Abstract

Transparent droplets 5-100 µm in diameter act as natural optical micro cavities. Surface tension shapes the droplets into nearly perfect, spheres, and feedback, required for coherent nonlinear optical processes such as stimulated Raman scattering¹ (SRS), is provided by lightwaves that totally internally reflect at the droplet-air interface and fold back on themselves. Resonances can occur when the circumference of the droplet approximately equals an integral number of wavelengths. Cavity (Qs as high as 10⁸ have been inferred from efficiency² measurements. On resonance, the gains for stimulated and spontaneous processes are expected to be enhanced over bulk liquid values because of the higher density of photon states per frequency and volume. This phenomenon is often called cavity QED or Purcell enhancement³ Modification of fluorescence rates⁴and enhanced lasing gains-in droplets due to this effect have recently been reported.

© 1993 Optical Society of America