Difference-frequency generation of 4-microm radiation from Nd:YAG lasers

More than 30 mJ of mid-IR 4-microm energy was generated with difference-frequency mixing of 1.064- and 1.444-microm Nd:YAG laser pulses in a lithium niobate crystal. The energy conversion efficiency in converting from the pump at 1.064-micro to the mid-IR at 4.043-micro was ~5.5%. The amount of 4-micro output produced was limited by optical damage to the lithium niobate crystal. In this experiment, the optical damage threshold occurred at a peak intensity of 300 MW/cm(2).