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Prof. Azriel Genack

“ Education is all a matter of building bridges. ”
- Ralph Ellison

For the last decade, Dr. Genack has been involved in the study of classical wave propagation in the presence of disorder. Both microwave (10 GHz to 20 GHz) and laser (630.8 nm) speckle patterns are studied in Dr. Genack's group. Some typical research projects are 1) 1-dimensional microwave system (10 GHz to 20 GHz); 2) quasi-1-dimensional microwave tube for speckle study (10 GHz to 15 GHz); and 3) He-Ne laser for deformed glass layers study.

Classical waves are the means by which we probe our environment and communicate with one another. As a result of wave - particle duality, studies of classical waves also serve as exacting models of electronic transport, involving quantum mechanical waves, in the solid state. One goal of studies at Queens College of optical and microwave radiation propagation is to provide a universal description of wave scattering in random systems. The Queens College group has demonstrated the relationship between the statistics of fluctuations of intensity and total transmission, non-local intensity correlation, and average transport in space, time, and frequency. This has provided essential models of electronic transport in mesoscopic systems, which are systems in which the phase coherence of the wave is preserved throughout the sample. Essential aspects of transport are described in terms of the degree of intensity correlation in space, which determines the closeness to the threshold for Anderson localization. Beyond the localization threshold, propagation is largely suppressed as a result of the interference of backscattered waves. The microwave laboratory was started in collaboration with Dr. Narciso Garcia. Many key measurements have been compared to theoretical calculations of Dr. A. A. Lisyansky and his students.

Among the milestones achieved in statistical studies have been the following: observations of short, long and infinite range intensity correlation in space and frequency; observation of the consequences of such correlation in producing marked and universal deviations of intensity and transmission distributions from their form for diffusive waves far from the localization threshold; observation of universal dynamical fluctuations in the dwell time of waves in random media; measurements of the statistical character of the transmitted field in the crossover from ballistic to diffusive propagation; creation of localized states in nearly periodic copper wire network filled with random mixtures of scattering particles; observations of resonances and in random media; and the inclusion of boundary effects to quantitatively describe transport. In addition acousto-optic tomography using diffuse light has been demonstrated, and Monte Carlo simulations of the random walk of photons in amplifying random media have established the incoherent nature of laser action in these systems.

In work carried out before coming to Queens College, Dr. Genack has demonstrated the diffusion of nuclear magnetism in superconductors, measured the spectrum of Wannier excitons in Cu2O, demonstrated the use of photochemical hole burning to measure the homogeneous linewidth of molecules in solids, developed methods of coherent transient spectroscopy such as frequency and phase switching which have clarified the loss of coherence in atoms, molecules and solids, and has demonstrated that the origin of surface enhanced Raman scattering from molecules on metal surfaces is the resonant excitation of plasmons associated with surface roughness.