| US 7,554,670 B2 | ||
| Surface inspection by double pass laser doppler vibrometry | ||
| Peter C. Jann, Santa Clara, Calif. (US); and Wafaa Abdalla, San Jose, Calif. (US) | ||
| Assigned to Seagate Technology LLC, Scotts Valley, Calif. (US) | ||
| Filed on Jan. 17, 2007, as Appl. No. 11/654,929. | ||
| Claims priority of provisional application 60/759756, filed on Jan. 18, 2006. | ||
| Prior Publication US 2007/0165239 A1, Jul. 19, 2007 | ||
| Int. Cl. G01B 9/02 (2006.01) | ||
| U.S. Cl. 356—487 | 18 Claims |
| 1. A double pass apparatus for detecting defects on a disk surface, comprising:
a light source that generates a light beam;
a beamsplitter that splits the light beam into a first light beam portion and a second light beam portion;
a modulator that modulates the second light beam portion into a frequency shifted modulated light beam for illuminating the
surface of the disk,
wherein the frequency shifted modulated light beam is twice reflected from the surface of the disk, doubling the frequency
shift of a reflected light beam;
a polarizing beamsplitter that combines the first light beam portion with the reflected light beam portion providing an interference
pattern; and
photomultiplier tubes that square law detect the interference pattern.
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