Abstract: The phase ambiguity of conventional interferometers may be removed by using two laser diodes of different optical frequency to generate a synthetic wavelength. However, the stability requirements for a two-color interferometric laser gauge that must provide unambiguous determination of the optical fringe order over a large distance can be severe. The invention determines upper limits on the optical wavelength uncertainity and expresses same as a function of optical path difference between object and reference beams, phase measurement errors and the synthetic wavelength. A wavelength stabilization arrangement involves simultaneous servo control of two laser diodes (10, 12) with a single Fabry-Perot etalon (36). An embodiment of the invention demonstrates its effectiveness for long-term stabilized two-color interferometry over a distance of 250 mm, with a 15 .mu.m synthetic wavelength and a repeatability of 40 nm. For periods of less than 1000 seconds, the repeatability is eight nm.

Abstract: The present invention concerns a measurement method of the alignment status of a shaft line (16) in rotating machineries and an apparatus for the implementation of the method. According to the invention, the displacement of alignment is measured at convenient points of the shaft line (16) from the displacement of an optically fanned laser beam (4) hitting sensor units (10, 11). At the beginning of a measurement session, a zero reference point is determined for the beam (4) and the measurement values of the sensor units (10, 11) are compared against this reference value during the measurement session. The relative displacement is obtained as the difference between the initial value and the value during the measurement. The apparatus and method is also applicable to the measurement of displacements in pipelines, long shafts and other similar systems.

Abstract: A laser interferometer for inspecting the surface condition of a specimen by irradiating the specimen on a specimen support mechanism with a laser beam projected thereto through a reference plate, and observing the interference fringe produced by interference between reflected light from a reference surface of the reference plate and a surface of the specimen under inspection, the laser interferometer includes: an interferometer housing accommodating therein an optical laser beam guide member and an optical interference fringe imaging member, and is provided with a laser beam guide portion in a wall portion thereof; a laser tube mount member of a cylindrical form projected on the outer side of the housing and positioned in such a manner so as to circumvent the laser guide portion; and a laser tube detachably fitted in the laser tube mount member.

Abstract: A phase grating is provided in this length or angle measuring apparatus, which operates by interference. A beam striking the phase grating from a laser is diffracted into .+-.1st order beams at the phase grating. The diffracted .+-.1st order beams are reflected at retroreflecting elements and, diffracted once again at the phase grating, and made to interfere in pairs. The modulations in intensity of the two-beam interferences are converted by detectors into electrical signals that are phase-displaced from one another. The diffraction grating is configured such that at least one partial beam cluster of the zero order of diffraction is involved in the formation of at least one of the two-beam interferences.

Abstract: A Sagnac-type fiber-optic gyroscope having a light source, a fiber coil consisting of an optical fiber, a receiver arrangement which are all connected with gates of a directional coupler, in which the light fed into the fiber coil interferes with the light emerging from the fiber coil in a coupling area and the rate of rotation of the fiber-optic gyroscope is determined from the interference signals. In order to achieve a working point which is situated in or close to the quadrature point, the directional coupler is developed as a 4.times.4 coupler between the arms of which fixed phase relations are provided in the coupling area.

Abstract: A position detecting method for detecting the position of a substrate by use of a grating pattern provided on the substrate includes irradiating the grating pattern with first and second radiation beams having different wavelengths to produce first and second diffraction beams of different wavelengths; and receiving the first and second diffraction beams by use of a sensor to determine the position of the substrate on the basis of the position of incidence of each of the first and second diffraction beams on the sensor.

Abstract: There is disclosed an interference spectrophotometer which collects data while monitoring the position of a movable mirror by providing quadrature control to accurately perform coherent addition of data. The spectrophotometer includes a main interferometer, a control interferometer, a sliding controller controlling movement of the movable mirror, an A/D converter converting analog data obtained by the main interferometer into digital form, a register for holding data obtained by one scan of the movable mirror, a memory for accumulating data obtained by numerous scans of the movable mirror, an up/down counter receiving the output signals from two detectors included in the control interferometer, and a decision part. When the counter's value varies, the counter causes the A/D converter to perform its A/D conversion. Then, the decision part checks the counter's value after the A/D conversion.

Abstract: A method whereby the image produced in a coherence probe microscope is modified by means of a certain specific additive electronic transformation for the purpose of improving the measurement of selected features. The technique improves measurement accuracy on optically complex materials, in particular it improves the accuracy of linewidth measurement on semiconductor linewidths.

Abstract: A dither arrangement or dither spring comprises an outer portion 1 for being secured to a fixed structure, an inner mounting stub 9 for being attached to a sensor such as a laser gyro and a series of three counter-balanced inertias 10 which together have the same inertia as the sensor. The inertias 10 are connected by spoke 6 to flexible pivots 4, to which the mounting stub 9 is also connected by spokes 5.

Abstract: A laser (10) provides an output beam to an interferometer (12). A portion of the output beam is directed by a beamsplitter to a receiver (18) as a reference beam while the remaining portion of the output beam passes through the beamsplitter and impinges on a plane mirror reflective surface (14a) mounted upon or integrally formed with or upon a surface of a body of interest, such as rotary actuator or arm (14). The arm has a fixed center of rotation O and rotates through an angular range indicated by theta-max. Phi is the angle of incidence of the laser beam with the arm in its original position when theta equals zero. .vertline.OC.vertline. and .vertline.CD.vertline. are distances which locate the intersection point between the arm and the laser beam relative to the center of rotation O when theta equals zero. A corner cube (16) is located at a convergence plane and returns all reflected beams back to the plane mirror and hence to the receiver via the interferometer.

