Abstract: Methods and devices for inspecting and calibrating a stereoscopic imaging device, such as a binocular endoscope. In one exemplary embodiment, the method of the present invention measures a fringe pattern from light emitted through two channels of the device. An angle of each of the fringe pattern can be measured so as to allow a diopter difference between the channels to be calculated.

Abstract: The invention relates to an apparatus for performing electronic shearography on a test object, especially a tire or retread tire. The apparatus uses a laser light source to illuminate the test object. An optical element through which electromagnetic radiation is reflected from the test object is transmitted and forms a random interference image. The random interference image can be electronically processed to provide a video animation of the effects of stress on the test object. An archive memory can be provided for retaining the animation data which can be compressed such that it includes only preselected individual shearogram images from the set of sequential shearogram images and less than all of the image data associated therewith. An air handling system can be provided for changing the ambient pressure in a pressure chamber within which the test object is supportable. The air handling system can include a humidity reducing mechanism.

Abstract: Interferometry system including a multiple-pass interferometer having reflectors to reflect at least two beams along multiple passes through the interferometer. The multiple passes include a first set of passes and a second set of passes. The reflectors have first alignments that are normal to the directions of the paths of the beams that are reflected by the reflectors. The two beams provide information about changes in a first location on one of the reflectors after the first set of passes, and provide information about changes in the first location and changes in a second location on the reflector after the second set of passes. The paths of the beams are sheared during the first set of passes and during the second set of passes if at least one of the reflectors has an alignment other than the first alignment.

Abstract: Interferometry system including a multiple-pass interferometer having reflectors to reflect at least two beams along multiple passes through the interferometer, the multiple passes including a first set of passes and a second set of passes, the reflectors having first alignments that are normal to the directions of the paths of the beams that are reflected by the reflectors, the paths of the beams being sheared during the first set of passes and during the second set of passes if at least one of the reflectors has an alignment other than the first alignment, and optics to redirect the beams after the first set of passes and before the second set of passes so that shear imparted during the second set of passes cancels shear imparted during the first set of passes.

Abstract: A method and an apparatus for determining the influencing of the state of polarization of optical radiation by an optical system under test, wherein radiation with a defined entrance state of polarization is directed onto the optical system, the exit-side state of polarization is measured, and the influencing of the state of polarization is determined by the optical system with the aid of evaluation of the exit state of polarization with reference to the entrance state of polarization. An analyser arrangement which can be used for this purpose is also disclosed. The method and the apparatus are used, e.g., to determine the influencing of the state of polarization of optical radiation by an optical imaging system of prescribable aperture, the determination being performed in a pupil-resolved fashion.

Abstract: A spatially modulated interferometer incorporates a beam shearing system having a plurality of reflective surfaces defining separate light paths of equal optical path length for two separate output beams. The reflective surfaces are arranged such that when the two beams emerge from the beam shearing system they contain more than 50 percent of the photon flux within the selected spectral pass band. In one embodiment, the reflective surfaces are located on a number of prism elements combined to form a beam shearing prism structure. The interferometer utilizing the beam sharing system of the invention includes fore-optics for collecting light and focusing it into a beam to be sheared, and a detector located at an exit pupil of the device. In a preferred embodiment, the interferometer has no moving parts.

Abstract: A portable nondestructive testing instrument uses high-speed phase-stepping shearography, and vacuum stressing, to produce images of disbonds, impact damage, or delaminations, in metal or composite structures. The invention is especially useful in the inspection of large areas where only external access is feasible, such as in large aircraft, space vehicles, boats, or civil engineered structures having multiple bond lines. The invention includes a novel combination of components and techniques, including a high-spatial-resolution CCD sensor, low-voltage piezoceramic phase stepping, rapid phase stepping, a fast phase calculation technique, a fast image smoothing technique, and an implementation of all of the above in a portable unit. Specially designed timing and control algorithms allow data acquisition, transfer, calculation, smoothing, and display at rates of up to two times per second.

Abstract: A lateral-shear interferometer utilizes two relatively thick glass plates bonded together in a single block with a tilted air gap between opposing inner surfaces. The thickness of the glass plates is selected to be sufficiently large to separate the output beams from the light reflected from the top and bottom surfaces of the block, thereby eliminating the need for antireflection coatings. The shear interferometer is combined with an external mirror mounted on a tilt stage actuated by a computer-controlled tilt actuator to perform phase-shifting interferometric analysis in conventional manner.

Abstract: In a method for determining wavefront aberrations for the characterization of imaging characteristics in an optical imaging system, the measurement results from two different measurement methods, which are carried out at successive times, are combined. In this case, at least some of the aberration parameters which are determined in the previous first measurement method are used as a given precondition for determining aberration parameters with the aid of the second measurement method, and are assessed accordingly. This results in a hybrid method, in which the strength of at least two measurement methods are used in a combined form, and specific weaknesses of any one method can be avoided.

