레이저 다이오드로 종 펌핑된 디스크형 Yb:YAG 레이저 출력 특성

Abstract

With the advent of laser diode pumping technology, high power, high beam quality, and compact lasers could be realized. However, laser engineers are still interested in developing more compact lasers with higher power and higher beam quality. One of the excellent candidates for new lasers is the Yb:YAG disk laser longitudinally pumped by a laser diode. Since Yb:YAG crystal has the quantum efficiency of 91% and the life time of 951 μs, the longitudinally pumped Yb:YAG lasers can be operated with high output power and high quality beam profile. The CW Yb:YAG disk laser with more than 100 W in TEM00 mode[1]. An electro-optical efficiency of 20% and an optical conversion efficiency of 58% had been achieved and a laser power of 1 kW had been demonstrated. In this thesis, we demonstrate a Yb:YAG disk Laser longitudinally pumped by laser diode with the wavelength of 940 nm and investigate its output characteristics. To design a high efficient laser, we optimized the lens system to tightly focus the pump beam on the Yb:YAG disk. Also we fabricated the laser crystal mount cooled by a water circulation. We used the plane-parallel resonator consisting of a Yb:YAG disk (φ 5 mm x 3.5 mm) with Yb-doping rate of 5% and a output coupler of 97% reflectance. Maximum output power of the designed laser was 4.36 W at the 23.5 W pump power and its slope efficiency was 22%. We also investigate the beam quality(M2) of the output beam. The measured beam quality (M2) depended on the resonator length and the pump power. The designed laser had M2 value of 1.3 under best experimental conditions, which means almost Gaussian beam.