Pulsed laser second harmonic generation and thermal dephasing in periodically poled crystals

Computational study of nanosecond pulse laser radiation in periodically poled LiNbO3 and LiTaO3 crystals reveals the complex spacio-temporal evolution of the 1.064 μm fundamental harmonic (FH) and second harmonic (SH) energy fields with associated temperature fields, leading to the thermal dephasing and inhibition of second harmonic generation (SHG). The investigated range of the laser input power is W0=0.5-50 W (with the pulse energy Q0=0.01-1 mJ/pulse and repetition rate of 50 kHz). For input laser powers W0>10 W the FH and SH energy fields are found to strongly couple with non-uniform temperature field leading to significant thermal dephasing and SHG efficiency loss. Heat generation and temperature distributions also exhibit very significant non-uniformities along and across the laser beam, maximizing at the rear or inside the crystal, depending on the input power. Performed study shows the feasibility of the effective thermal control with temperature gradient along the crystal allowing one to maintain (i) the irradiated zone within the temperature tolerance range and (ii) high SHG efficiency under high input laser powers.