Diffraction-limited Nd:glass and alexandrite lasers using graded reflectivity mirror unstable resonators

Abstract

A high reflectivity, graded reflectivity mirror (GRM) design has been recently developed for use in low-gain lasers. A GRM with 63% central reflectivity was used as an output coupler in a low magnification (M equals 1.4) unstable resonator Nd:Glass laser to obtain a Q-switched energy of 2 J in a 25 ns pulse and over 3.7 J in fixed-Q operation. The beam has a diffraction limited divergence of 0.15 mrad. In an Alexandrite laser, a GRM having a central reflectivity of 78% was used in a M equals 1.2 unstable resonator. A fixed-Q output energy of over 500 mJ and a Q-switched energy of 400 mJ was obtained in a diffraction-limited beam. The second harmonic output was increased by a factor of ten from that obtained with a multimode stable resonator.