Spectral line narrowing of a degenerate PPLN OPO

Abstract

Laser beams with high peak power and narrow line output are fundamental for non-linear conversion. Novel intracavity techniques which improve the spectral brightness of a high average power, degenerate, periodically-poled Lithium Niobate (PPLN) optical parametric oscillator (OPO) are reported. The OPO was pumped with a modulated, high repetition rate Q-switched Nd:YAG laser, which produced an average power of 20 W in a near-diffraction limited beam. The broadband full width half maximum (FWHM) of the OPO was measured to be 120 nm, with an average power output of 7.7 W. Using an air-spaced etalon in combination with a quartz birefringent filter as line-narrowing elements, this decreased to a line-narrowed average power of 4.5 W, with a full width half maximum (FWHM) of 3 nm. Experimental results indicate that the power loss from the OPO is proportional to the residual loss of the line-narrowing elements in the OPO cavity.