Selection of longitudinal laser modes by a nontilted intracavity Fabry — Perot etalon

The use of a Fabry — Perot etalon in selection of longitudinal cavity modes was investigated. It was found that a Fabry — Perot etalon may be used for such selection in cavities with a convex mirror without tilting the etalon relative to the cavity axis. This avoids a number of limitations associated with tilting of the etalon. The mechanism of discrimination between the modes and of residual losses introduced by the etalon was analysed theoretically. Mode selection by a nontilted Fabry — Perot was achieved for an argon laser, the cavity parameters were optimised, and a high efficiency of conversion to a single-frequency regime (more than 70% in terms of the multimode lasing power, which was a factor ~ 1.5 higher than for a tilted etalon) was attained.