Abstract

Submicroscopic spider threads are used to support microscopic water droplets (9–60-μ diameter) in backscattering experiments with a 6328-Å laser. Van de Hulst’s analysis of the far-field radiance is modified to a near-field analysis and it is shown that the quantity C₂/C₁, which determines the radiance of the rings of the “glory,” can be obtained from measurements of the polarized components of the backscattered surface wave. For droplets with diameters between 9 and 15 μ, C₂/C₁ is 4.5±1.0, in agreement with Van de Hulst’s deduction from reported observations of the radiance and polarization properties of the rings formed by an artificial mist. The ratio of the radiance of the geometrical-optics contribution to the total backscattered radiance is measured vs droplet diameter; the measurements agree with Nussenzveig’s calculations at a size parameter of 130 (25-μ diameter). The results indicate that for droplets with size parameters larger than 370 (71-μ diameter), the backscattered radiance may be computed on the basis of geometrical-optics considerations alone. When the irradiation is limited to a cone of 2° semiangle, the geometrical-optics contribution is not visible for droplets smaller than 15 μ. For these small droplets, the entire radiance is due to surface-wave radiation.

© 1970 Optical Society of America

Particle-Size Measurement Using Forward-Scatter Holography*

Daniel J. Stigliani, Raj Mittra, and Richard G. Semonin
J. Opt. Soc. Am. 60(8) 1059-1067 (1970)

Optical Back Scattering from Single Water Droplets*

T. S. Fahlen and H. C. Bryant
J. Opt. Soc. Am. 58(3) 304-310 (1968)

Laser backscattering from dense water-droplet clouds

J. S. Ryan, S. R. Pal, and A. I. Carswell
J. Opt. Soc. Am. 69(1) 60-67 (1979)

Complex angular momentum theory of the rainbow and the glory

H. M. Nussenzveig
J. Opt. Soc. Am. 69(8) 1068-1079 (1979)

How are glories formed?

Philip Laven
Appl. Opt. 44(27) 5675-5683 (2005)