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This paper describes a method of illuminating the region at and near the surface of a transparent sample or of a film on a transparent substrate. The features then observed, using ordinary microscopic magnification, are a speckle pattern due to surface roughness and discrete points of light due to localized point scattering sites both on and just within the surface. While the technique is similar to dark-field microscopy, here the region just within the surface is highly illuminated, and additional information concerning the size and position of scattering sites can be learned. In this technique the surface is illuminated from within the sample with a well-collimated polarized laser beam at an angle of incidence equal to or greater than the critical angle. When using an s-polarized beam, a standing wave pattern is set up just within the surface of the sample. Since the incident beam is totally reflected, the antinodes have four times the incident beam intensity and the nodes have zero intensity. This standing wave pattern may be translated and the nodal spacing may be changed by changing the angle of incidence and/or changing the laser wave-length. This allows selective illumination of various surface features. Additionally, by the use of a film of matching fluid on the surface under inspection, the roughness-caused speckle pattern may be eliminated leaving only the light coming from point scattering sites. We will describe methods of using this technique to determine certain size and positional features of the discrete scattering sites. Examples of various surfaces as viewed by this technique and other standard techniques are compared. This inspection technique has been used to study surface cleaning methods, laser damage nucleation sites, and ion milling of optical surfaces.
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