반도체 포화 흡수체 거울을 이용한 Yb:YAG 레이저의 Q-스위칭 및 모드 잠금에 관한 연구

Abstract

By longitudinally pumping a Yb:YAG laser with a laser diode, a high output power and good quality beam profile can be obtained. If this Yb:YAG laser can be operated as a pulse laser, then the laser can be utilized in a range of fields requiring high-precision materials processing. One pulse generation method is the installation of a saturable absorber inside the laser cavity, such as the semiconductor saturable absorber mirror (SESAM) used with solid state lasers. Depending on the conditions of the SESAM and cavity, the laser can be operated in Q-switched, mode-locked, or Q-switched and mode-locked pulse modes. The easiest way to select the pulse mode is to adjust the cavity length; when the cavity length is elongated, the laser changes from the Q-switching to the mode-locking mode with the help of the SESAM. In this thesis, we study Q-switching and mode-locking of an Yb:YAG laser using an SESAM. To optimize the pumping optics of the laser cavity, we investigated the dependence of the laser output on the radius of curvature of the dichroic mirror used for the longitudinal pumping. The designed continuous wave (CW) laser has a slope efficiency of 26.3% and a beam quality (M2) of 1.13. The SESAM and a short cavity with the designed pumping optics generate Q-switched pulses from the Yb:YAG laser with a pulse width of about 220 nm and a maximum energy of 20.5 mJ. Furthermore, the SESAM and a longcavity produced a mode-locked pulse with a pulse width of about 880 ps and an average power of 460 mW at a 20 MHz repetition rate.