Abstract: The present invention is an improved distance measuring interferometer that includes high speed phase modulators and additional phase meters to generate and analyze multiple heterodyne signal pairs with distinct frequencies. Modulation sidebands with large frequency separation are generated by the high speed electro-optic phase modulators, requiring only a single frequency stable laser source and eliminating the need for a first laser to be tuned or stabilized relative to a second laser. The combination of signals produced by the modulated sidebands is separated and processed to give the target distance. The resulting metrology apparatus enables a sensor with submicron accuracy or better over a multi-kilometer ambiguity range.

Abstract: The disclosed method of measuring the thickness of an active layer of an SOI substrate maintains the accuracy of previous methods but can be performed quickly and during processing of the substrate. The method includes reading data from light reflected from the substrate. A range of light wavelengths for analysis is selected, which avoids the problem of nodes, at which interference between light reflected from different surfaces is weakened. The method determines a relationship between wavelength and reflection intensity and determines peak values of the relationship. The wavelengths corresponding to an arbitrary pair of the peak values, and the number of waves between the peak values, are used to calculate the thickness of the active layer. The method includes an error correction procedure that increases measurement accuracy.

Abstract: A vibrometer for probing an object to determine its vibratory signature and a method of probing same. The vibrometer includes a laser for generating a laser beam for probing the object; a detector for detecting reflections from the object; and a two beam input phase-conjugate mirror located so as to receive a portion of the laser beam produced by the laser and a portion of the laser beam reflected from the object, the two input beam phase-conjugate mirror reflecting received diffuse signals from the object back towards the object.

Abstract: A wafer alignment sensor uses a microlens array for sensing the position of an alignment pattern on a semiconductor wafer. Phase interactions between adjacent microlenses are suppressed—or alternatively, enhanced—by inducing a &pgr;/2 optical phase shift on alternate microlenses and by optimizing the optical transmittance profile of the alignment system's projection aperture.

Abstract: Radiation that propagates undeflected through a turbid medium, undergoes a small change in phase velocity due to its wave nature. This change can be measured using a differential phase optical interferometer. Ballistic propagation can be classified into three regimes: For scatterers small compared to the wavelength, the turbid medium acts as a bulk medium; for large scatterers, phase velocity is independent of turbidity; and in the intermediate regime the phase velocity is strongly dependent on scatterer radius. In particular, for scatterers having intermediate size a phase velocity increase and negative dispersion is observed by adding positive dispersion scatterers of higher refractive index. These measurements are made using the phase difference between fundamental and harmonic light and can be used to provide diagnostic information and images of tissue or biological fluids.

Abstract: A method to determine the systematic error of an instrument that measures features of a semiconductor wafer includes the following sequential steps. Collecting sensor data from measurement runs on front and back surfaces of a wafer while the wafer is oriented at different angles to the instrument for each run, yielding a front data set and a back data set for each angle. Then organizing the data in each set into a wafer-fixed coordinate frame. Reflecting all back surface data about a diameter of the wafer creates a reflected back data set. Subtracting the reflected back data from the front data for each wafer angle, and dividing the result by two, yields an averaged wafer shape for each load angle. Adding the reflected back data to the front data and dividing the result by two, yields an instrument signature for each load angle. The symmetric corrector is calculated by taking the average over all instrument signatures at each load angle.

Abstract: Interferometer for measuring a phase difference between a reference beam (37) and an object beam (36′) transformed by an optical element (10), comprising light source means (2), an optical device (3) and detection means (4) in a detection plane (34). The optical device (3) comprises a first light conductor (30) having a first output surface (31) that generates an object beam (36) having a spherical wave front and a second light conductor (32) having a second output surface (33) that generates a reference beam (37) having a spherical wave front, directed onto the detection plane (34), wherein the set-up of the first light conductor (30) and the optical element (10) is such that the transformed object beam (36′) interferes with the reference beam (37) in the detection plane (34).

Abstract: According to the present invention, it is adapted to calculate simultaneously an absolute molecular orientation with an effective second order nonlinear optical constant in an object to be measured without changing a measuring point. Further, in order that a period of time required for measuring an absolute molecular orientation and an effective second order nonlinear optical constant in an object to be measured is reduced, whereby a possibility of damaging the object to be measured can be minimized, measurement is carried out by the use of a single light source in accordance with SHG phase method without shifting the measuring point of the; object to be measured, so that the absolute molecular orientation and the effective second order nonlinear optical constant can be calculated from a fitting curve achieved as a result of fitting the fringe obtained by the above described measurement.

