A coherent infrared source tunable from 3.4 to 5.3 μm has been constructed by difference-frequency mixing of the second harmonic of a Q-switched Nd:YAG laser and a pulsed dye laser using the new crystal KTiOAsO<sub>4</sub> (KTA). A peak power of >50 kW and pulse energy of >250 μJ are measured at 4.4 μm. The results are compared with mixing in LiIO<sub>3</sub>. For a low-power Nd:YAG laser that produces 200 mJ of 532-nm radiation, the infrared power is similar for the two crystals. For high-power YAG lasers, calculation shows that commercial KTA crystals can produce over 10 mJ of IR power in the absence of absorption loss. The laser damage threshold of KTA at 532 nm is determined to be 300 ± 30 MW/cm<sup>2</sup>. Both the maximum IR power and the damage threshold are several times higher for KTA than for LiIO<sub>3</sub>. A simple frequency calibration method is described.

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