Thermo-Optic Effects in Congruent-LiTaO3 Based Continuous-Wave Optical Parametric Oscillator

We present an experimental study on single-frequency, singly-resonant optical parametric oscillator (SRO) comprised of 50 mm long congruently-grown, 8-mol%-doped, periodically-poled LiTaO
₃
(MgO:cPPLT) crystal. The SRO is pumped by a single-frequency, fiber laser pumped green laser. Our observations reveal that the SRO output (idler) scales linearly with the pump power ( P
_p
) near the SRO threshold ( P
_p(th)
). However, the SRO idler power ( P
_i
) exhibits strong saturation at pump power ≈ 1.5P
_p(th)
which eventually switches-off the SRO operation on further pump-power enhancement. By coarsely tuning the MgO:cPPLT crystal temperature from 50
^o
C to 170
^o
C, the SRO idler wavelength is varied from 1810-1920 nm wavelength band. A maximum idler power P
_i
=583 mW was obtained when the input pump power was ≈ 3.1 W. The idler power saturation is accompanied by discernible distortion in idler beam profile. An early onset of saturation in MgO:cPPLT is essentially a consequence of strong linear absorption exhibited by MgO:cPPLT at pump wavelength, its high thermo-optic coefficient as well as low thermal conductivity. The results are theoretically analyzed by solving the heat conduction equation which provides a deeper insight about the impact of pump-induced thermo-optic effects on a three-wave interaction process.