Abstract: The invention provides both a method and apparatus that measures a property of a structure that includes at least one layer. The apparatus features a laser (e.g., a microchip laser, described below) that generates an optical pulse, and a diffractive mask that receives the optical pulse and diffracts it to generate at least two excitation pulses. An optical system, (e.g., an achromat lens pair) receives the optical pulses and spatially and temporally overlaps them on or in the structure to form an excitation pattern that launches an acoustic wave. The acoustic wave modulates a property of the structure, e.g., it generates a time-dependent “surface ripple” or modulates an optical property such as the sample's refractive index or absorption coefficient. Surface ripple is defined as a time-dependent change in the morphology of the surface; its peak-to-null amplitude is typically a few angstroms or less.

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: An optical configuration that provides tunable characteristics. The tunable characteristics are applicable, for example, for channel monitoring, dispersion compensation and polarization-dependent loss. A passive optical element is used where the optical properties of this element varies as a function of position on the element.

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: The present invention relates to a heterodyne interferometer system with a pre-processing of the target signal to isolate and remove self-interference signals using a known phase modulation of the carrier signal's frequency. Where self-interference signals do not include a time delay inherent in the target signal that travels to the target reflector, by selecting a modulation frequency tuned to the time delay and then filtering the resultant signal the target beam can be isolated and the self-interference signal can be effectively removed The system includes a modulation unit to apply a phase modulation to the carrier signal, and a mixing unit that demodulates the target signal at the modulation frequency to isolate the target beam.

Abstract: Topographic measurement of eye structures based on short coherence interferometry is the subject of the invention. The problem occurring in this connection is that longitudinal and transverse eye movements during signal registration lead to errors in the measured structure. The influences of longitudinal eye movements are compensated in that the reference beam, independent from the measurement beam, is directed to the corneal vertex and is reflected at the latter. The influences of longitudinal eye movements are minimized in that the transverse position of the eye is monitored by means of a direction-dependent registration of the light reflected at the corneal vertex by means of a diode array or a four-quadrant diode and transverse misalignment is detected and compensated.

Abstract: A method of determination of a property of an optical device under test includes using a first initial coherent light beam, changing a first initial property of the first initial light beam, coupling the first initial light beam to the device under test, detecting a first signal of the first initial light beam received from the device under test, and correcting any a non-linearity in the first signal by interpolating the first signal on a linear scale.

Abstract: An aspheric microlens, particularly a conic constant of the microlens, may be evaluated and this evaluation may be used to determine an optimal process for creating the aspheric microlens. Such evaluation may include a curve fitting or a numerical expression of the wavefront.

Abstract: Techniques for performing phase-shifting interferometry are disclosed.

Abstract: This invention relates to an apparatus and method for positioning dual stages during semiconductor wafer processing. More particularly, the invention facilitates the use of interferometers to determine the positions of both wafer stages at all times during processing. While the movement of a typical twin stage apparatus causes one of the stages to eclipse the other and requires the addition of a significant number of additional interferometers, this invention minimizes the number of interferometers necessary through dimensioning the stages so that one stage never totally eclipses the other.

Abstract: A semiconductor ring laser gyro comprising two or more ring lasers, the ring lasers being optically independent of each other, is characterized in that a change in beat frequency with respect to a change in angular velocity of a first ring laser is opposite to that of a second ring laser, and angular velocity of rotation of the gyro is detected by a signal representing a difference between a first beat frequency generated by the first ring laser and a second beat frequency generated by the second ring laser.

Abstract: A wavefront measuring apparatus and a wavefront measuring method are capable of performing optical measurement on a test optical system, including an immersion optical system, with comparable ease of handling to that of the conventional measuring method using a concave member, and substantially independently of reflection that may occur at the surface closest to the test optical system among the surfaces of an optical member for reflecting light exiting from the test optical system. The wavefront measuring apparatus has a light source, a reference light path in which a reference member for producing reference light is disposed, and a test light path in which the test optical system is disposed. A plano-convex optical member with a wall thickness approximately equal to the radius of curvature of a convex surface thereof is disposed in the test light path in such a manner that a plane surface thereof faces toward the test optical system.

