Patent ID: 6741357
Filing Date: 2004-05-25
Classification: G01B

Abstract:
An interferometer for disc surface inspection, comprising:a laser configured to provide a linearly polarized laser beam; a variable ratio beam splitter positioned to receive the linearly polarized laser beam and configured to split the linearly polarized laser beam into a reference beam and an object beam, the reference beam and the object beam being polarized beams with polarizations orthogonal to one another; a mirror posItioned to reflect the reference beam back toward the variable ratio beam splitter to provide a reflected reference beam; the disc surface positioned to reflect the object beam back toward the variable ratio beam splitter to provide a reflected object beam; the variable ratio beam splitter positioned to receive the reflected reference beam and the reflected object beam and configured to combine the reflected reference beam and the reflected object beam to provide a combinative beam; a non-polarizing beam splitter positioned to receive the combinative beam and configured to split the combinative beam into a first output beam and a second output beam; an adjustable quarter-wave plate positioned to receive the first output beam and configured to introduce a phase shift between the reflected object beam portion of the first output beam and the reflected reference beam portion of the first output beam to provide a phase-shifted output beam; a first polarizer positioned to receive the phaseshifted output beam and configured to assemble the reflected obiect beam portion and the reflected reference bea portion of tcomponents of the phase-shifted output beam along a predetermined direction to provide a first assembled beam; a second polanzer positioned to receive the second output beam and configured to assemble the reflected obiect beam portion and the reflected referencebeam portion components of the second output beam along the predetermined direction to provide a second assembled beam; a first optical detector positioned to receive the first assembled beam and configured to provide a first voltage proportional to change in intensity due to interference of the reflected object beam portion and the reflected reference beam portion of the first assembled beam; a second optical detector positioned to receive the second assembled beam and configured to provide a second voltage proportional to change in intensity due to interference of the reflected object beam portion and the reflected reference beam portion of the second assembled beam; and an information processingsystem coupled to the first optical detector and the second Wotical detector so as to receive the first voltage and the second voltage and for comparing the first voltage and the second voltage to determine out-of-plane displacements between the mirror and the disc surface as a function of phase change in the output beams.