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Multi-Wavelength, Spatially-Resolved Optical Profilometer

IP.com Disclosure Number: IPCOM000040865D
Original Publication Date: 1987-Feb-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Tzeng, HM: AUTHOR

Abstract

A method is described for making highly sensitive, spatially- resolved surface flatness measurements by utilizing multi-waveleng light sources to deduce surface flatness based on the Michelson interferometric principle.

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Multi-Wavelength, Spatially-Resolved Optical Profilometer

A method is described for making highly sensitive, spatially- resolved surface flatness measurements by utilizing multi-waveleng light sources to deduce surface flatness based on the Michelson interferometric principle.

The method can be carried out by using a tunable dye laser as the multiple wavelength light source. The collimated laser beam 1 is divided by beam splitter 2 and directed to the test surface S and the reference surface R. The two reflected beams are collected and imaged by cylindrical lens 3 onto the entrance slit 4 of a spectrograph 5. The longitudinal axis of the cylindri cal lens 3 is aligned with the entrance slit 4. The spectrograph 5 is equipped with a TV camera 6 at the exit plane. The dispersed wavelength is displayed along the horizontal axis while the spatial integrity of one stripe of the test surface (z direction) is carefully maintained in the vertical axis as shown in the Figure.

The maximum height variation (Ws) detectable is determined by two quantities: the free spectral range (Wg)fsr and the wavelength coverage of the multichannel detector system. The free spectral range between adjacent interferences (m and m - 1) is found to be

(Image Omitted)

Apparently, the free spectral range can be adjusted by the operating conditions. However, the wavelength coverage is predetermined by the detector employed and the specific grating installed in the spectrograph. Therefore, once the...