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Proceedings Paper

A Scanning Differential Intensity And Phase System For Optical Metrology
Author(s): R. K. Appel; M. G. Somekh; C. W. See
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Paper Abstract

Most optical systems currently in use utilize a single type of measurement from which deductions are made about sample properties such as surface profile or reflectivity variations. In this paper we will present a system which can perform several independent measurements simultaneously. A Bragg cell is used to divide an incident light beam into two probing beams which are focussed onto the sample as two close spots. Independent measurement of differential phase and intensity is enabled by virtue of the Bragg cell introducing a frequency shift between the two beams and modulating the two in phase quadrature. By varying the frequencies in the Bragg cell drive, the separation of the spots may be changed, giving the system two distinct modes of operation, for imaging and metrology. The system is common path thereby giving considerable improvement in sensitivity over conventional interferometers which are limited by mechanical vibrations. A thorough description is given of the system which, together with computer simulations of the acoustooptic interaction, is used to quantify the performance of the system and to outline design considerations. Throughout the paper, emphasis is placed on identifying and describing problems which may be encountered in a practical implementation of the system.

Paper Details

Date Published: 20 December 1989
PDF: 12 pages
Proc. SPIE 1164, Surface Characterization and Testing II, (20 December 1989); doi: 10.1117/12.962829
Show Author Affiliations
R. K. Appel, University College London (England)
M. G. Somekh, University College London (England)
C. W. See, Rank Taylor Hobson Ltd. (England)

Published in SPIE Proceedings Vol. 1164:
Surface Characterization and Testing II
John E. Greivenkamp; Matthew Young, Editor(s)

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