title: Performance of Nd:YAG lasers in coupled generalized self-filtering and positive-branch unstable resonators.
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 approximately 70 mJ, 5.5 times greater than when a single GSFUR design was used. The output beam had a pulse duration of approximately 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.
authors.affiliation: Laser Research Center of the Atomic Energy Organization of Iran, PO. Box 11365-8486, Tehran, Iran.
authors.forename: A H
authors.initials: AH
authors.lastname: Farahbod
authors.forename: B
authors.initials: B
authors.lastname: Daneshvar
authors.forename: A
authors.initials: A
authors.lastname: Hariri