Abstract: Optical system for measuring surface topography, comprised of a light source (30), a diffractive optical assembly (70,72,73) comprised of two or more diffraction gratings, holograms or like diffractive optics (120, 130;122, 132;123, 133), electronic detection means and digital signal processing means (10, 110) for determining surface height from interference data. The diffractive optical assembly (70,72,73) divides the incident light into two beams (150,160;152,162;153,163), which subsequently impinge upon the object (20) at the same place on the object surface (70) but at two different angles of incidence. After reflection from the object surface, the beams pass separately back through the diffractive optical assembly (70,72,73), after which they combine once again and form an interference pattern representative of the surface topography. The equivalent wavelength of the resultant interference pattern is much greater than the illumination wavelength.

Abstract: A method and system for measuring the phase difference between two orthogonally polarized components of a test beam as well as the intensities of these two components. A partially-polarizing beamsplitter (101) divides a polarized test beam (103) into first and second spatially-separated beams (154,104). The first beam (154) passes through a wave plate (160) oriented so as to retard the phase of the s polarization component with respect to the p polarization component. The first beam (154) then passes through a first polarizing beamsplitter (155), to produce a first pair of spatially separated output beams (156,157) with mutually-orthogonal linear polarizations. The second beam (104) is likewise passed through a second polarizing beamsplitter (105) to produce a second pair of linearly-polarized output beams (106,107). Photodetectors (108,109,158,159) send an electrical signals proportional to the intensities of the beams (106,107,156,157) to a computer (99).

Abstract: An apparatus and method for measuring and compensating for birefringence in a rotating ground glass disk (20) such as are employed in polarization based optical flying height testers. The polarized light (1, 3) impinges on the top surface (24) of the disk (20) and is refracted through the disk to a measurement point (90) on the opposite surface (25) from which it is reflected back through the disk (20) and refracted before it exits the disk (20) in a beam (9) containing both s aand p polarizations which are detected by a phase detector (13) which measures any difference in phase between the s and p polarizations. Any variation of the phase .theta..sub.G with respect to the position defined by the measurement point provides the birefringence parameters b.sub..parallel.,b.sub..perp. for the positions on the disk (20). The phase detector (13) measures the phase .theta..sub.G at a skew angle .zeta.

Abstract: Optical method and means for high-speed characterization of the distance between a substantially transparent plane-parallel disk (20) in rotation about an axis (21) perpendicular to its largest surface, and a substantially flat object (30) that is nearly in contact with the disk surface (25). A collimated light beam (2) is first divided into two parallel, spatially separated and orthogonally polarized beams (5,7) which are incident upon the disk surface (25) at Brewster's angle. One beam (5) passes through the disk unreflected and impinges upon the surface of object (30) and reflects back from object (30). The other beam (7) is partially reflected from the bottom surface of the disk (25) and is subsequently recombined with beam (5) and caused to interfere. Optical means (90,91,100,110,150) together with electronic detection and analysis means (130,131; 120,121; 99) determine the phase of the interference.

Abstract: A method and system for profiling an object surface at a convenient working distance to the object using desensitized interference images. The optical profiler system comprises a desensitized interferometer characterized by an equivalent wavelength much longer than the wavelength of the source light, a mechanical scanning system, and electronic detection and data processing means. Data for one or more image points or pixels in the field of view of the interferometer are generated by displacing the object with respect to the interferometer while at the same time recording detecter data in electronic memory. The variation of intensity as a function of scan position may be described as an approximately oscillator signal related to the equivalent wavelength, modulated by a signal envelope that limits the interference effect to a range within the equivalent coherence length. The oscillatory signal corresponds to interference fringes, and the envelope is the fringe contrast.

Abstract: An optical radar system includes a laser diode and an external cavity formed by a partial reflector for reflecting a first portion of the laser beam back into the diode. A second portion of the beam is passed out of the external cavity for backscatter thereof from a target back into the diode. The emission thereby has a beat frequency related to the velocity of the target. A frequency chirp is introduced by mechanically oscillating the partial reflector longitudinally resulting in a modulation frequency in the emission corresponding to the range of the target. A photodetector and processor are used to determine the velocity and range.

