Temperature-controlled picosecond-pulsed high frequency second-harmonic generation by a periodically poled stoichiometric LiTaO 3

We report experimental results of second-harmonic (SH) generation (SHG) by a quasi-phase-matched periodically poled Mg-doped stoichiometric LiTaO3 crystal for 1030 nm input radiation of 18 ps pulse duration, within the range of peak input laser intensity I = 0.1-9.5 GW/cm2 and under repetition rate 10-20 kHz. For I>3 GW/cm2 SHG efficiency achieves the saturation level of η≈0.35 which can be maintained within a wide range of I = 3-9.5 GW/cm2. The loss of SHG efficiency observed for I>5 GW/cm2 can be recovered to the level of η≈0.35 by using temperature-controlled operation. By applying our experimental data we find the value of two-photon absorption (TPA) coefficient for 515 nm radiation, β≈1.1-2.7 cm/GW, agreeing well with the theoretical estimate β≈2.6 cm/GW. Our analysis suggests that the inhibition of SHG efficiency, its saturation and stabilization are due to a combined mechanism including: (i) non-steady-state ps effect scaled by ≈ζ−2[1-exp(-ζ)]2 as compared with the efficiency for ns pulsed operation (ζ = L/V2τP , L is the crystal length, τP is the pulse duration and V2 is the group velocity of SH); (ii) dephasing caused by the spectral bandwidth of the input radiation (≈300 GHz); (iii) thermal dephasing caused by TPA of SH; and (iv) strong SH attenuation by TPA of order ≈I2−1dI2/dz≈-(0.8-8) cm−1 for I = 1-9.5 GW/cm2.