Room temperature high power frequency conversion in periodically poled quasi-phase-matched crystals

Near-stoichiometric lithium tantalate (SLT) crystals were produced from congruent lithium tantalate by a vapor-transport equilibration (VTE) process. The VTE'ed SLT (VSLT) crystals exhibited very low coercive field of 60-120-V/mm and improved high intensity damage resistance. The ~603°C Curie temperature of the congruent raw material climbed to 693±0.1°C in the VSLT crystal regardless of the congruent crystal stoichiometric composition or of the exact VTE process temperature profile. Stable, high power near room temperature second harmonic generation (SHG) and optical parametric oscillation (OPO) were demonstrated with these crystals. SHG measurements of a 1064-nm pulsed laser were realized by an 8-μm period grating, 21-mm-long sample. With 29-ns long pulses at 20-kHz repetition rate, 7.3-W (average power), of 532-nm radiation was generated with 55% conversion efficiency. With 25-ns long pulses at 10-kHz repetition rate in the same sample, 6.3-W of average-power with 61% conversion efficiency was obtained. 1.41-W average-power, at 4.013-μm idler wavelength was generated in an OPO configuration. The 28.65-μm period grating, 24-mm-long sample, was pumped by 25-ns pulses, 10-kHz repetition rate, 1.064-μm Nd:YVO 4 laser. In addition to the original (intended) signal and idler wavelengths, 0.27-W was obtained at 4.686-μm idler wavelength, by a secondary OPO process which developed in the system. Primary and secondary OPO operation was also observed in a 27.15-μm period grating, 38-mm-long sample. 0.67-W at 4.48-μm and 0.15-W at 5.03-μm were generated in this experiment.