Abstract

Second-harmonic (frequency-doubling) nonlinear mirrors proposed originally for passive mode-locking^1,2 are versatile optical devices that can perform a large number of functions in controlling the laser operation. The devices are very simple: a combination of one or two frequency-doubling crystals and a dichroic mirror. The principle of operation is based on conversion of the laser radiation into second harmonic in the frequency-doubling crystal, followed by conversion back into fundamental, or further conversion into second harmonic in the same or a second crystal. The direction of the energy flow between the fundamental and the second harmonic in the second interaction is governed by the phase relationship between the interacting waves. As a result, the nonlinear reflectivity R_ml of the crystal-mirror combination is increasing (dR_ml/dl>0), or decreasing (dR_ml/dl<0) with respect to the light intensity 1.

© 1992 Optical Society of America