Infrared optical parametric fluorescence and parametric oscillation

The properties of optical parametric fluorescence and parametric oscillation are considered in detail. Parametric fluorescence occurs when a pump light source (usually a laser) is incident on a nonlinear crystal; an input pump photon is "split" into two new photons whose energies sum to that of the pump. The frequencies of the fluorescence output can be tuned by varying the nonlinear crystal refractive indices. In a parametric oscillator, an optical resonator is used to provide feedback at the fluorescence frequencies so that coherent oscillations occur. The result is a coherent, narrow bandwidth light source which is wavelength-tunable over thousands of angstroms. For use in theoretical discussions, the nonlinear equations which describe three-wave parametric interactions are derived from Maxwell's equations. The interaction equations are given in a general form which exhibits the spatial and temporal dependence of the fields. The equations are solved for the case of a steady-state, non-depleted pump, parametric amplifier. The power, bandwidth, and angular dependence of parametric fluorescence are theoretically discussed in detail. Experimental measurements using a 1.06μ, Nd:YAG laser are in good agreement with the theory. The experiments constitute the first observation of parametric fluorescence in the infrared. The theoretical properties of parametric oscillators are discussed using a simple but rigorous Fabry-Perot analysis. The analysis gives the threshold and oscillation frequencies of a parametric oscillator and the results are used to provide some insights into an oscillator's bandwidth and stability. The rise time of a pulsed parametric oscillator driven by a Q,-switched pump is analyzed rigorously for the first time. The analysis gives a minimum peak pump power for oscillation which can be substantially larger than the "cw" threshold power. Measurements on a 1.06μ-pumped, internal, LiNb03 parametric oscillator are presented. The threshold, bandwidth, mode spectra, tuning range, and time behavior are discussed and compared to theory. The experimental results show good qualitative agreement with theory except that the bandwidth is nearly an order of magnitude smaller than expected. Peak power conversion efficiencies of 50% are observed along with 10% average power conversion. Several suggestions are made for improving the performance of this type of parametric oscillator.