Abstract

We report the optimization of optical parametric oscillator (OPO) based on a multigrating periodically poled LiNbO₃ (PPLN) crystal pumped by a Q-switched laser. The PPLN sample was fabricated by electric-field poling in a 0.5-mm-thick, 26-mm-long wafer. The crystal was mounted in an oven held at an elevated temperature of 105°C to minimize photorefractive distortion. The diode-pumped Nd:YAG laser pumped the OPO at 1064 nm with 13-ns-FWHM pulses. The OPO was singly resonant with the signal wave resonated, and the pump beam was optimally matched to the 140-µm signal waist. The input mirror of the 40-mm-long linear cavity had a 60-mm radius of curvature, reflectivities R>99% at the signal wavelength and R<15% at the idler wavelength, and transmission T>97% for pump wavelength. The optimization was performed by using flat output mirrors with different reflectivities at the signal wavelength (see Figure). Double passing the pump with an output coupler reflective at the pump wavelength lowered threshold but did not improve efficiency. Translating the crystal across the cavity allowed pump-beam interaction with the different grating regions (periods from 25.5 to 31.5 µm in 0.25-µm steps) and provided wavelength

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