Reflectivity of Single Micron Size Irregularly Shaped Dust Grains

Abstract

We have developed a microscopic technique to measure the optical albedo of single, micron size (5 to 7 μm in diameter) irregularly shaped dust grains in the wavelength range of λ ~ .35 μm to 0.6 μm. The experimental setup consists of a microscope, photometer, polarization analyzer and light sources. The illuminating spot size is limited to 5 μm in diameter. Dust grains are mounted on the tip of a thin (1 μm) glass fiber in order to reduce the background illumination. Our results on single, micron size carbonaceous chrondite type meteorites with application to the optical properties of interplanetary dust grains and stratospheric particles are presented. Our results indicate that single grains of carbonaceous chrondite material have an optical albedo of 5% at λ ~ .35 μm which decreases to 2% at λ ~ 0.55 μm. Scattered light from single grains is strongly polarized and it also exhibits an angular dependence.