Abstract
A new optical resonator based on the combination of a generalized self-filtering unstable resonator (GSFUR) and a positive-branch unstable resonator (PBUR) in a three-mirror scheme is reported. It is shown both theoretically and experimentally that a nearly diffraction-limited Gaussian-output laser beam with a large mode volume can be obtained with this cavity design. The laser cavity is particularly interesting for use in high-threshold pumped gain media and eliminates some disadvantages of the SFUR and GSFUR designs. This resonator, with an effective magnification of -6.16, was applied to a pulsed Nd:YAG laser in free-running and in Q-switched modes of operation. The output energy was ∼70 mJ, 5.5 times greater than when a single GSFUR design was used. The output beam had a pulse duration of ∼30 ns in the Q-switched mode of operation and a beam divergence of 0.26 mrad. The required relations for the GSFUR–PBUR optical design and the output energy were derived and verified experimentally.
© 1999 Optical Society of America
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