7424; conducted with the ESO VLT FORS1 on 2001 Dec 16, 2002 Jan 3 and 2002 Aug
16 or 13, 31 and 256 days post-explosion. These observations are at three
different stages of the SN evolution: (1) The hydrogen-rich photospheric phase,
(2) the Type II to Type Ib transitional phase and (3) the nebular phase. At
each of these stages, the observations show remarkably different polarization
properties as a function of wavelength. We show that the degree of interstellar
polarization is 0.17%. The low intrinsic polarization (~0.2%) at the first
epoch is consistent with an almost spherical (<10% deviation from spherical
symmetry) hydrogen dominated ejecta. Similar to SN 1987A and to Type IIP SNe, a
sharp increase in the degree of the polarization (~1%) is observed when the
outer hydrogen layer becomes optically thin by day 31; only at this epoch is
the polarization well described by a ``dominant axis.'' The polarization angle
of the data shows a rotation through ~40 degrees between the first and second
epochs, indicating that the asymmetries of the first epoch were not directly
coupled with those observed at the second epoch. For the most polarized lines,
we observe wavelength-dependent loop structures in addition to the dominant
axis on the Q-U plane. We show that the polarization properties of Type IIb SNe
are roughly similar to one another, but with significant differences arising
due to line blending effects especially with the high velocities observed for
SN 2001ig. This suggests that the geometry of SN 2001ig is related to SN 1993J
and that these events may have arisen from a similar binary progenitor system.Comment: 42 pages, 12 figures (figs. 11 and 12 are both composed of four
subpanels, figs. 6,7,8,11 and 12 are in color, fig. 1 is low res and a high
res version is available at http://www.as.utexas.edu/~jrm/), ApJ Accepte
QED for a Fibrillar Medium of Two-Level Atoms
We consider a fibrillar medium with a continuous distribution of two-level
atoms coupled to quantized electromagnetic fields. Perturbation theory is
developed based on the current algebra satisfied by the atomic operators. The
one-loop corrections to the dispersion relation for the polaritons and the
dielectric constant are computed. Renormalization group equations are derived
which demonstrate a screening of the two-level splitting at higher energies.
Our results are compared with known results in the slowly varying envelope and
rotating wave approximations. We also discuss the quantum sine-Gordon theory as
an approximate theory.Comment: 32 pages, 4 figures, uses harvmac and epsf. In this revised version,
infra-red divergences are more properly handle
Directional interacting whispering gallery modes in coupled dielectric microdisks
We study the optical interaction in a coupled dielectric microdisks by
investigating the splitting of resonance positions of interacting whispering
gallery modes (WGMs) and their pattern change, depending on the distance
between the microdisks. It is shown that the interaction between the WGMs with
odd parity about y-axis becomes appreciable at a distance less than a
wavelength and causes directional emissions of the resulting interacting WGMs.
The directionality of the interacting WGMs can be understood in terms of an
effective boundary deformation in ray dynamical analysis. We also discuss about
the oscillation of the splitting when the distance is greater than a
wavelength.Comment: 7 pages, 10 figure
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