717 research outputs found
Spatial Solitons in Media with Delayed-Response Optical Nonlinearities
Near-soliton scanning light-beam propagation in media with both
delayed-response Kerr-type and thermal nonlinearities is analyzed. The
delayed-response part of the Kerr nonlinearity is shown to be competitive as
compared to the thermal nonlinearity, and relevant contributions to a
distortion of the soliton form and phase can be mutually compensated. This
quasi-soliton beam propagation regime keeps properties of the incli- ned
self-trapped channel.Comment: 7 pages, to be published in Europhys. Let
Polarization-squeezed light formation in a medium with electronic Kerr nonlinearity
We analyze the formation of polarization-squeezed light in a medium with
electronic Kerr nonlinearity. Quantum Stokes parameters are considered and the
spectra of their quantum fluctuations are investigated. It is established that
the frequency at which the suppression of quantum fluctuations is the greatest
can be controlled by adjusting the linear phase difference between pulses. We
shown that by varying the intensity or the nonlinear phase shift per photon for
one pulse, one can effectively control the suppression of quantum fluctuations
of the quantum Stokes parameters.Comment: final version, RevTeX, 10 pages, 5 eps figure
Ultranarrow resonance peaks in the transmission and reflection spectra of a photonic crystal cavity with Raman gain
The Raman gain of a probe light in a three-state -scheme placed
into a defect of a one-dimensional photonic crystal is studied theoretically.
We show that there exists a pump intensity range, where the transmission and
reflection spectra of the probe field exhibit \textit{simultaneously} occurring
narrow peaks (resonances) whose position is determined by the Raman resonance.
Transmission and reflection coefficients can be larger than unity at pump
intensities of order tens of W/cm. When the pump intensity is
outside this region, the peak in the transmission spectrum turns into a narrow
dip. The nature of narrow resonances is attributed to a drastic dispersion of
the nonlinear refractive index in the vicinity of the Raman transition, which
leads to a significant reduction of the group velocity of the probe wave.Comment: 9 pages, 3 figure
Universal shape law of stochastic supercritical bifurcations: Theory and experiments
A universal law for the supercritical bifurcation shape of transverse
one-dimensional (1D) systems in presence of additive noise is given. The
stochastic Langevin equation of such systems is solved by using a Fokker-Planck
equation leading to the expression for the most probable amplitude of the
critical mode. From this universal expression, the shape of the bifurcation,
its location and its evolution with the noise level are completely defined.
Experimental results obtained for a 1D transverse Kerr-like slice subjected to
optical feedback are in excellent agreement.Comment: 5 pages, 5 figure
Spatial Optical Solitons due to Multistep Cascading
We introduce a novel class of parametric optical solitons supported
simultaneously by two second-order nonlinear cascading processes,
second-harmonic generation and sum-frequency mixing. We obtain, analytically
and numerically, the solutions for three-wave spatial solitons and show that
the presence of an additional cascading mechanism can change dramatically the
properties and stability of two-wave quadratic solitary waves.Comment: 6 pages, 4 figure
High-sensitivity imaging with multi-mode twin beams
Twin entangled beams produced by single-pass parametric down-conversion (PDC)
offer the opportunity to detect weak amount of absorption with an improved
sensitivity with respect to standard techniques which make use of classical
light sources. We propose a differential measurement scheme which exploits the
spatial quantum correlation of type II PDC to image a weak amplitude object
with a sensitivity beyond the standard quantum limit imposed by shot-noise.Comment: 13 pages, 8 figure
Multistep cascading and fourth-harmonic generation
We apply the concept of multistep cascading to the problem of fourth-harmonic
generation in a single quadratic crystal. We analyze a new model of parametric
wave mixing and describe its stationary solutions for two- and three-color
plane waves and spatial solitons. Some applications to the optical frequency
division as well as the realization of the double-phase-matching processes in
engineered QPM structures with phase reversal sequences are also discussed.Comment: 3 pages, 3 figure
Soliton absorption spectroscopy
We analyze optical soliton propagation in the presence of weak absorption
lines with much narrower linewidths as compared to the soliton spectrum width
using the novel perturbation analysis technique based on an integral
representation in the spectral domain. The stable soliton acquires spectral
modulation that follows the associated index of refraction of the absorber. The
model can be applied to ordinary soliton propagation and to an absorber inside
a passively modelocked laser. In the latter case, a comparison with water vapor
absorption in a femtosecond Cr:ZnSe laser yields a very good agreement with
experiment. Compared to the conventional absorption measurement in a cell of
the same length, the signal is increased by an order of magnitude. The obtained
analytical expressions allow further improving of the sensitivity and
spectroscopic accuracy making the soliton absorption spectroscopy a promising
novel measurement technique.Comment: 9 pages, 7 figures
Optimal coherent control of CARS: signal enhancement and background elimination
The ability to enhance resonant signals and eliminate the non-resonant
background is analyzed for Coherent Anti-Stokes Raman Scattering (CARS). The
analysis is done at a specific frequency as well as for broadband excitation
using femtosecond pulse-shaping techniques. An appropriate objective functional
is employed to balance resonant signal enhancement against non-resonant
background suppression. Optimal enhancement of the signal and minimization of
the background can be achieved by shaping the probe pulse alone while keeping
the pump and Stokes pulses in transform-limited-form (TLF). In some cases
analytical forms for the probe pulse can be found, and numerical simulations
are carried out for other circumstances. It is found that a good approximate
solution for the optimal pulse in the two-pulse CARS is a superposition of
linear and arctangent type phases for the pump. The well-known probe delay
method is shown to be a quasi-optimal scheme for background suppression. The
results should provide a basis to improve the performance of CARS spectroscopy
and microscopy.Comment: 11 pages,10 figures, JC
Bose-Einstein condensation of magnons under incoherent pumping
Bose-Einstein condensation in a gas of magnons pumped by an incoherent
pumping source is experimentally studied at room temperature. We demonstrate
that the condensation can be achieved in a gas of bosons under conditions of
incoherent pumping. Moreover, we show the critical transition point is almost
independent of the frequency spectrum of the pumping source and is solely
determined by the density of magnons. The electromagnetic power radiated by the
magnon condensate was found to scale quadratically with the pumping power,
which is in accordance with the theory of Bose-Einstein condensation in magnon
gases
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