Compact 12mJ mid-IR pulsed source using an intracavity KTA OPO followed by a CSP OPA

We describe a compact mid-IR source utilizing an intracavity, non-critically phase matched potassium titanyle arsenate (KTA) optical parametric oscillator (OPO) placed inside a passively Q-switched (PQS), 1.06μm Nd:YAG laser resonator. The 20mm long KTA intracavity OPO was singly resonant, with the output coupler coated for partial reflectivity of 60% at the 1.5μm signal emission and for high transmission at the 3.5μm idler wavelength. With the Nd:YAG pumped by a 3-λ 12-bar diode stack at 5Hz PRF, the OPO generated a maximum 20mJ signal pulse at 1.5μm and 8.8mJ idler pulse at 3.5μm. A cadmium silicon phosphide optical parametric amplifier (OPA), phase matched for 1.5μm-pumped amplification of the 3.5μm OPO idler, was placed in the near field of the intracavity OPO to further increase the mid-IR pulse energy. A maximum 3.5μm pulse energy of 12.1mJ was measured after the OPA, with an additional 4.0mJ measured at 2.8μm. The 3.5μm pulses had a temporal duration of 20ns, corresponding to a peak-power of 605kW. This paper will detail the Nd:YAG pumped intracavity KTA OPO/CSP OPA and optimization of its performance for maximizing the mid-IR pulse energy.