A resonant optical cavity as a one way light valve

 

Dr. T. Hijmans, WZI-UvA

 

An experiment is performed in which a pulse of laser light is captured inside a high-finesse cavity that is much smaller in size that the spatial extent of the original pulse. Normally a high-finesse cavity can be used to reduce the bandwidth of impinging light, but the the expence of energy: The non-resonant modes are simply rejected. What happens hers seems impossible at first glance: only one cavity resonance overlaps with the spectral content of the pulse and this resonance is much narrower that the original spectral width; yet all the energy present in the pulse is transferred into the single cavity mode. There is no filtering,  entropy is conserved and the transfer is reversible and adiabatic. The trick is the use of a device to couple the light into the cavity that  is equivalant to a mirror with a variable reflectivity.

The principle of the method, and a proof-of-principle experiment are described. We discuss a possible application.

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