A Means Of Eliminating The Effects Of Particulate Contamination On Scatter Measurements Of Superfine Optical Surfaces

Carl S. Masser

doi:10.1117/12.962862

2 January 1990 A Means Of Eliminating The Effects Of Particulate Contamination On Scatter Measurements Of Superfine Optical Surfaces

Carl S. Masser

Author Affiliations +

Proceedings Volume 1165, Scatter from Optical Components; (1990) https://doi.org/10.1117/12.962862
Event: 33rd Annual Technical Symposium, 1989, San Diego, United States

Abstract

Mirror scatter is a very important parameter for ring laser gyroscopes. For this reason, the Northrop Research and Technology Center has built an automated scatterometer capable of performing raster scans as a means of producing spatially resolved scatter information. The apparatus is flexible, with a minimum spot size of 5 microns and a maximum data rate of 1.5 Hz. Particulate contamination has proved to be a very serious problem with these measurements. An attempt to clean the part will result in no fewer of these particles; they are merely moved to different locations. Thus the particulate contribution to scatter can often be greater than that from the "real" features. A means has been devised to take advantage of the fact that, though the particulate contamination can never be completely eliminated, specific particles will tend to move around when the part is cleaned. In order to implement this technique, a means is needed whereby the part can be removed from the scatterometer and cleaned. After cleaning, the part must be replaced in exactly the same position within the scatterometer as before. Comparison of two scatter plots, one made before the part was cleaned and one after, will reveal which scatter features are due to particulate contamination and which are not: those features that appear in both plots are taken as real features. Presented will be a discussion of the equipment needed to implement the technique described. Also presented will be a comparison algorithm which can be expected to yield statistically meaningful data even for a large number of data sets. Actual scatter plots demonstrating the effectiveness of the technique will also be presented.

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Carl S. Masser "A Means Of Eliminating The Effects Of Particulate Contamination On Scatter Measurements Of Superfine Optical Surfaces", Proc. SPIE 1165, Scatter from Optical Components, (2 January 1990); https://doi.org/10.1117/12.962862

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KEYWORDS

Optical components

Contamination

Mirrors

Particles

Scatter measurement

Sensors

Silicon

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