50 research outputs found
Intense ultra-broadband down-conversion from randomly poled nonlinear crystals
Randomly poled nonlinear crystals are shown to be able to emit intense
ultra-broadband photon-pair fields with properties comparable to those coming
from chirped periodically-poled crystals. Their intensities scale linearly with
the number of domains. Also photon pairs extending over intervals with
durations comparable to one optical cycle can be generated in these crystals.Comment: 6 pages, 4 figure
Experimental observation of second-harmonic generation and diffusion inside random media
We have experimentally measured the distribution of the second-harmonic
intensity that is generated inside a highly-scattering slab of porous gallium
phosphide. Two complementary techniques for determining the distribution are
used. First, the spatial distribution of second-harmonic light intensity at the
side of a cleaved slab has been recorded. Second, the total second-harmonic
radiation at each side of the slab has been measured for several samples at
various wavelengths. By combining these measurements with a diffusion model for
second-harmonic generation that incorporates extrapolated boundary conditions,
we present a consistent picture of the distribution of the second-harmonic
intensity inside the slab. We find that the ratio of the
mean free path at the second-harmonic frequency to the coherence length, which
was suggested by some earlier calculations, cannot describe the second-harmonic
yield in our samples. For describing the total second-harmonic yield, our
experiments show that the scattering parameter at the fundamental frequency
\k_{1\omega}\ell_{1\omega} is the most relevant parameter in our type of
samples.Comment: 10 pages, 7 figure
Resonant second harmonic generation in random dielectric structures
International audience; We show that resonant second harmonic generation can be obtained in random dielectric structures. The scheme is based on internal resonances due to the optical counterpart of Anderson localization. By making use of different localization lengths at the fundamental and at the second harmonic frequencies, we predict a conversion efficiency that is four orders of magnitude higher than a bulk material and even one order of magnitude higher than an ideal phase matched slab of the same size. The method is highly insensitive to fabrication tolerances, and provides excellent angle tunability. [DOI:10.2971/jeos.2006.06021
Emission of photon echoes in a strongly scattering medium
We observe the two- and three-pulse photon echo emission from a scattering
powder, obtained by grinding a Pr:YSiO rare earth doped single
crystal. We show that the collective emission is coherently constructed over
several grains. A well defined atomic coherence can therefore be created
between randomly placed particles. Observation of photon echo on powders as
opposed to bulk materials opens the way to faster material development. More
generally, time-domain resonant four-wave mixing offers an attractive approach
to investigate coherent propagation in scattering media
Mapping of periodically poled crystals via spontaneous parametric down-conversion
A new method for characterization of periodically poled crystals is developed
based on spontaneous parametric down-conversion. The method is demonstrated on
crystals of Y:LiNbO3, Mg:Y:LiNbO3 with non-uniform periodically poled
structures, obtained directly under Czochralski growth procedure and designed
for application of OPO in the mid infrared range. Infrared dispersion of
refractive index, effective working periods and wavelengths of OPO were
determined by special treatment of frequency-angular spectra of spontaneous
parametric down-conversion in the visible range. Two-dimensional mapping via
spontaneous parametric down-conversion is proposed for characterizing spatial
distribution of bulk quasi-phase matching efficiency across the input window of
a periodically poled sample.Comment: 19 pages, 6 figure
Nonlinear effects in random lasers
Recent numerical and theoretical studies have demonstrated that the modes at
threshold of a random laser are in direct correspondence with the resonances of
the same system without gain, a feature which is well known in a conventional
laser but which was not known until recently for a random laser. This paper
presents numerical results, which extend such studies to the multimode regime
that takes place when the pumping rate is progressively increased above
threshold. Behavior that is already known in standard lasers, such as mode
competition and nonlinear wave-mixing, are shown to also take place in random
lasers thus reinforcing their recent modal description. However, due to the
complexity of the laser modes and to the openness of such lasers, which
requires large external pumping to compensate for strong loss, one observes
that these effects are more pronounced than in a conventional laser