EFFICIENT, TUNABLE OPTICAL EMISSION FROM LiNbO3 WITHOUT A RESONATOR

Abstract

We report the first observation of tunable stimulated optical emission from a nonlinear crystal without the use of an external resonator, and with greater than 50% conversion of the pump beam to the tunable frequency. Opposite faces of a LiNbO₃ crystal were polished flat and parallel to provide for multiple reflections of the signal radiation (Stokes) inside the crystal. The A₁ symmetry 248‐cm⁻¹ polariton mode was excited with a Q‐switched ruby laser, and the signal frequency was tuned by varying the angle of incidence of the laser beam relative to the normal to the crystal surface. Operation was at room temperature; no crystal damage was observed over most of the tuning range; and laser depletion occurred within the first few nanoseconds of the Q‐switched pulse. The difference between the Stokes frequency and laser frequency was varied from 42 to 200 cm⁻¹, and the corresponding idler wavelength was varied from 238 to 50 μ.