Optical properties of cometary dust

The application of measured optical constants to the interaction of electromagnetic radiation with small cometary dust particles is discussed, with emphasis on the interpretation of cometary observations. It is found that in some spectral regions optical constants vary greatly with wavelength. The optical constants may be incorrect. Because of errors in measurement, or the application of the Kramers-Kronig relationship over too small a spectral region, or an improperly prepared sample, the derived optical constants may be in error. It is suggested that a full Kramers-Kronig analysis and application of the more important sum rules should be performed on any set of optical constants whose accuracy is important. Optical constants derived from the measurement of inhomogeneous materials, where the inhomogeneities are of comparable size to that of the beam of radiation used in the experiment, should not be used to predict the optical properties of small particles.