DIFFERENCE-FREQUENCY-GENERATION OF 4-MU-M RADIATION FROM ND-YAG LASERS

More than 30 mJ of mid-IR 4-mu m energy was generated with difference-frequency mixing of 1.064- and 1.444-mu m Nd:YAG laser pulses in a lithium niobate crystal. The energy conversion efficiency in converting from the pump at 1.064-mu m to the mid-IR at 4.043 mu m was similar to 5.5%. The amount of 4-mu m 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).