Abstract

The Monoblock laser has become the laser of choice in long-range, eye-safe laser range finders. It is eye-safe with emission at 1570 nm, high pulse energy, simple construction, and high efficiency when pumped by a laser-diode stack. Although the output beam divergence of a typical Monoblock with a $3\mathrm{mm}\times 3\mathrm{mm}$ cross section is relatively large (10–12 mrad), it can be reduced to $<1\mathrm{mrad}$ using a telescope with large magnification. In this paper we present a simple and compact technique for achieving significant reduction in the Monoblock beam divergence using a partial reflector that is placed a short distance from the optical parametric oscillator (OPO). Using a 38 mm long Monoblock with a 10 mm long potassium titanyl phosphate OPO, we achieved a beam divergence of $<4\mathrm{mrad}$, corresponding to a $>2.5\times$ reduction from the unmodified laser. Performance using this technique with various feedback and etalon spacings is presented.

© 2014 Optical Society of America

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