We demonstrate random lasing emission in an active planar slab of AlGaAs/GaAs randomly perforated with subwavelength circular holes. Spectrally-resolved imaging of both the diffusion in the passive regime together with the lasing emission allows identifying exteneded lasing modes in the weakly diffusive regime.
The first experimental evidence of speckle instability is realized by using a liquid crystal cell with a photosensitive
wall. The light is transversally scattered in the liquid crystal cell, where a two-dimensional controlled disorder is
imprinted through suitable illuminations of the photoconductive wall and the nonlinearity is obtained through
optical reorientation of the liquid crystal molecules. Above a critical threshold of the input intensity, the speckle
pattern starts spontaneously to oscillate with a characteristic frequency related to the response time of the
nonlinear medium. Moreover, the oscillation threshold depends on the scattering mean free path, thus, confirming
the crucial role played by disorder in inducing the instability.
We explore the specific nature of wave propagation in multiple scattering media and examine how this is revealed in
various aspects of the speckle pattern measured at the output surface of an ensemble of disordered media. We present
near-field measurements of the speckle pattern transmitted through random samples in a quasi-one dimensional
geometry. The microwave field -amplitude and phase- is measured as a function of frequency on a grid of points on the
output surface of samples composed of randomly positioned dielectric spheres. The field and intensity correlation
functions versus displacement and frequency shift are measured and reveal non-Gaussian behavior, namely long range
correlation. The widest fluctuations of the phase derivative with frequency are found at low intensity values near a phase
singularity in the transmitted speckle pattern. The position of these phase singularities at which the intensity vanishes is
reconstructed for the entire speckle pattern and followed in space while frequency is shifted.
In this paper, we explore the specific nature of wave propagation in multiple scattering media and examine how this is revealed in various aspects of the speckle pattern measured at the output surface of an ensemble of disordered media. We present near-field measurements of the speckle pattern transmitted through random samples in a quasi-one dimensional geometry. The microwave field--amplitude and phase--is measured as a function of frequency along perpendicular transverse polarizations on a close grid of points on the output surface of samples composed of randomly positioned dielectric spheres. The field spectrum is Fourier transformed to access the temporal evolution of the speckle pattern. The field and intensity correlation functions versus displacement and frequency shift are measured and reveal non-Gaussian behavior, namely long range correlation. The key distributions and correlation functions of the delay time are also measured and compared to calculations, to show the interplay between the delay time and the intensity in the speckle pattern. The widest fluctuations of the phase derivative with frequency are found at low intensity values near a phase singularity in the transmitted speckle pattern. The position of these phase singularities at which the intensity vanishes is reconstructed for the entire speckle pattern.
In this paper, we attempt to find a unified framework in which the statistics of wave propagation in random media can be understood as strengths of scattering and absorption increase. First, we discuss the weak scattering, diffusive limit without absorption. In this limit, the suppression of transmission by weak localization, the distribution of total transmission and the intensity correlation functions with displacement and polarization rotation are all described in terms of the dimensionless conductance so that these effects are explicitly linked. When absorption is introduced, the dimensionless conductance can no longer serve as a fundamental scaling parameter, but the variance of the total transmission is still able to chart the changing statistical character of propagation and localization with sample size. By examining transport at a fixed time following pulsed excitation, the affect of absorption can be removed while the growing impact of localization can be clearly discerned. The functional form of probability distributions of intensity and total transmission and of the spatial and polarization intensity correlation functions in the time domain are the same as in the frequency domain. The connection of mesoscopic fluctuations to localization can be seen in the spectral correlation function of the field, which is the Fourier transform of average pulsed transmission. The spectral field correlation function can be expressed as a product of the correlation function of the field normalized to the average amplitude in a given configuration and of the square root of the total transmission.
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