99 research outputs found
Anomalous transient amplification of waves in non-normal photonic media
Dissipation is a ubiquitous phenomenon in dynamical systems encountered in
nature because no finite system is fully isolated from its environment. In
optical systems, a key challenge facing any technological application has
traditionally been the mitigation of optical losses. Recent work has shown that
a new class of optical materials that consist of a precisely balanced
distribution of loss and gain can be exploited to engineer novel
functionalities for propagating and filtering electromagnetic radiation. Here
we show a generic property of optical systems that feature an unbalanced
distribution of loss and gain, described by non-normal operators, namely that
an overall lossy optical system can transiently amplify certain input signals
by several orders of magnitude. We present a mathematical framework to analyze
the dynamics of wave propagation in media with an arbitrary distribution of
loss and gain and construct the initial conditions to engineer such non-normal
power amplifiers. Our results point to a new design space for engineered
optical systems employed in photonics and quantum optics.Comment: 11 pages, 11 figure
Interaction-induced mode switching in steady-state microlasers
We demonstrate that due to strong modal interactions through cross-gain
saturation, the onset of a new lasing mode can switch off an existing mode via
a negative power slope. In this process of interaction-induced mode switching
(IMS) the two involved modes maintain their identities, i.e. they do not change
their spatial field patterns or lasing frequencies. For a fixed pump profile, a
simple analytic criterion for the occurrence of IMS is given in terms of their
self- and cross-interaction coefficients and non-interacting thresholds, which
is verified for the example of a two-dimensional microdisk laser. When the
spatial pump profile is varied as the pump power is increased, IMS can be
induced even when it would not occur with a fixed pump profile, as we show for
two coupled laser cavities. Our findings apply to steady-state lasing and are
hence different from dynamical mode switching or hopping. IMS may have
potential applications in robust and flexible all-optical switching.Comment: 14 pages, 5 figure
Polarization properties and dispersion relations for spiral resonances of a dielectric rod
Dielectric microcavities based on cylindrical and deformed cylindrical shapes
have been employed as resonators for microlasers. Such systems support spiral
resonances with finite momentum along the cylinder axis. For such modes the
boundary conditions do not separate and simple TM and TE polarization states do
not exist. We formulate a theory for the dispersion relations and polarization
properties of such resonances for an infinite dielectric rod of arbitrary
cross-section and then solve for these quantities for the case of a circular
cross-section (cylinder). Useful analytic formulas are obtained using the
eikonal (Einstein-Brillouin-Keller) method which are shown to be excellent
approximations to the exact results from the wave equation. The major finding
is that the polarization of the radiation emitted into the far-field is linear
up to a polarization critical angle (PCA) at which it changes to elliptical.
The PCA always lies between the Brewster and total-internal-reflection angles
for the dielectric, as is shown by an analysis based on the Jones matrices of
the spiraling rays.Comment: submitted to JOSA
Chaos-assisted emission from asymmetric resonant cavity microlasers
We study emission from quasi-one-dimensional modes of an asymmetric resonant
cavity that are associated with a stable periodic ray orbit confined inside the
cavity by total internal reflection. It is numerically demonstrated that such
modes exhibit directional emission, which is explained by chaos-assisted
emission induced by dynamical tunneling. Fabricating semiconductor microlasers
with the asymmetric resonant cavity, we experimentally demonstrate the
selective excitation of the quasi-one-dimensional modes by employing the device
structure to preferentially inject currents to these modes and observe
directional emission in good accordance with the theoretical prediction based
on chaos-assisted emission.Comment: 9 pages, 10 figures, some figures are in reduced qualit
Fresnel filtering in lasing emission from scarred modes of wave-chaotic optical resonators
We study lasing emission from asymmetric resonant cavity (ARC) GaN
micro-lasers. By comparing far-field intensity patterns with images of the
micro-laser we find that the lasing modes are concentrated on three-bounce
unstable periodic ray orbits, i.e. the modes are scarred. The high-intensity
emission directions of these scarred modes are completely different from those
predicted by applying Snell's law to the ray orbit. This effect is due to the
process of ``Fresnel filtering'' which occurs when a beam of finite angular
spread is incident at the critical angle for total internal reflection.Comment: 4 pages, 3 figures (eps), RevTeX 3.1, submitted to Phys. Rev. Lett;
corrected a minor (transcription) erro
Self-consistent multi-mode lasing theory for complex or random lasing media
A semiclassical theory of single and multi-mode lasing is derived for open
complex or random media using a self-consistent linear response formulation.
