Complex Quantum Systems/Condensed Matter Seminar

Prof. A. Douglas Stone, Yale University

"Random and Chaotic Lasers: Why They’re Interesting and What They’re Good For"

12:30pm, RLM 11.204

Abstract: Random and wave-chaotic lasers challenge the prevailing conceptual framework of laser physics since their lasing modes cannot be understood by a semiclassical ray interference picture.  In addition, they are typically highly open systems, unlike conventional cavities, which in many cases have passive cavity finesse less than unity, implying that they support no measurable resonances in linear scattering.  Hence one cannot think of the lasing modes as simply equivalent to passive cavity resonances enhanced with sufficient gain to self-oscillate.  Understanding such lasers fully required a generalization of the standard semiclassical laser theory, which has been achieved via Steady-state Ab Initio Laser Theory (SALT).  This is a set of self-consistent non-linear and non-hermitian wave equations for the multimode steady-state of a laser system, which determines the exact solution of the laser equations in a large and physically relevant parameter range. These equations provide great insight into the physics of random and chaotic lasers. In addition, the SALT equations are significantly more computationally tractable than brute force FDTD methods, and are therefore make it practical to treat spatially complex and random lasers, where one is typically interested in the statistical properties of an ensemble of lasers, and not one specific cavity design.  Moreover, the equations can be treated analytically for random lasers in the interesting two and three-dimensional cases.  I will report results from a rigorous SALT-based statistical theory of random and chaotic lasers. A property of random and chaotic lasers is that many of the lasing modes have similar linear thresholds, leading to highly multimode lasing.  Light emitted from such lasers thus has a relatively low degree of spatial coherence and can be used as a unique, high photon degeneracy light source for imaging applications.  This has been demonstrated recently for both random and chaotic laser systems.