Abstract

Sub-nanosecond coherent sources in the mid-IR spectral region (2.5-4 microns) with high average power and high pulse energy are of fundamental interest for both scientific and industrial applications, e.g. remote sensing, molecular spectroscopy and broad medical applications taking advantage of the high water absorption around 3 µm [1]. Optical parametric oscillators (OPO) based on periodically poled quasi phase-matched (QPM) nonlinear materials are especially promising sources due to the exceptionally large nonlinearity and the complete absence of spatial walk-off. Typical nonlinear material for a QPM based OPO in the mid-IR is periodically poled lithium niobate (PPLN). However, its low photorefractive damage threshold together with its high coercive field (21 kV/mm), largely limits its use in high power OPOs [2]. On the other hand, periodically poled KTiOPO₄ (PPKTP) and periodically poled stoichiometric LiTaO₃ (PPSLT) have much lower coercive field (2 kV/mm and 1.7 kV/mm respectively) and higher photorefractive damage threshold. Thus, larger aperture crystals and higher pump energies can be employed. Additionally, PPSLT is transparent up to 4 µm presenting an attractive opportunity to produce high power OPOs at high repetition rates, when used with high power sub-nanosecond laser sources.

© 2011 Optical Society of America