Abstract: An optical flow monitor. Fluid flow is determined by correlating two interference signals produced by coherent laser beams passing through a flowing fluid at two spaced-apart paths. The distance between the two paths is known and the correlation of the two signals is used to determine the time required for the fluid to flow between the two paths. In a preferred embodiment actually built and tested by Applicant the correlation is made by having an operator monitor on an oscilloscope the intensities of interference fringes corresponding to each of the two beam paths. Intensity variations in the interference fringes are caused by the same turbulent eddies passing each of the two paths. These turbulent eddies cause fluctuations in the index of refraction of the fluid which produce similar patterns on the oscilloscope which are separated on the oscilloscope time scale by an amount corresponding to the distance between the two beam paths and the flow rate of the fluid.

Abstract: Methods and devices for inspecting and calibrating a stereoscopic imaging device, such as a binocular endoscope. In one exemplary embodiment, the method of the present invention measures a fringe pattern from light emitted through two channels of the device. An angle of each of the fringe pattern can be measured so as to allow a diopter difference between the channels to be calculated.

Abstract: In an interference measuring device, which includes: a coherent beam generating source; a sample to be measured; a lens system for forming an image of the sample to be measured on an observing plane; an interference element for splitting a coherent beam into two systems, and forming an interference image on the observing plane or a plane equivalent thereto; an image pickup element for picking up the interference image on the observing plane; and a calculating device having functions of capturing and storing the interference image converted to electric signals by the image pickup element, and determining the phase distribution changed by the sample to be measured from the interference image by calculation, wherein a means for removing the phase change distribution due to the interference element is provided.

Abstract: An electronic shearography system can measure deformation of an object and/or test the object for defects. Two laterally sheared images of the same object are produced by reflecting coherent light from the object, and directing rays, originating from different points on the object, into an image sensor. The rays become collinear, or nearly so, before entering the image sensor, where they produce a recordable interference pattern having a relatively low spatial frequency. The shearing effect comes from two mirrors, positioned to reflect light from the object. One mirror is partially reflective and the other mirror is totally reflective. The mirrors are arranged such that two laterally sheared images are formed, and the arrangement eliminates the need for further optical elements in performing the shearing. Thus, the invention simplifies the optical system, and increases its efficiency.

Abstract: A method serves the direct phase-angle measurement of radiation, in particular of light radiation which is reflected from a body. The body is exposed to coherent radiation. The radiation reflected from the body is imaged by an imaging optical system (6) in an image plane in which a sensor is located. A reference radiation generated in accordance with the shearing method is superimposed on the sensor. The phase of the radiation from the body is determined from the measurement signals of the sensor. To improve such a method, the imaging optical system (6) possesses a diaphragm (11) having one or two apertures (12, 13) (FIG. 2a).

Abstract: A lateral shearing interferometer wavefront sensor system (10) that employs a double-shear/full aperture approach to correct for branch points in the wavefront of an optical beam (24) that has been aberated. The wavefront sensor system (10) includes a lateral shearing interferometer (12) having a beam splitter (14) that splits the beam (24) into a first split beam (28) and a second split beam (26), a beam shifter (22) that shifts the first split beam (28) relative to the second split beam (26), and a beam combiner (16) that combines first shifted split beam (28) and the second split beam (26) into a combined beam (30). The combined beam (30) provides an interference pattern that includes a plurality of interfered beam portions (76, 78, 82, 84). A deformable mirror (72) includes a plurality of actuators (74) which deform the mirror (72) to correct the beam wavefront.

Abstract: Apparatus for measuring angular changes in the direction of travel of a light beam comprising at least one beam shearing assembly for separating, preferably orthogonally polarized, components of the light beam and introducing a lateral shear between them. An analyzer operates on the components to provide them with a common polarization state. A lens focuses the commonly polarized components of the light beam to a spot in a detector plane, and a detector operates to generate an electrical signal having a phase that varies in accordance with the angular change of the light beam in at least one plane. Electronic means receive the electrical signal, determines the phase therefrom, and converts the phase to the angular change in the direction of travel of the light beam.

Abstract: An improved phase-shifting point diffraction interferometer can measure both distortion and wavefront aberration. In the preferred embodiment, the interferometer employs an object-plane pinhole array comprising a plurality of object pinholes located between the test optic and the source of electromagnetic radiation and an image-plane mask array that is positioned in the image plane of the test optic. The image-plane mask array comprises a plurality of test windows and corresponding reference pinholes, wherein the positions of the plurality of pinholes in the object-plane pinhole array register with those of the plurality of test windows in image-plane mask array. Electromagnetic radiation that is directed into a first pinhole of object-plane pinhole array thereby creating a first corresponding test beam image on the image-plane mask array.