Abstract: An apparatus for detecting wavelength change of a first light signal comprises an amplitude splitting interferometer and a detector. The amplitude splitting interferometer comprises first and second optical paths. The first optical path has a first index of refraction that varies with wavelength over a first wavelength band. The second optical path has a second index of refraction that is relatively constant over the first wavelength band. In operation the first light signal enters and exits the amplitude splitting interferometer forming interference light. The interference light couples to the detector which detects the wavelength change of the first light signal from the interference light. An interferometer comprises a first beam splitter, third and fourth optical paths, and a second beam splitter. The third optical path is optically coupled to the first beam splitter and has a third index of refraction that varies with wavelength over a second wavelength band.

Abstract: A method, apparatus, and system for measuring optical phase and amplitude properties of an output optical field to characterize diffractive, refractive, and other optical elements to estimate, measure, and characterize an optical transfer function are disclosed herein. In a representative embodiment, a light source may generate an optical field incident to an optical element, such as a diffraction grating. An aperture plate may be positioned relative to the optical element to allow translation of at least one of the aperture plate or the optical element in a plane transverse to a surface normal of the optical element, resulting in an output optical field having spatially dependant amplitude and phase characteristics related to a position on the optical element and to the optical field incident to the optical element. The output optical field may then be detected and analyzed to characterize the optical transfer function of the optical element.

Abstract: A scanning interferometer employs dual interferometer modules at different wavelengths to expand a dynamic range of measurement, a compound probe for measuring multiple surfaces, and a confocal optical system for distinguishing between the surfaces measured by the compound probe. Within the compound probe, miniature optics divide a test beam into two sub-test beams that are focused normal to different test surfaces. Both sub-test beams contain the different wavelengths. A separate interferometer monitors movements of the compound probe for producing absolute measures of the test surfaces.

Abstract: A method for screening the quality of an optical component including the step of simulating the performance of the optical component. The step of simulating includes the step of measuring the optical phase &phgr; of the optical component, wherein the step of measuring comprises indirectly measuring the optical phase &phgr; of the optical component using a scanning laser having a scanning step size &Dgr;&ohgr; and a modulation frequency &ohgr;m such that &Dgr;&ohgr;/&ohgr;m≦2. The light throughput R of the optical component is then measured. A transfer function H as a function of optical frequency &ohgr; is constructed where H(&ohgr;)=R(&ohgr;)exp[j&phgr;(&ohgr;)], and the performance is simulated using the measured value of the optical phase and the light throughput into the transfer function.

Abstract: A phase shift fringe image analysis method comprises the steps of shifting an object to be observed and a reference relative to each other by using a phase shift device, obtaining fringe image data at three or more phase shift positions having a given phase gap therebetween, and determining a phase of the object by analyzing thus obtained plurality of fringe image data items. The positional data of at least three phase positions are specified, and the whole or part of the fringe image data on which carrier fringes at these phase positions are superposed is subjected to a predetermined arithmetic operation so as to carry out a phase analysis and determine the phase of the object.

Abstract: A method is provided for sensing an environmental effect upon a sensing element and includes exposing the sensing element into the environmental effect, producing a light signal in the sensing element, modulating the light signal with a modulation signal, and determining a path length of the light signal as a function of the modulation signal. A fiber optic sensor is provided that includes a light source producing a light, a sensing element optically coupled to the light source such that the light propagates through the sensing element, a detector optically coupled to the sensing element. The detector detects light intensity propagating in the sensing element. An electronics processor receives the detector output and produces a modulation signal for the light. The processor further produces an output signal indicative of the environmental effect as a function of the modulation signal.

Abstract: A Mach-Zehnder interferometer having two optical couplers interconnected by two optical fibers at least one of which is temperature insensitive. In use, temperature induced changes in the geometrical length and refractive index of the temperature insensitive fibers offset each other so that the optical path length of the fiber is unaffected by the temperature change. Where two temperature insensitive fibers are included these may be of the same or of different lengths. The interferometer may be used in a Dense Wavelength Division Multiplex system.

Abstract: The invention features an interferometry system that uses a small angular difference in the propagation directions of orthogonally polarized components of an input beam to an interferometer. The orthogonally polarized components define reference and measurement beams for the interferometer. The angular difference allows one to distinguish between the reference and measurement beam components of the input beam and facilitates the suppression of at least some of the cyclic errors caused by interferometer imperfections.