A detection of the lateral position of a test pattern imaged onto a position sensitive detector is quite commonly used in a variety of different measurement applications. In the case of an electronic autocollimator, the position of the image of a reticle is determined to measure small angle changes of a tilted surface. In many cases CCD matrix or CCD line detectors are used as position sensing devices. Two different procedures for the detection of the position of the test pattern are compared taking into account modulations of the obtained image signal, caused by diffraction. Differences between the detection of the arithmetic mean value and the geometrical mean value of the intensity will be analyzed. The influence of different fill factors of the detector elements is calculated. To avoid unwanted modulations of the signal a suitable method or algorithm for the detection of the position as well as an optimized layout of the reticle has to be chosen. Binary and phase shifting reticle designs will be compared. It is shown that an optimized layout is able to largely compensate modulations while the image is laterally shifted in the plane of the detector. Due to a step by step description of the image formation and signal analysis the example given will be also of practical use.

Date Published: 18 June 2007
PDF: 8 pages
Proc. SPIE 6617, Modeling Aspects in Optical Metrology, 661703 (18 June 2007);

Published in SPIE Proceedings Vol. 6617:
Modeling Aspects in Optical Metrology
Harald Bosse; Bernd Bodermann; Richard M. Silver, Editor(s)