Patent ID: 8613520

Claim:
An optical cavity device, comprising: a first mirror element having an internal surface and an exterior surface, wherein a first portion of the internal surface comprises a reflective coating defining a reflective surface, and wherein a second portion of the internal surface comprises an anti-reflective coating defining an optically transmissive window portion of the internal surface, wherein the window portion is solid; and a second mirror element having an internal surface and an exterior surface; and a housing structure configured to hold the first and second mirror elements such that the internal surfaces of the first and second mirror elements are facing each other along a common axis and defining a cavity therebetween, wherein a radiation beam that enters the cavity through the optically transmissive window portion of the first mirror element and impinges on the internal surface of the second mirror element repeatedly reflects off of the internal surfaces of the first and second mirror elements multiple times before exiting the cavity through the optically transmissive window portion.