Abstract: A relatively simple interferometric method for the absolute testing of plane surfaces is disclosed, along with special apparatus for carrying out the inventive method. Two plane surfaces to be tested (A.sub.6,B.sub.6) are inserted simultaneously into the interferometer's measuring-beam path so that the measuring beam is reflected from each plane surface at two respective and different incident angles (.alpha., .beta.). During successive steps, the plane surfaces (A.sub.6,B.sub.6) are angularly repositioned and shifted so that at least one of the incident angles (.alpha., .beta.) is changed. Interferograms are recorded during each step and analyzed mathematically.

Abstract: A system and method for minimizing polarization-induced phase noise in an interferometric fiber sensor is disclosed.

Abstract: According to the principles of the invention, an improved system and method of accurately measuring the position of an object to high resolution are provided. A read head is positioned adjacent a grating. The read head emits light onto the grating. The light is diffracted into two light beams by the grating. The light beams are reflected back towards the grating, to be diffracted a second time and combined into a single beam. The polarization of the respective light beams is modified before being diffracted the second time. The polarization component of the beam parallel to the diffraction grating grooves is rotated perpendicular to the diffraction grating grooves and the component of the beam perpendicular to the diffraction grating grooves to be rotated parallel to the diffraction grating grooves.

Abstract: An apparatus for reducing the detected optical intensity noise received f an optical interferometric sensor. One embodiment of the device comprises high pass and low pass filtering means and an arithmetic divider device, arranged so as to receive a single signal S.sub.1 and to cancel unwanted intensity noise in signal S.sub.1 prior to the transmittal of the noise free signal S.sub.out to a receiver circuit. A second embodiment of the device further includes an adder and a subtractor to receive two signals S.sub.1 and S.sub.2. The adder and subtractor are cross connected in such a way as to combine the two signals for further processing and also to still permit intensity noise cancellation in the event one of the signals is not available.

Abstract: An apparatus for projecting a mask pattern (MA) on a substrate (W) by means of a projection lens system (PL) is described, which apparatus comprises a device for aligning a substrate alignment mark (P.sub.1 ; P.sub.2) with respect to a mask alignment mark (M.sub.1 ; M.sub.2), the projection lens system (PL) forming part of the alignment device. A correction element (25) is arranged in this system (PL) to compensate for the fact that this system (PL) is not optimized for the wavelength of the alignment beam (b).

Abstract: A characteristic matrix S(j,i) of the system is preformed such that each row j is preformed at a predetermined constant optical path difference. Light from a laser is transmitted through the system at n different laser wavelengths, and a different datum is obtained at each wavelength whereby to obtain a set of n different data. A vector is formed from the n different data, and the characteristic matrix is multiplied by the vector to obtain a correlation vector. The maximum amplitude element of the correlation vector points to the row of a matrix which has the greatest correlation with the obtained data, so that the predetermined optical path difference of that row indicates the phase of the interferometer of the system. In a separate embodiment, the data vector is divided by the characteristic matrix to obtain a second matrix, and the second matrix is used to form an absolute deviation vector.

Abstract: Method and apparatus for determining a backscatter radiation component of a ring laser. Electro-optic apparatus provides to a ring laser resonant cavity, during a first interval of time, a clockwise propagating radiation beam and also provides, during a second interval of time, a counter-clockwise propagating radiation beam. Other electro-optic apparatus measures, during the first interval of time, a magnitude of a backscatter radiation component resulting from the clockwise propagating radiation beam and also measures, during the second interval of time, a magnitude of a backscatter radiation component resulting from the counter-clockwise propagating radiation beam. The measured backscatter magnitudes are input to a processor for calculating a lock-in characteristic of the ring laser.

Abstract: A method for monitoring an alignment of a workpiece with respect to a reference. The method includes a step of attaching to the workpiece a novel optical device comprising a modified corner cube retroreflector. The novel optical device can function such that a specified percentage of incident radiation reflects in accordance with Snell's Law, with a residual reflected beam reflecting retroreflectively. The method further includes a step of directing a radiation beam to the optical device, for generating an interference pattern induced by the Snell's Law and retroreflective beams. The interference pattern provides a measure of the alignment of the workpiece.

Abstract: This invention detects leaks in small, hermetically sealed packages, especially microchips or other packages of electronic circuits. The invention includes a procedure for detecting fine leaks, and a somewhat different procedure for finding gross leaks. To detect gross leaks, one places the package in a chamber, and varies the pressure in the chamber slightly. If the leak is not too big, one wall of the package, such as its lid, initially becomes deformed, but quickly returns to its original position, due to the leak. If the leak is very large, the wall of the package may not move at all. The position of the wall is monitored with an interferometer, preferably an electronic shearography apparatus. The movements of the wall show whether there is a gross leak. In the fine leak test, the package is placed in the chamber and the pressure is changed substantially, thus causing the walls of the package to deform. If there is a fine leak, a deformed wall gradually returns to its initial position.

Abstract: The present optical system provides an all-reflective boresight transfer system. A reflective mechanism receives and reflects energy from an incoming collimated beam to focus it upon a target surface. The target surface absorbs and subsequently re-emits as a longer wavelength most of the energy and also reflects a small portion of the energy such that an exit beam comprised of both the re-emitted and reflected energy is reflected through the reflecting mechanism and re-collimated by the reflecting mechanism. The exit beam has the same direction as the input beam except that it is deviated by 180.degree. and laterally offset from the input beam so that the exit beam may be used as a reference for determining or aligning the line of sight of other optical systems.