Surface inspection by double pass laser doppler vibrometry

Details Surface inspection by double pass laser doppler vibrometry Surface inspection by double pass laser doppler vibrometry

2007-01-17

2009-06-30

Lee (Andrew), Hwa S (Department: 2886)

Optics: measuring and testing

By light interference

Having light beams of different frequencies

Reexamination Certificate

active

07554670

ABSTRACT:
A double pass apparatus for detecting defects on a disk surface includes a light source that generates a light beam and a beamsplitter that splits the light beam into a first light beam portion and a second light beam portion. A modulator is provided that modulates the second light beam portion into a frequency shifted modulated light beam for illuminating the surface of the disk. The frequency shifted modulated light beam is twice reflected from the surface of the disk, thus doubling the frequency shift of the reflected light beam. A polarizing beamsplitter combines the first light beam portion with the reflected light beam portion providing an interference signal.

REFERENCES:
patent: 5394233 (1995-02-01), Wang
patent: 6943894 (2005-09-01), Kitahara
A. Vanderlugt & A.M. Bardos;Design Relationships for Acousto-Optic Scanning Systems; Applied Optics; vol. 31, No. 20, Jul. 10, 1992.

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