We present a two-stage system for parametric frequency conversion of high-energy Nd:YAG laser pulses to the 3-5 μm range. The first stage, which converts from 1.06 μm to about 2.1 μm, is based on KTiOPO4 (KTP) and has a master oscillator / power amplifier (MOPA) architecture, where the oscillator is an optical parametric oscillator (OPO) and the amplifier is an optical parametric amplifier (OPA). This architecture ensures that the 2.1 μm beam quality is good enough for pumping a ZnGeP2 (ZGP)-based OPO in the second stage. With 500 mJ from the Nd:YAG laser we obtain up to 138 mJ signal and 80 mJ idler in orthogonal polarizations at 2.1 μm. Using 86 mJ of the signal to pump the ZGP-OPO we have so far obtained 28 mJ in the 3-5 μm range.

© 2005 Optical Society of America

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