Abstract

We report experimental and theoretical results of temperature-controlled 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 KHz. An optical system including a femtosecond oscillator, stretcher, regenerative amplifier and a compressor with diffraction grating allows the generation of 18 ps pulses of fundamental wavelength with λ₁=1.03 μm with a spectral bandwidth of Δν≈300 GHz and pulse repetition rate νp=10 - 100 kHz. Fig. 1(a) shows SHG efficiency measured for beam radius 0.15 mm. First, SHG efficiency is measured for the quasi-phase-matching (QPM) temperature maintained during the operation (T=T_QPM=40 ^oC) , and, second, for a series of the temperature-controlled SHG operations when the temperature of the metal pedestal was maintained below that of QPM, i.e. at T= 30,32,34 36 and 38 ⁰C. In particular, SHG efficiency measured for T=T_QPM=40 ⁰C shows the saturation η≈0.35 at I=4-5 GW/cm² followed by a monotonous decrease towards η≈0.23 at I=9.5 GW/cm². Our experimental data for the maximum of I=9.5 GW/cm² show that the loss of η in operation at T=T_QPM=40 ⁰C can be completely recovered by decreasing the operational temperature on ΔT≈10 ⁰C.

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