Abstract:
Over a decade ago an overlooked symmetry of Maxwell’s equations coupled to matter was recognized, a relationship between a laser at threshold and a perfectly absorbing resonator. The threshold condition for lasing is the point at which gain balances loss, and the system self-organizes to oscillate coherently at a specific frequency in the highest Q electromagnetic mode. At this special point the system supports a purely outgoing solution of the Maxwell wave equation at a real frequency but with negligible amplitude, heralding the turn-on of a steady-state source of coherent radiation. Time-reversing this threshold lasing equation maps the laser system to another physical realizable electromagnetic system, one in which the time-reflected lasing mode is incident on an identical resonator, except that absorption loss replaces gain. This mapping implies that under very general conditions, any complex structure can be made to absorb perfectly at a specific frequency, if a specific adapted input wavefront is imposed and the loss is appropriately tuned, a phenomenon now known as Coherent Perfect Absorption (CPA). In the following years this effect has been demonstrated in a wide variety of electromagnetic platforms, as well as in acoustic and other wave systems. More recently CPA has been understood to be one limiting case of a completely general theory of reflectionless scattering of linear waves. Just as every scattering structure has a complex spectrum of resonances, when excited at short enough wavelengths, one can show that every such structure has a complex spectrum of Reflectionless Scattering Modes (RSMs), distinct from the resonances, which can be tuned to enable perfect impedance-matching. I will review a few dramatic experimental and technological applications of CPA and RSM. One novel proposal applies these theories to the quantum scattering of atomic condensates to detect bound states in the continuum.

Biography:
A. Douglas Stone is Carl A. Morse Professor of Applied Physics, and Professor of Physics at Yale University, where he joined the faculty in 1986. Since becoming a full professor in 1990, he has served as Chair of Applied Physics (1997-2003, 2009-2015), Director of Yale's Division of Physical Sciences (2004-2009), and Deputy Director of the Yale Quantum Institute (2015-present).

Stone is a theoretical physicist with research interests in condensed matter and optical physics. He was a pioneer in the field of mesoscopic physics, describing systems intermediate between bulk solids and individual atoms or molecules, where his work led to the discovery of “Universal Conductance Fluctuations". Subsequently he worked on problems relating to the effects of chaos in quantum and electromagnetic systems, and was the first to introduce and study lasers with ray-chaotic resonators. His current work continues to focus on lasers, and other photonic systems with complex geometry and gain and loss. He is the author of over 150 research articles and holds five patents for optical devices. He was awarded the 2015 Willis Lamb Medal for Laser Science for his work on random and chaotic lasers (jointly with Hui Cao), and is a co-inventor of the Coherent Perfect Absorber (or “anti-laser), and of the “D-laser", a recently developed speckle-free bright light source for medical imaging and microscopy applications. He is a Fellow of the American Physical Society and of the Optical Society of America, and is an Honorary General Member of the Aspen Center for Physics.

Stone received his undergraduate degree from Harvard in Social Studies in 1976, a Master's degree in Physics and Philosophy from Balliol College, Oxford in 1978 (where he was a Rhodes Scholar) and a PhD in Theoretical Physics from MIT in 1983. He about science for general audiences; his book Einstein and the Quantum (Princeton University Press, 2013) received the Phi Beta Kappa science book award in 2014.



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