Abstract: Optical method and means for high-speed measurement of the distance between two surfaces, the first of which (25) is part of a substantially transparent element (20) and the second of which (35) is part of a test object (30). In a first step, a lens (3) directs a light beam (2) through a polarizing component (4) towards the first surface at an oblique angle of incidence. In a next step, the polarized light beam (5) reflects back through the transparent element by means of the combined effect of reflections from the first surface of the transparent element and from the surface of the test object (30). In a further step, a polarization-sensitive intensity detector (12) and a phase detector (13) measure the strength and relative phase of the polarization components defined by the plane of incidence. A computer (99) then analyzes these measured parameters to determine the size of the gap between the two surfaces (25,35).

Abstract: Optical system for measuring surface topography, comprised of a light source (30), a diffractive optical assembly (70, 72, 73) comprised of two or more diffraction gratings, holograms or like diffractive optics (120, 130; 122, 132; 123, 133), electronic detection means and digital signal processing means (10, 110) for determining surface height from interference data. The diffractive optical assembly (70, 72, 73) divides the incident light into two beams (150, 160; 152, 162; 153, 163), which subsequently impinge upon the object (20) at the same place on The object surface (70) but at two different angles of incidence. After reflection from the object surface, the beams pass separately back through the diffractive optical assembly (70, 72, 73), after which they combine once again and form an interference pattern representative of the surface topography. The equivalent wavelength of the resultant interference pattern is much greater than the illumination wavelength.

Abstract: An optical system for measuring the front and back surface topography of transparent objects with substantially parallel surfaces includes an interferometer, an electronic camera, and digital signal processing means for determining surface height from interference data. The several disclosed methods of the invention permit the mathematical separation of the interference contributions due to the multiple reflections from the two parallel surfaces of the object. These methods involve relatively simple procedures, such as reversing the orientation of the object between two successive interference measurements, followed by mathematical analysis or calculations that may be readily performed by computer. The preferred apparatus includes a tunable laser source that is used to remove undesirable artifacts and improve the quality of the final image.

Abstract: A system for measuring surface topography with notably decreased sensitivity to errors in phase and phase interval calibration and to the presence of low-frequency vibration during data acquisition includes an optical interferometer for developing interference data from the surface to be profiled, an electronic imaging system or camera for receiving the interference data, an arrangement for variably adjusting the reference phase of the interferometer illumination, and a digital signal processing device or computer for determining surface height from the interference data. A sequence of seven intensity images are detected by the imaging system and stored electronically. The intensity images correspond to interference patterns for seven different reference phase values spaced at intervals of approximately .pi./2. The images are processed by the computer so as to recover the surface topography.

Abstract: An optical system for measuring the topography of an object includes an interferometer with a multiple-color or white-light source, a mechanical scanning apparatus for varying the optical path difference between the object and a reference surface, a two-dimensional detector array, and digital signal processing apparatus for determining surface height from interference data. Interferograms for each of the detector image points in the field of view are generated simultaneously by scanning the object in a direction approximately perpendicular to the illuminated object surface while recording detector data in digital memory. These recorded interferograms for each image point are then transformed into the spatial frequency domain by Fourier analysis, and the surface height for each corresponding object surface point is obtained by examination of the complex phase as a function of spatial frequency.

Abstract: A laser system includes a multimode laser diode positioned at a range from a target. Backscatter from the target returns into the diode and to modify the emission. An induced modulation frequency in the emission effects oscillatory mode transitions to create an amplitude modulation in mode power for a selected mode, the mode being selected by an optical spectrum analyser or an interference filter. The diode is positioned initially for a minimum in the amplitude modulation, and readjusted by a selected increment in response to an incremental change in target position so as to reestablish the amplitude modulation to the minimum. The incremental change thereby equals the selected increment.