Improved Monoblock laser brightness using external reflector

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  mm×3  mm cross section is relatively large (10-12 mrad), it can be reduced to <1  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  mrad, corresponding to a >2.5× reduction from the unmodified laser. Performance using this technique with various feedback and etalon spacings is presented.