<title>Features of the angle-tuned phase-matched OPO with pump beam reflected</title>

Abstract

The development of compact high efficiency optical parametric oscillators (OPO) which generate widely tunable coherent radiation with small divergence and high angular pointing stability is a currently a topical problem. In the past, many efforts have been made to reduce the spectral bandwidth and the divergence of the OPO output beam. The spatial and spectral properties of a 355nm pumped pulsed ns-BBO OPO were improved by using type II phase matching and pump beam back reflection. In this way the OPO bandwidth was reduced by more than a factor of 20 to less than 0.1nm, and the divergence of the OPO beam was reduced in the phase matching plane by a factor of 5 to 1mrad. We investigated the spectral properties of the type II BBO OPO and KTP OPO pumped at 532nm and pump beam reflected. It was found, that the OPO bandwidth was reduced by more than a factor of 5 to less than 0.3nm at 680nm and 0.7nm at 1064nm. We determined, that in collinear OPO with inclined nonlinear crystal in the forward direction the output signal beam deviates from the pump beam. After reflection at the OPO out-coupling mirror the signal and pump beams inside crystal are non-collinear. After passing through the crystal in backward direction and reflection at the OPO rear mirror the signal and pump beams inside crystal are again collinear.