Broadband mid-infrared generation in elliptically pumped periodically poled lithium niobate devices

Summary form only given. We report the use of highly elliptical pump beams to generate broadband mid-infrared (IR) light in nanosecond-pulsed periodically poled lithium niobate (PPLN) optical parametric generators (OPGs) and monolithic optical parametric oscillators (OPOs). Standard electric field poling techniques were used to fabricate 0.5-mm thick PPLN crystals (a) with a uniform 29.75-/spl mu/m grating period over a 12-mm width and (b) with a fan-out grating structure that varies continuously from 25.5 /spl mu/m to 31.2 /spl mu/m across a 15-mm width. After poling, the crystals were cut and polished to 25-mm and 50-mm lengths. Some crystals were polished with wedged output faces to prevent back reflections from oscillating while the rest were polished with plane parallel endfaces such that the Fresnel reflections would set up a low-finesse, monolithic cavity in the crystals themselves.