Performance evaluation of 2-D adaptive prediction filters for detection of small objects in image data.

This work studies the performance of dimensional least mean square (TDLMS) adaptive filters as prewhitening filters for the detection of small objects in image data. The object of interest is assumed to have a very small spatial spread and is obscured by correlated clutter of much larger spatial extent. The correlated clutter is predicted and subtracted from the input signal, leaving components of the spatially small signal in the residual output. The receiver operating characteristics of a detection system augmented by a TDLMS prewhitening filter are plotted using Monte-Carlo techniques. It is shown that such a detector has better operating characteristics than a conventional matched filter in the presence of correlated clutter. For very low signal-to-background ratios, TDLMS-based detection systems show a considerable reduction in the number of false alarms. The output energy in both the residual and prediction channels of such filters is shown to be dependent on the correlation length of the various components in the input signal. False alarm reduction and detection gains obtained by using this detection scheme on thermal infrared sensor data with known object positions is presented.

High precision alignment procedure for an ellipsometer.

Beam deviation in the polarizing elements is identified as a significant source of error in existing ellipsometer alignment procedures. A high precision alignment procedure that eliminates these errors is described. This procedure is less time consuming than previous methods, and its accuracy is comparable to the limit of resolution of the ellipsometer (typically 0.01-0.005 degrees ). A further advantage of this procedure is that it provides a precise method for the alignment of specimens and lasers with the ellipsometer.

Sensitivity of the Ellipsometric Parameters to Angle-of-Incidence Variations.

Formulas by which the partial derivatives of the ellipsometric parameters psi and Delta with respect to the angle of incidence can be calculated are presented. These derivatives are plotted as a function of the angle of incidence, the refractive indices of the film, the substrate, and the immersion medium, and also as a function of film thickness on three-dimensional graphs. These graphs illustrate the angular regions in which angle-of-incidence errors are significant for typical materials. At the angles of incidence at which these derivatives are large, errors due to beam deviation and errors due to the use of noncollimated light or due to the use of specimens with rough or irregular surfaces can be significant. The results illustrate that the errors due to beam deviation are often significant in zone-averaged measurements when standard optical components with wedge angle tolerances of 0 degrees 3' of arc are used.

Beam deviation errors in ellipsometric measurements; an analysis.

The types of error produced by beam deviation in the optical elements of an ellipsometer are examined. It is shown that there are two types of error that may be significant-systematic errors due to a variation in the plane of incidence and in the angle of incidence at the specimen and errors due to the combined effects of beam displacement and nonuniformities in either the detector response or the optical properties of the specimen, the compensator, the polarizer, the analyzer, or the specimen cell. Analytic expressions for the variation in the plane of incidence and in the angle of incidence are given in terms of parameters that can be determined experimentally. A method by which these parameters can be measured is described. It is shown that the azimuthal variation in the angle of incidence produces fundamental errors in conventional zone averaging techniques because the values of psi and Delta are averaged at different angles of incidence in different zones. Methods of experimentally predetermining when such errors are likely to be significant are discussed, and a procedure that cancels most systematic errors due to beam deviation in each zone is described. The combined effects of beam deviation in the polarizer, the compensator, the cell windows, and the analyzer are considered in several commonly used configurations, and the configurations that minimize beam deviation errors are described.