Clamping down on causality by probing laser cavities

Since the realization of the first laser cavity countless questions have been asked for which laser light has provided the answer. Numerous questions have also been posed in an effort to improve on our abilities to produce lasers with various performance specifications and wavelengths. A question that was not asked until recently is – what happens if you shine a laser beam through another laser cavity? It may not seem a practical question to ask experimentally, but after studying how externally incident light interacts with an active laser cavity in quantitative detail, the answer turns out to offer devices with new, seemingly paradoxical optical capabilities.