For thermal emission from particles the conventional size parameter X = 2πa/λ does not distinguish between small and large particles. We show that the opacity parameter Ω = 4πka/λ = 2kX is a more accurate means of demarcating the two emission regimes. Ω is approximately equal to the particle’s mean optical depth, and it can be derived from both scattering theory and geometrical optics.
© 1999 Optical Society of America
Original Manuscript: March 2, 1999
Revised Manuscript: May 21, 1999
Published: August 20, 1999
David K. Lynch and Stephan Mazuk, "Size parameter for thermally emitting particles," Appl. Opt. 38, 5229-5231 (1999)