LiNbO_3 Pockels cell for Q-switch of Er:YAG laser

摘要

Generation of a giant pulse of Er:YAG laser is complicated mainly due to the properties of the Er:YAG active medium itself. It is caused by the short lifetime of the Er:YAG crystal upper laser level and a small gain for one pass of the radiation through the active medium. In our case, a specially designed LiNbO_3 electrooptic shutter was used for Q-switching of Er:YAG laser. Brewster angles were employed at the LiNbO_3 crystal faces to avoid the inclusion of a polarizer into the resonator. Even if EnYAG crystal emission is naturally unpolarized we have found that polarization sensitive reflections at two Brewster-cut ends of Pockels cell are sufficient to reach an extinction ratio necessary for giant pulse generation. By help of theoretical analysis based on Jones calculus was found the dependency of Pockels cell radiation transmission on applied voltage. Calculated transmission of Brewster-Brewster LiNbO_3 Pockels cell operating in quarter-wave regime was 30% in closed state. Theoretically and experimentally was found, that for 25 mm long LiNbO_3 crystal, voltage 1.4kV is sufficient for Q-switching. The stable running Q-switched EnYAG laser system was realized with above described Pockels cell. The generated giant pulse length and energy was 70 ns and 26 mJ, respectively.