Abstract: The invention features an interferometry system for a measuring a surface profile or thickness of a measurement object.

Abstract: Low coherence illumination is used in interferometric methods and systems which exhibit improved precision and flexibility. According to a first aspect of the invention, both a phase shifting interferometry (PSI) analysis and a scanning white light interferometry (SWLI) analysis are applied to a single 3D interferogram. This allows the precision of PSI to be achieved without being limited by the 2.pi. phase ambiguity constraint. According to another aspect of the invention, a position of a contrast peak of a broad-band 3D interferogram is located by calculating a single Fourier transform coefficient, using the Fourier transform coefficient to determine an analytic equation which corresponds to the derivative of the visibility function, and locating the peak contrast position by setting the derivative equal to zero. The use of analytic equation contrast peak detection improves accuracy and computational efficiency.

Abstract: Interference data is acquired as a sequence of pairs of adjacent acquisition intervals in relative quadrature separated by non-acquisition intervals of known, typically constant, phase. The interval pairs in quadrature straddle interline transfer events of the imaging device, such that the two intervals of a given pair are separated only by the very short time interval of an interline transfer event. As a result, the two intervals are acquired serially but almost simultaneously. Preferably four quadpairs are acquired in a measurement, with the phase separation between the pairs being nominally an odd multiple of .pi./2. Because the intervals of each pair are acquired nearly simultaneously and in quadrature, the interference data exhibits similar favorable characteristics exhibited by simultaneous phase quadrature interference data. Namely, when phase calculations are performed using the interference data, ripple error associated with vibrational disturbances tends to cancel out.

Abstract: Low coherence illumination is used in interferometric methods and systems which exhibit improved precision and flexibility. According to a first aspect of the invention, both a phase shifting interferometry (PSI) analysis and a scanning white light interferometry (SWLI) analysis are applied to a single 3D interferogram. This allows the precision of PSI to be achieved without being limited by the 2.pi. phase ambiguity constraint. According to another aspect of the invention, a position of a contrast peak of a broad-band 3D interferogram is located by calculating a single Fourier transform coefficient, using the Fourier transform coefficient to determine an analytic equation which corresponds to the derivative of the visibility function, and locating the peak contrast position by setting the derivative equal to zero. The use of analytic equation contrast peak detection improves accuracy and computational efficiency.

Abstract: A method and improved system for automatically and substantially simultaneously focusing and orienting an interferometric optical system, such as an interferometric microscope (25) illuminated by broad-band light, with regard to a surface under test (66), for providing a best focus and orientation of objects to be measured. The optical system (20, 25, 30, 35, 37, 60, 40) includes a pixel array, such as a sparse array (30) onto which an interferogram is imaged. The pixel array (30) is scanned (20, 25) for detecting a peak fringe contrast for the pixels in the array (30) and the scan position at the detected peak fringe contrast for each pixel int he array (30) is saved (40).

Abstract: A method and system for providing interferometric measurements having reduced sensitivity to vibrations. An interference pattern from an interferometer (35) is amplitude split into first and second interferograms and imaged onto first and second detectors (10, 11), respectively, such as CCD cameras (10, 11). The two cameras (10, 11) have different data acquisition rates. The frame integration period of the slow detector is distinctly shorter than that of the fast detector. The detectors (10,11) are disposed such that the image fields substantially overlap and are synchronized with each other for enhancing vibration insensitivity. The shorter the integration period of the slow detector with respect to the fast detector, the greater the vibration insensitivity. During data acquisition a phase shifter (45) changes the phase difference between the beams in the interferometer (35) while data from both cameras (10, 11) is taken by a frame grabber (15) and saved in a computer (25).

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 providing interferometric measurements having reduced sensitivity to vibrations. An interference pattern from an interferometer (35) is amplitude split into first and second interferograms and imaged onto first and second detectors (10,11), respectively, such as CCD cameras (10,11). The two cameras (10,11) have different data acquisition rates, such as a fast:slow camera ratio of at least 2:1, and are so disposed such that the image fields substantially overlap and are synchronized with each other so that the frame integration periods are identical and overlap in time. During data acquisition a phase shifter (45) changes the phase difference between the beams in the interferometer (35) while data from both cameras (10,11) is taken by a frame grabber (15) and saved in a computer (25).

Abstract: A method and apparatus for producing a repeatable motion profile from a biased piezoelectric transducer (28) in which a first set of stored calibration voltage values corresponding to points in a predetermined voltage profile on the transducer (28) are retrievably accessed from a random access memory (20) by sequentially addressing (30,32,34) the memory (20) in order to drive the piezoelectric transducer (28) with the retrievably accessed calibration voltage values. Gain current values associated with motion of the piezoelectric transducer (28) at the same measurement points on the voltage profile associated with the stored values are measured (48,50,52) and compared against the stored calibration values and any differences are corrected for in order to produce the repeatable motion profile. The measurement points are preferably in a region of constant rate of change of voltage in the voltage profile, such as corresponding to the crossover point (54) in a motion profile of linear slope.

Abstract: A method of profiling a rough surface of an object includes the steps of producing an interference pattern of the object surface using an interferometer to produce an illumination intensity on the pixels of an imaging device, varying the optical path difference between the object surface and a reference surface of the interferometer through a range including a position of zero optical path difference for each pixel, calculating values of an interference discriminator function to identify the regions of coherence, gathering at the imaging device and storing for each pixel a plurality of intensity values about the region of coherence--as identified by the state or value of the interference discriminator function calculations--at consecutive data points spaced along the range by a predetermined phase difference, storing for each pixel the relative position of the plurality of intensity values along the range, and calculating from the stored intensity values the difference in height between two selected pixels us

Abstract: The high intensity illuminator of the invention includes a mounting fixture, a receiving surface spaced from the mounting fixture, and a plurality of semiconductor illumination sources which are implemented, most preferably, by light emitting diodes or laser diodes. Each illumination source is operable for emitting an outwardly-diverging illumination cone along an axis of illumination of the source at a predetermined illumination wavelength. The plural illumination sources are mounted on the mounting fixture such that their illumination cones are overlappingly coincident on a selected portion of the receiving surface to provide at the receiving surface portion a highly uniform illumination of high intensity at the predetermined wavelength.

Abstract: A method and apparatus for removing the deleterious effects of interference on the focus error signal when focusing interferometric optical systems using triangulation or astigmatic techniques. These interference effects are eliminated by using the phase relationship between the differential error signal and the total intensity of the beam incident on the differential detector to identify and recover a unique focus position of a surface under test.

Abstract: An apparatus for sensing and measuring translational and rotational motion of an object, such as a gun barrel during a firing event, includes a pair of support boards attached in orthgonal relation on the object and a pair of elongated position sensitive detectors mounted in spaced relation to one another and in a common plane on each of the boards. The detectors have respective light sensitive axes oriented parallel. Also, electrical circuits are coupled to the detectors to produce bipolar output signals representative of the magnitude and direction of displacement of the positions of planar light beam impingement across the detector axes from zero rest positions thereon such that separate measurements of translational motion and rotational motion of the object with respect to imaginary axes extending through the zero rest positions of and perpendicular to the sensitive axes of the pairs of detectors can be derived therefrom.

Abstract: A unique electronic sensing screen apparatus for automatically measuring various parameters of moving projectiles. Projectiles pass between an artificial or natural light source and light sensors, resulting in signals from the sensors, which are processed into data showing projectile profiles or photo-like images, shock waves, velocity, angle of attack, and dispersion. The apparatus provides quick turn-around times between parameter measurements, such as those of many projectiles fired in rapid succession, and readily usable results.