Light transport in macroporous gallium phosphide, perhaps the strongest nonabsorbing scatterer of visible light, is studied using phase-sensitive femtosecond pulse interferometry. Phase statistics are measured at optical wavelengths in both reflection and transmission and compared with theory. The diffusion constant of light is measured in both reflection and transmission as a function of thickness and compared with theories for diffusive transport and localization. An unusually high energy velocity due to the bicontinuous structure of the porous network is reported. For such strongly scattering samples, we show that surface properties and the effective index of refraction need to be treated carefully.
Light transport in a strongly scattering, strongly anisotropic material is studied experimentally using both static and time-resolved techniques. Both the static and the dynamic results are well characterized by a diffusion equation with an anisotropic diffusion tensor and a scalar absorption term. Light diffuses 4.0 times faster along the uniaxial axis of the material compared with diffusion in the orthogonal directions.
The enhanced backscattering cone displaying a strong anisotropy from a material with anisotropic diffusion is reported. The constructive interference of the wave is preserved in the helicity preserving polarization channel and completely lost in the nonpreserving one. The internal reflectivity at the interface modifies the width of the backscatter cone. The reflectivity coefficient is measured by angular-resolved transmission. This interface property is found to be isotropic, simplifying the backscatter cone analysis. The material used is a macroporous semiconductor, gallium phosphide, in which pores are etched in a disordered position but with a preferential direction.
We describe a method to couple a light pulse into a cavity with arbitrarily high finesse, with an efficiency that in theory can approach 100% even if the pulse duration is much longer than the round-trip time of the cavity. The spectrum of the pulse is compressed into a single narrow mode in an adiabatic and reversible way. The method uses an input coupler with a variable effective reflectivity which is adapted to match the known temporal shape of the pulse. In addition to a theoretical description of the method, we demonstrate the principle experimentally.
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