SPONTANEOUS EMISSION AND OSCILLATION IN A PLANAR MICROCAVITY DYE-LASER

Characteristics of a planar microcavity laser using rhodamine 6G with pulsed excitation is studied. Theoretical aspects of controlled sponta neous emission and oscillation in a planar microcavity laser are discu ssed. The measured spectrum and the angular divergence of spontaneous emission below threshold are in good agreement with theory. The angula r divergence yields the radius of the cavity quasimode. The spontaneou s emission coupling ratio obtained from the measured input-output char acteristics is in reasonable agreement with the theoretical value. The expression for the coupling ratio derived for a Fabry-Perot-type micr ocavity is shown to be essentially equal to that of a closed cavity or guided mode cavity derived by Yamamoto, Machida, and Bjork [Phys. Rev . A 44, 657 (1991)]. The observed spectral behavior near the threshold approximately follows the Schawlow-Townes formula, but for a limited range of output power. The observed spectrum and divergence above thre shold indicate incoherence much worse than the Schawlow-Townes limit.