Abstract: The measuring device comprises at least one measuring head having a reference part, which comprises a reference surface against which the moving web is supported. The reference surface comprises a measuring area in the inside of which the property of the web is measured. The reference part is arranged in connection with the measuring head in such a way that below the reference part, there is a substantially open air space. The measuring head comprises means for generating negative pressure in the air space below the reference part, and the reference part comprises holes formed through it, in such a way that the negative pressure generated in the air space affects through the reference part the space between the reference surface and the moving web in such a way that the web is supported against the reference surface substantially over the whole area of the measuring area.

Abstract: A method and system for correcting an angle &thgr;l indicative of a relative angular orientation of a measurement object for the effects of dispersion caused by gas along a measurement path contacting the measurement object, wherein the angle &thgr;l is measured interferometrically at a wavelength &lgr;l, the method and system including: (i) interferometrically measuring the angular orientation at a first wavelength &lgr;q to give a first angle &thgr;q indicative of the angular orientation (ii) interferometrically measuring the angular orientation at a second wavelength &lgr;u not equal to the first wavelength &lgr;q to give a second angle &thgr;u indicative of the angular orientation; and (iii) correcting the angle &thgr;l by an additive factor &Dgr;&thgr;l=−&Ggr;(&thgr;q−&thgr;u), wherein &Ggr;=(nl−1)/(nq−nu) is the reciprocal dispersive power of the gas and nl, nq, and nu are the indices of refraction of the gas at wavelengths &lgr;l, &lgr;q, and &lgr;u, respectively.

Abstract: A scanning microscope allowing fluorescence observation and morphological observation to be simultaneously performed on the same region of interest and permitting both a fluorescence observation image and a morphological observation image to be obtained within a reduced period of time. The scanning microscope includes a device for splitting low-coherence light from a low-coherence light source between a first optical path and a second optical path. A frequency modulator is placed in at least one of the first and second optical paths to produce a frequency difference between light passing through the two optical paths. An objective optical system is placed in the first optical path to apply light to a sample and to collect light from the sample. A scanning device is placed in the first optical path to scan the sample and the light applied by the objective optical system relative to each other in a plane perpendicular to the optical axis. A combining device combines together the first and second optical paths.

Abstract: An optical fiber chromatic dispersion distribution measuring apparatus for measuring the chromatic dispersion distribution of an optical fiber under test comprising two light sources 1, 2 at least one of which can change wavelength thereof, wherein light beams having different wavelengths from each other and emitted from the two light sources are inputted to the optical fiber under test 7 to measure a four-wave mixing light beam generated by interaction between the two light beams by optical time domain reflectometer (OTDR) 9; wherein an optical bandpass filter 8 having a fixed center wavelength is provided at a previous stage of the optical time domain reflectometer (OTDR); and wherein a coherence controller 10 for controlling coherence of at least one of the light beams outputted from the two light sources 1, 2.

Abstract: An on-line measuring system for measuring a thickness of a transferred substrate includes a first image detector, a second image detector, an elevator, and a display device. After the first image detector indicates a vertical variation of a bottom surface of the substrate, the second image detector captures an image of the bottom surface of the substrate. The elevator perpendicularly moves the second image detector with respect to the bottom surface of the glass substrate, depending on the vertical variation of the bottom surface, such that a vertical distance between the bottom surface and the second image detector remains constant. Then, a controller processes the image of the bottom surface to calculate a distance between opposite edges of the bottom surface, thereby obtaining a thickness of the substrate.

Abstract: An improved confocal microscope system is provided which images sections of tissue utilizing heterodyne detection. The system has a synthesized light source for producing a single beam of light of multiple, different wavelengths using multiple laser sources. The beam from the synthesized light source is split into an imaging beam and a reference beam. The phase of the reference beam is then modulated, while confocal optics scan and focus the imaging beam below the surface of the tissue and collect from the tissue returned light of the imaging beam. The returned light of the imaging beam and the modulated reference beam are combined into a return beam, such that they spatially overlap and interact to produce heterodyne components. The return beam is detected by a photodetector which converts the amplitude of the return beam into electrical signals in accordance with the heterodyne components. The signals are demodulated and processed to produce an image of the tissue section on a display.

Abstract: A blood vessel imaging system includes a measuring light source which emits a measuring light beam. An optical heterodyne detection system consists of an optical system which splits the measuring light beam into a first light beam traveling to impinge upon an organism and a second light beam traveling not to impinge upon the organism and combines the second light beam with the first beam emanating from the organism into a combined light beam, a frequency shifter which causes the first and second light beams to have frequencies different from each other, and a beat component detector which detects beat components of the combined light beam. A band-pass filter detects, out of the beat component detection signal output from the beat component detector, off-centered components in a frequency band deviated from the center frequency of the beat component detection signal by a predetermined width.

