Surface inspection by amplitude modulated specular light detection
An 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. The first light beam portion illuminates the surface of the disk and produces a reflected light beam. An acoustic-optic deflector deflects the reflected light beam and the second light beam portion producing a deflected output beam having a deflection angle. A detector detects an incident beam translation signal corresponding to reflected light beam angular deflection and acoustic-optic deflector beam angular deflection from the deflected output beam.
1. An 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, the first light beam portion illuminating the surface of the disk and produces a reflected light beam;
an acoustic-optic deflector that deflects the reflected light beam and the second light beam portion producing a deflected output beam having a deflection angle; and
a detector that detects an incident beam translation signal corresponding to reflected light beam angular deflection and acoustic-optic deflector beam angular deflection from the deflected output beam.
2. The apparatus for detecting defects on a disk surface according to claim 1 , wherein the deflected output beam is based on an illumination spot size and a disk rotation speed.
3. The apparatus for detecting defects on a disk surface according to claim 1 , wherein the detector includes a prism mirror and photomultiplier tubes.
4. The apparatus for detecting defects on a disk surface according to claim 3 , further comprising a differential amplifier, a summation amplifier and a divider network.
5. The apparatus for detecting defects on a disk surface according to claim 4 , wherein output signals from the photomultiplier tubes are differentially summed and normalized by the differential amplifier, the summation amplifier and the divider network.
6. The apparatus for detecting defects on a disk surface according to claim 5 , wherein the summed and normalized signal is amplitude modulated by a disk surface circumferential slope.
7. The apparatus for detecting defects on a disk surface according to claim 1 , wherein the light source is fiber optic coupled with polarization maintaining fibers.
8. The apparatus for detecting defects on a disk surface according to claim 1 , further comprising a plano-convex lens providing an illumination spot on the surface of the disk.
9. The apparatus for detecting defects on a disk surface according to claim 1 , wherein the acoustic-optic deflector is driven with a frequency chirped wave.
10. The apparatus for detecting defects on a disk surface according to claim 1 , further comprising a lens that collimates the deflected output beam from the acoustic-optic deflector.
11. A method for detecting defects on a disk surface, comprising:
generating a light beam;
splitting the light beam into a first light beam portion and a second light beam portion, the first light beam portion illuminating the surface of the disk which produces a reflected light beam;
deflecting the reflected light beam and the second light beam portion to produce a deflected output beam having a deflection angle; and
detecting an incident beam translation signal corresponding to reflected light beam angular deflection and acoustic-optic deflector beam angular deflection from the deflected output beam.
12. The method for detecting defects on a disk surface according to claim 11 , wherein the deflected output beam is based on an illumination spot size and a disk rotation speed.
13. The method for detecting defects on a disk surface according to claim 11 , further comprising summing and normalizing the detected incident beam translation signal.
14. The method for detecting defects on a disk surface according to claim 13 , wherein the summed and normalized signal is amplitude modulated by a disk surface circumferential slope.
15. The method for detecting defects on a disk surface according to claim 11 , further comprising providing an illumination spot on the surface of the disk.
16. The method for detecting defects on a disk surface according to claim 11 , further comprising generating the deflection angle with a frequency chirped wave.
17. The method for detecting defects on a disk surface according to claim 11 , further comprising collimating the deflected output beam.
18. A system 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, the first light beam portion illuminating the surface of the disk and produces a reflected light beam;
an acoustic-optic deflector that deflects the reflected light beam and the second light beam portion producing a deflected output beam having a deflection angle;
a detector that detects an incident beam translation signal corresponding to reflected light beam angular deflection and acoustic-optic deflector beam angular deflection from the deflected output beam; and
a processor coupled to the detector that determines the presence of a defect based on the incident beam translation signal.
19. A system for detecting defects on a disk surface according to claim 18 , wherein the deflected output beam is based on an illumination spot size and a disk rotation speed.
20. A system for detecting defects on a disk surface according to claim 18 , wherein the detector includes a prism mirror and photomultiplier tubes.