Unlike standard approaches which use closed cavity solutions to describe the
lasing modes, we introduce an appropriate discrete basis of functions which
describe also the intensity and angular emission pattern outside the cavity.
This constant flux (CF) basis is dictated by the Green function which arises
when formulating the steady state Maxwell-Bloch equations as a self-consistent
linear response problem. This basis is similar to the quasi-bound state basis
which is familiar in resonator theory and it obeys biorthogonality relations
with a set of dual functions. Within a single-pole approximation for the Green
function the lasing modes are proportional to these CF states and their
intensities and lasing frequencies are determined by a set of non-linear
equations. When a near threshold approximation is made to these equations a
generalized version of the Haken-Sauermann equations for multi-mode lasing is
obtained, appropriate for open cavities. Illustrative results from these
equations are given for single and few mode lasing states, for the case of
dielectric cavity lasers. The standard near threshold approximation is found to
be unreliable. Applications to wave-chaotic cavities and random lasers are
discussed.Comment: 18 pages, 9 figure
Dramatic Shape Sensitivity of Directional Emission Patterns from Similarly Deformed Cylindrical Polymer Lasers
Recent experiments on similarly shaped polymer micro-cavity lasers show a
dramatic difference in the far-field emission patterns. We show for different
deformations of the ellipse, quadrupole and hexadecapole that the large
differences in the far-field emission patterns is explained by the differing
ray dynamics corresponding to each shape. Analyzing the differences in the
appropriate phase space for ray motion, it is shown that the differing
geometries of the unstable manifolds of periodic orbits are the decisive
factors in determining the far-field pattern. Surprisingly, we find that
strongly chaotic ray dynamics is compatible with highly directional emission in
the far-field.Comment: 14 pages, 16 figures (eps), RevTeX 4, submitted to JOSA
Interaction quench dynamics in the Kondo model in presence of a local magnetic field
In this work we investigate the quench dynamics in the Kondo model on the
Toulouse line in presence of a local magnetic field. It is shown that this
setup can be realized by either applying the local magnetic field directly or
by preparing the system in a macroscopically spin-polarized initial state. In
the latter case, the magnetic field results from a subtlety in applying the
bosonization technique where terms that are usually referred to as finite-size
corrections become important in the present non-equilibrium setting. The
transient dynamics is studied by analyzing exact analytical results for the
local spin dynamics. The time scale for the relaxation of the local dynamical
quantities turns out to be exclusively determined by the Kondo scale. In the
transient regime, one observes damped oscillations in the local correlation
functions with a frequency set by the magnetic field.Comment: 8 pages, 2 figures; minor changes, version as publishe
Expression of testicular genes in haematological malignancies
The gene expression of a new group of tumour antigens known as cancer/testis (CT) antigens is now well-recognized in some solid tumours. However, their expression in haematological malignancies remained unclear. In this study, we have used reverse transcription polymerase chain reaction and Southern blot analysis to examine the presence of transcripts for the three CT antigens, NY-ESO-1, SSX2 and SCP1 in haematological malignant cells. We found that transcripts for SCP1 could be detected in 10% of myeloma, 5.7% of acute myeloid leukaemia and 23% of chronic myeloid leukaemia. In contrast, NY-ESO-1 and SSX2 were not detected in any of the 107 tumour samples. © 1999 Cancer Research Campaig
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