Narrow-bandwidth unstable laser resonator

Abstract

A narrow-bandwidth, unstable laser resonator comprising: an output section ncluding a laser gain medium for generating and amplifying light, a first reflective element for reflecting and collimating light from the gain medium back through the gain medium, and a second reflective element having a hole therein, the second reflective element being responsive to the collimated light passed through the gain medium for reflecting most of the collimated light out of the unstable laser resonator as an output beam and for passing the remaining portion of the collimated light through the hole therein as a residual beam; and a feedback ring including an optical path, a beam splitter for passing a first portion of the residual beam into the optical path in a first direction, a frequency-narrowing element disposed at a position in the optical path where the first portion of the residual beam is collimated, the frequency-narrowing element being operative to narrow the frequency bandwidth of the first portion of the residual beam to produce a narrow-bandwidth collimated beam, a lens disposed in the optical path for focusing the narrow-bandwidth collimated beam to cause light from that beam to be reflected from the beam splitter and passed through the hole in the second reflective element as a narrow-bandwidth convergent beam before the narrow-bandwidth convergent beam before the narrow-bandwidth convergent beam is amplified by the gain medium.