SECOND HARMONIC GENERATION IN PERIODICALLY POLED NONLINEAR CRYSTALS WITH 1064 nm GAUSSIAN LASER PULSES

Fundamental output beam of 1064 nm wavelength emitted by a diode-pumped and passively Q-switched Nd:YAG microchip laser was frequency doubled in an 8 mm long periodically poled potassium titanyl phosphate (PPKTP) crystal. More than 12 μJ green pulse energy was obtained for 20 μJ fundamental pulse energy, corresponding to 60% second harmonic (SH) conversion efficiency. The power density of the fundamental pulse focused inside the nonlinear crystal was about 25 MW/ cm 2. In order to maximize SH conversion efficiency, the operating temperature of the nonlinear crystal was controlled by using a thermoelectric cooler. The thermal acceptance of the PPKTP crystal was experimentally determined, resulting a fullwidth-half-maxim (FHWM) value of 5.7°C. The nonlinear coefficient of the PPKTP was estimated at 6.9 pm/V. The present paper describes a laboratory work elaborated for master students of the Faculty of Physics from University of Bucharest.