Abstract

The density of morphology dependent resonances (MDRs) of microspheres is much larger than the density observed in typical resonance spectra. It is large enough to be consistent with observations¹ of multiorder Stokes emission in the stimulated Raman scattering from microspheres. The question of whether MDRs having extremely large cavity Q (> 10¹⁰ if the spheres are lossless) contribute to the optical feedback in real spheres is discussed. Only the low-order very narrow linewidth MDRs have angle-averaged intensities that are consistent with photographs² of the light emission from lasing spheres. Although the integrated area under the scattered field coefficients tends to zero as the cavity Q increases, the area under the internal field coefficients (which are proportional to the intensities of stimulated processes) gradually increases as the cavity Q increases. Hence it would appear that the very high Q MDRs provide the optical feedback for stimulated processes in microspheres. When a sphere is illuminated with a high intensity laser beam a nonuniform refractive index may be induced which may so perturb or couple the low-order MDRs that it may not be appropriate to ascribe the optical feedback to the MDRs of homogeneous spheres.

© 1986 Optical Society of America