Abstract: A wavelength detector includes an optical structure receiving an input beam, the optical structure outputting at least two wavelength dependent two-beam interference signals. Each wavelength dependent two-beam interference signal has a different phase offset. A detector receives the at least two wavelength dependent two-beam interference signals and outputs an electrical signal representative of each wavelength dependent two-beam interference. A processor receives the at least two electrical signals from the detector and generates a composite control signal. The two-beam interference signals may be created by reflecting light off the two surfaces of the optical structure. The different phase offsets may be created by providing a stepped pattern on one of the surfaces of the optical structure. Phase shifting interferometry techniques may be used to determine the wavelength from the periodic signals.

Abstract: A lateral shearing interferometer wavefront sensor system (10) that employs a double-shear/full aperture approach to correct for branch points in the wavefront of an optical beam (24) that has been aberated. The wavefront sensor system (10) includes a lateral shearing interferometer (12) having a beam splitter (14) that splits the beam (24) into a first split beam (28) and a second split beam (26), a beam shifter (22) that shifts the first split beam (28) relative to the second split beam (26), and a beam combiner (16) that combines first shifted split beam (28) and the second split beam (26) into a combined beam (30). The combined beam (30) provides an interference pattern that includes a plurality of interfered beam portions (76, 78, 82, 84). A deformable mirror (72) includes a plurality of actuators (74) which deform the mirror (72) to correct the beam wavefront.

Abstract: A method for evaluating aberrations of an optical element such as optical head for use with an optical system such as DVD. In this method, light is transmitted through the optical element and then diffracted into 0, ±1, ±2, . . . order diffraction lights, for example. Among others, first and second lights (e.g., 0 and +1, 0 and −1, +1 and −1, or 0 and ±1 order diffracted lights) are overlapped to form an image shared by the first and second lights. Then, light intensity at first and second points in the shared image are detected. At this moment, light intensity at the first and second points are changed. Then, a phase difference in light intensity of between first and second points is determined. Using the phase difference, aberrations of the optical element are determined.

Abstract: An interferometry system includes an interferometer to split an input beam into a measurement beam and at least one other beam. The interferometer directs the measurement beam along a measurement path that includes at least two passes to a measurement object, and overlaps the measurement beam with the other beam after the measurement beam completes the at least two passes. The path of the measurement beam is sheared during the first and second passes when the measurement object moves along a direction orthogonal to a portion of the measurement path that contacts the measurement object. The interferometry system includes optics to redirect the measurement beam after the first pass and before the second pass so that shear imparted during the second pass cancels shear imparted during the first pass.

Abstract: A dual field of view optical system and a single, lower cost detector are utilized, rather than using a large CCD camera or multiple CCD cameras, to view a sample that has two or more small areas that need to be measured, which are too far apart to fall on the detector but are within the field of view of the objective, or to measure a long, narrow strip that is too long for the detector, but whose total area is less than the detector area. The dual field of view optical system is employed in a microscope which comprises: (1) an illuminator arm with an illumination source and a field stop, (2) a beam splitter, (3) an objective, (4) a sample plane for location of a sample to be observed, and (5) a detector arm, with the illuminator arm configured to illuminate the sample plane through the beam splitter and the objective and with the detector arm configured to receive an image of the sample and including the dual field of view optical system.

Abstract: A differential interference contrast (DIC) microscope system is provided comprising: (a) an illumination source for illuminating a sample; (b) a lens system for viewing the illuminated sample, including an objective, defining an optical axis; (c) a DIC prism having a shear angle for separating an input light beam into two, orthogonally polarized output beams that are separated by the shear angle; (d) at least one detector system for receiving a sample image; (e) a mechanism for modulating the phase of the DIC image; (f) a mechanism for selecting the wavelength of light used in acquiring at least two sets of DIC data taken in a single shear direction; and (g) a mechanism for manipulating the multiple DIC data sets to synthesize data that appear to have been taken at a longer synthetic wavelength. The various approaches disclosed and claimed herein permit the measurement of surfaces with a greater slope than is possible with a single wavelength or shear distance.

Abstract: The invention relates to an apparatus for performing electronic shearography on a test object, especially a tire or retread tire. The apparatus uses a laser light source to illuminate the test object. An optical element through which electromagnetic radiation is reflected from the test object is transmitted and forms a random interference image. The random interference image is electronically processed to provide a video animation of the effects of stress on the test object.

Abstract: An optical monitoring instrument monitors etch depth and etch rate for controlling a wet-etching process. The instrument provides means for viewing through the back side of a thick optic onto a nearly index-matched interface. Optical baffling and the application of a photoresist mask minimize spurious reflections to allow for monitoring with extremely weak signals. A Wollaston prism enables linear translation for phase stepping.

