Single-Pass Multi-Watt Second-Harmonic-Generation in Congruent and Stoichiometric LiTaO3

We present a comparison of an efficient, single-pass second-harmonic-generation (SHG) of a continuous-wave Yb-fiber laser using a 1) congruently grown LiTaO₃ crystal and 2) stoichiometrically grown LiTaO₃ crystal. Using a Yb-fiber laser pump source delivering a single-frequency output of 40 W at 1064 nm, we have generated ~ 8.5 and 14.5 W of single-frequency green-radiation at 532 nm from 8 mol% MgO-doped periodically poled, congruently grown LiTaO₃ (MgO:cPPLT) crystal and 0.5 mol% MgO-doped periodically poled, stoichiometrically grown LiTaO₃ (MgO:sPPLT) crystal, respectively. We obtained SHG conversion efficiencies in excess of 24% for 5-cm long MgO:cPPLT and ≥36% for 3-cm long MgO:sPPLT. The impact of thermal dephasing was evident in variation of SH power in case of MgO:cPPLT crystal. However, the manifestations due to thermal effect were found out be significantly weaker in case of MgO:sPPLT. This lead to saturation of SHG efficiency at pump powers ≥20 W for MgO:cPPLT. The long-term peak-to-peak power-fluctuation in case of MgO:sPPLT is recorded to be ≈ 4 % for the green beam over a 4-h duration which shows improved performance over MgO:cPPLT output (peak-to-peak power-fluctuation ≈ 11 %). In addition, the 532-nm radiation exhibited single-frequency characteristics with linewidth of 12 MHz (MgO:cPPLT) and 5 MHz (MgO:sPPLT).