Summary Some optical polarization effects for very fine powders are shown. The well-known curve of polarization versus phase angle is found to change in shape and scale when the grain size is reduced to less than the wavelength; strong negative polarization is found, even for a smooth powder surface of high albedo. The negative peak changes in shape, and its parameters are found to be related to grain size in simple ways. This distinctive shape provides a possible remote-sensing method for detecting subwavelength grains on planetary surfaces.

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