Abstract: A lens inspection system for evaluating an objective lens system of an optical data recording/reproducing device by measuring a wave front of a light beam emerged from the objective lens system is provided with a laser source and a conversion lens. A laser beam is emitted by the laser source, and is incident on the objective optical system of the optical data recording/reproducing device. Further provided is an interferometer for measuring the wave front. A numerical aperture of an objective lens of the interferometer is smaller than a numerical aperture of the objective lens system of the optical data recording/reproducing device. The conversion lens receives the light beam emerged from the objective lens system of the optical data recording/reproducing device and emerges a light beam to the objective lens of the interferometer such that all the light beam emerged from the conversion lens enters the objective lens of the interferometer.

Abstract: The invention relates to an apparatus for performing electronic shearography on a test object, especially a tire or retread tire. The apparatus uses a laser light source to illuminate the test object. An optical element through which electromagnetic radiation is reflected from the test object is transmitted and forms a random interference image. The random interference image can be electronically processed to provide a video animation of the effects of stress on the test object.

Abstract: In a phase-shifting point diffraction interferometer, different image-plane mask designs can improve the operation of the interferometer. By keeping the test beam window of the mask small compared to the separation distance between the beams, the problem of energy from the reference beam leaking through the test beam window is reduced. By rotating the grating and mask 45°, only a single one-dimensional translation stage is required for phase-shifting. By keeping two reference pinholes in the same orientation about the test beam window, only a single grating orientation, and thus a single one-dimensional translation stage, is required. The use of a two-dimensional grating allows for a multiplicity of pinholes to be used about the pattern of diffracted orders of the grating at the mask. Orientation marks on the mask can be used to orient the device and indicate the position of the reference pinholes.

Abstract: The invention relates to an apparatus for performing electronic shearography on a test object, especially a tire or retread tire. The apparatus uses a laser light source to illuminate the test object. An optical element through which electromagnetic radiation is reflected from the test object is transmitted and forms a random interference image. The random interference image is electronically processed to provide a video animation of the effects of stress on the test object.

Abstract: An improved lateral shearing interferometer system for use with an original optical wavefront and a displaced optical wavefront having a phase difference from the original optical wavefront is disclosed. It comprises a lateral shearing interferometer that responds to the original optical wavefront and the displaced optical wavefront and develops an optical interference pattern representative of the optical phase differences. An optical detector located at the focal plane of the optical interference pattern provides a selective array of electrical signals representative of separated portions of the interference pattern. A data processor is programmed to indicate the separated portions of said interference pattern, which has pixels in non-adjacent locations in odd rows and no pixels in even rows. The pixels correspond to locations of actuators for correcting the phase difference.

Abstract: Disclosed is an apparatus and method for inspecting or testing a sample using shearography techniques. A laser shearing interferometer includes: a source of coherent radiation, a line generator producing a line of coherent radiation from said source, a line scanner scans the line of coherent radiation over the sample, a shearing element generates two laterally displaced images of the sample, and phase stepper or ramper steps or ramps the phase of one of the two images. A video camera views images of the sample and provides corresponding video output signals. An image processor receives the video output signals and extracts therefrom the frame rate of the camera in substantially realtime. A signal generator provides the stepper and the line scanner, a signal substantially in phase with the frame rate of the camera, a decoder is used for phase extraction and a vacuum chamber contains the laser shearing interferometer and the sample under test.

Abstract: Interferometric methods are presented to facilitate alignment of image-plane components within an interferometer and for the magnified viewing of interferometer masks in situ. Fourier-transforms are performed on intensity patterns that are detected with the interferometer and are used to calculate pseudo-images of the electric field in the image plane of the test optic where the critical alignment of various components is being performed. Fine alignment is aided by the introduction and optimization of a global contrast parameter that is easily calculated from the Fourier-transform.

Abstract: The extreme ultraviolet (EUV) phase-shifting point diffraction interferometer (PS/PDI) provides the high-accuracy wavefront characterization critical to the development of EUV lithography systems. Enhancing the implementation of the PS/PDI can significantly extend its spatial-frequency measurement bandwidth. The enhanced PS/PDI is capable of simultaneously characterizing both wavefront and flare. The enhanced technique employs a hybrid spatial/temporal-domain point diffraction interferometer (referred to as the dual-domain PS/PDI) that is capable of suppressing the scattered-reference-light noise that hinders the conventional PS/PDI. Using the dual-domain technique in combination with a flare-measurement-optimized mask and an iterative calculation process for removing flare contribution caused by higher order grating diffraction terms, the enhanced PS/PDI can be used to simultaneously measure both figure and flare in optical systems.

Abstract: The invention relates to an apparatus for performing electronic shearography on a test object, especially a tire or retread tire. The apparatus uses a laser light source to illuminate the test object. An optical element through which electromagnetic radiation is reflected from the test object is transmitted and forms a random interference image. The random interference image is electronically processed to provide a video animation of the effects of stress on the test object.