Theory of Parametric Oscillator Threshold with Single-Mode Optical Masers and Observation of Amplification in LiNbO3

Theoretical and experimental results are given on cw parametric amplification and oscillation. Theoretical calculations incorporating Gaussian-mode theory into parametric-amplifier theory indicate that continuous parametric oscillation in LiNb${\mathrm{O}}_3$ using a gas-laser pump source should be achievable with tens of milliwatts of pump power. The requirements for achieving simultaneous resonance of signal and idler frequencies under phase-matched conditions for parametric oscillators are discussed. The effects of varying crystal temperature, electric field, and pump frequency to satisfy these requirements are included. The experiments involved the measurement of difference-frequency power at 0.9299 μ (10 754 ${\mathrm{cm}}^{-1\mathrm{}}$) produced in LiNb${\mathrm{O}}_3$ by mixing a signal at 1.1526 μ (8676 ${\mathrm{cm}}^{-1\mathrm{}}$) from the He-Ne laser with a pump at 0.5147 μ (19 430 ${\mathrm{cm}}^{-1\mathrm{}}$) from an argon ion laser. The LiNb${\mathrm{O}}_3$ crystal was adjusted in temperature so as to obtain phase matching normal to its optic axis, thus avoiding the deleterious effects of double refraction. The observed amplification was found to be in agreement with theory. Experimental results are given demonstrating low-loss resonators for the signal and idler frequencies, the loss being approximately 1% per pass. Data showing the dependence of optical path length in an optical resonator on temperature and electric field are given. The variation of the phase-matching condition with electric field is demonstrated in a second-harmonic-generation experiment.