Thermally stable third harmonic generation using type 1 LBO

Summary form only given. The third-harmonic light sources of Nd:YAG/YLF lasers have begun to be utilized for drilling via holes in print circuit boards according to the progress of high-density fabrication. Fast rise-time in burst mode operation and high pulse energy stability are required for the light source in this industrial use. Because of simple construction and less optical component requirement, type I SHG-type 2 THG(LBO) scheme has often been used for the third-harmonic generation. However it has unstable rise-time property in high average power operation. In the experiment the THG output was >5.6 W, and the phase-matching angle was tuned at the THG crystal temperature 50/spl deg/C and fixed constant through out the experiment. The upper waveforms show fundamental inputs operated at 5-kHz repetition frequency and the lower ones show the THG outputs at 49, 50, and 51/spl deg/C of the THG crystal temperature, respectively. As shown only +/- degree temperature offset causes elongated rise-time in THG output. The THG power absorption and accompanying self heating inside the THG crystal are considered to cause these disadvantages. The thermally induced phase mismatch is regarded to be comparable to the temperature bandwidth of the type 2 THG LBO crystal.