US 5,517,307 A · Probe measurement apparatus using a curved grating displacement interferometer

Abstract

Apparatus for surface measurement has a grating interferometer with a curved diffraction grating carried on a pivotal support arm of a probe for contacting a surface. The probe is biased into contact with a surface by an electromagnetic coil acting on an armature, or a pair of such biasing arrangements. A laser diode illuminates the grating to produce a pair of first order diffracted beams of opposite sign which are reflected from internal faces of a prism, and combined by a diachronic central layer of the prism and a pair of beam splitters. Output signals from the beam splitters are supplied to a signal processing circuit having a fringe counter and an interpolator. The fringe counter detects zero crossings of the signals and the interpolator maintains a digital estimate of the phase of the signals and updates the estimate when the phase difference between the estimate and the input signals exceeds a predetermined threshold. The interpolator has a digital counter for providing low order bits of the digital output signal. The output of the fringe counter provides the high order bits.

Claims44

Dependent claims

Apparatus for measuring surface characteristics comprising:

a probe for contacting a surface to be measured;
a probe support carrying the probe for allowing pivotal movement of the probe about a pivot axis;
and
a grating interferometer for providing a measurement of pivotal movement of the probe, the interferometer comprising a diffraction grating disposed on a curved surface coupled to the probe support and having a center of curvature located at the pivot axis.

1 more element

Interferometer apparatus comprising:

light beam source means for providing a light beam;
a diffraction grating for receiving the light beam from the light beam source means to produce first and second diffracted beams of equal and opposite order;
and
a prism comprising
a central place for reflecting light in a first polarization plane and transmitting light in a second polarization plane,
a surface for receiving the first and second diffracted beams from the diffraction grating,
a pair of first and second side surfaces symmetrically disposed about the central plane for reflecting the first and second diffracted beams respectively to the central plane whereby a first combined beam is formed by a first polarization plane light of the first reflected diffracted beam reflected by the central plane and a second polarization plane light of the second reflected diffracted beam transmitted by the central plane and a second combined beam is formed by the second polarization plane light of the first reflected diffracted beam transmitted by the central plane and the first polarization plane light of the second reflected diffracted beam reflected by the central plane,
a first exit face for allowing the first combined beam to pass from the prism to a first analyzer, and
a second exit face for allowing the second combined beam to pass from the prism to a second analyzer, and
wherein the light beam source means is positioned to direct the light beam along a direction parallel to the central plane of the prism so that the light beam is incident on the diffraction grating without prior reflection within the prism.

7 more elements

Dependencies are inferred from the claim text.

Probe measurement apparatus using a curved grating displacement interferometer

Life of this patent

Probe measurement apparatus using a curved grating displacement interferometer

Life of this patent

Abstract

Claims44