Fabry-Perot probe profilometer having feedback loop to maintain

Details Fabry-Perot probe profilometer having feedback loop to maintain Fabry-Perot probe profilometer having feedback loop to maintain

1995-03-23

1996-10-15

Turner, Samuel A.

Optics: measuring and testing

By dispersed light spectroscopy

Utilizing a spectrometer

356357, G01B 902

Patent

active

055659870

ABSTRACT:
This invention describes a surface profilometry system which measures the surface topography of a sample on a sub-nanometer scale. The surface profile is determined through measurement of the change in distance between two mirrors of a multi-pass resonant cavity that is referenced to a frequency stabilized laser source. The contact stylus is in contact with the sample as it is translated along the plane to be measured. As the stylus traverses the sample, it is vertically deflected and transfers the motion directly to one of the mirrors of a multi-pass resonant cavity. The cavity is referenced to a frequency stabilized laser source that is synchronized with the resonant modes of the multi-pass cavity. Very small sub-nanometer deviations of the cavity can be detected by monitoring the laser beam incident on the multi-pass cavity. There are two embodiments by which the cavity length changes can be measured. The first embodiment involves adding variable frequency sidebands onto the stabilized laser through the use of an optical modulator. As the resonant cavity changes length due to the motion of the stylus, the modulation frequency is varied so that the sideband is kept on resonance with the cavity mode. The second embodiment involves monitoring the direct output of the stabilized laser beam after reflection from the resonant cavity. A position actuator adjusts the length of the cavity to maintain the resonance condition between the cavity mode and the stabilized laser beam.

REFERENCES:
patent: 4153370 (1979-05-01), Corey
patent: 4717255 (1988-01-01), Ulbers
patent: 5193383 (1993-03-01), Burnham et al.
patent: 5225888 (1993-07-01), Selwyn et al.
patent: 5305330 (1994-04-01), Rieder et al.

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