Temperature-controlled picosecond-pulsed high frequency second-harmonic generation by a periodically poled...

We report experimental results of second-harmonic (SH) generation (SHG) by a quasi-phase-matched periodically poled Mg-doped stoichiometric LiTaO(3) 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/cm(2) and under repetition rate 10-20 kHz. For I>3 GW/cm(2) SHG efficiency achieves the saturation level of η≈0.35 which can be maintained within a wide range of I = 3-9.5 GW/cm(2). The loss of SHG efficiency observed for I>5 GW/cm(2) 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 V(2) 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 ≈I(2) (-1)dI2/dz≈-(0.8-8) cm(-1) for I = 1-9.5 GW/cm(2).