Abstract: The present invention is a thickness measurement device which allows high-speed, high precision and stable measurement with a simple configuration and with easy maintenance. A coherent light emitted from a light source 31 is transformed to a desired linearly polarized light by a polarizer 32, this linearly polarized light is entered into a test object 33 having double refraction, a normal beam and an abnormal beam are extracted, the extracted beams are entered into a wedge prism 34, and a beam which transmit through the measurement location of the test object 33 and has the phase difference which changes according to the total thickness of the test object 33 and the wedge prism 34 are extracted.

Abstract: In a wafer thickness measuring apparatus and a method thereof, detection values are obtained from a sample piece (for example, a wafer chip) at a plurality of measurement points thereon by first and second detectors for absolute measurement of distances, and at the same time, measurement values of the fluctuations, for relative measurement of distances, are obtained by the optical heterodyne interferometer, and those measurement values are memorized as a plurality of measurement data being related with those measurement values. When measuring the thickness of a wafer, the measurements are performed at measurement points on the wafer which has a front surface and a reverse surface in height lying within the height of the sample piece, on which such a correspondence is obtained, thereby obtaining the detection values of the first and second detectors.

Abstract: Displacement measuring interferometers (DMI) are disclosed for use in conjunction with apparatus for measuring and monitoring the intrinsic optical properties of the gas in the measurement leg of a DMI to compensate for variations in the refractive index of the gas that would otherwise render subsequent displacement calculations less accurate. The DMIs may be used for either linear or angular displacements. Cyclic error compensation, wavelength monitoring and correction, and phase redundancy features are included to further enhance the accuracy with which displacement determinations may be made and are particularly suitable for use in photolithographic applications.

Abstract: An apparatus and method for using an acousto optic scanning laser vibrometer for measuring a dynamic parameter of micro and macro components is disclosed. A coherent source of a laser beam of single wavelength and of stabilized frequency is split into two orthogonal polarized beams. One of the beams strikes the surface of investigation and gets reflected back, and the other polarized beam impinges on the reference surface and gets reflected back. The beam reflected from the surface of investigation and the beam from the reference surface are combined, thereby causing them to interfere. At least one photo detector is positioned at the point of interference. The photo detector output signals are input to a signal processor or phase meter to obtain the dynamic parameter information. Information is provided that is based on the phase shift between the beam striking on the object of investigation and the beam striking the reference surface due to the difference in the optical path.

Abstract: An apparatus and method for performing optical coherence domain reflectometry. The apparatus preferably includes a single output light source to illuminate a sample with a probe beam and to provide a reference beam. The reference beam is routed into a long arm of an interferometer by a polarizing beamsplitter. A reflected beam is collected from the sample. A 90° double pass polarization rotation element located between the light source and the sample renders the polarizations of the probe beam and reflected beam orthogonal. The polarizing beamsplitter routes the reflected beam into a short arm of the interferometer. The interferometer combines the reference beam and the reflected beam such that coherent interference occurs between the beams. The apparatus ensures that all of the reflected beam contributes to the interference, resulting in a high signal to noise ratio.

Abstract: A lithography system for exposing a photosensitive member includes a photosensitive member placement unit, and an interference optical system. The interference optical system produces interference fringes on the photosensitive member so that the interference fringes will be transferred to the photosensitive member. The interference fringes are aligned based on detected light that has passed through the interference optical system.

Abstract: An apparatus is disclosed for generating data representative of a three-dimensional distribution of the light backscattering potential of a transparent or semi-transparent object such as a human eye. The apparatus includes an interferometer, both the reference beam and measurement beam of which are directed toward the object and reflected by respective reference and measurement sites thereof, such that axial motion of the object during measurement affects both beams equally. The measurement beam is raster scanned transversely across each measurement site for which data is obtained. Also, the frequency of one of the beams is shifted by a non-moving frequency shifter, such that the reflected beams combine and are modulated by a heterodyne beat frequency, which is detected when the object path difference is matched with the interferometer path difference.

Abstract: An apparatus for performing high speed scanning of an optical delay and its application for performing optical interferometry, ranging, and imaging, including cross sectional imaging using optical coherence tomography, is disclosed. The apparatus achieves optical delay scanning by using diffractive optical elements in conjunction with imaging optics. In one embodiment a diffraction grating disperses an optical beam into different spectral frequency or wavelength components which are collimated by a lens. A mirror is placed one focal length away from the lens and the alteration of the grating groove density, the grating input angle, the grating output angle, and/or the mirror tilt produce a change in optical group and phase delay. This apparatus permits the optical group and phase delay to be scanned by scanning the angle of the mirror. In other embodiments, this device permits optical delay scanning without the use of moving parts.

Abstract: An apparatus and method for performing optical coherence domain reflectometry. The apparatus preferably includes a single output light source to illuminate a sample with a probe beam and to provide a reference beam. The reference beam is routed into a long arm of an interferometer by a polarizing beamsplitter. A reflected beam is collected from the sample. A 90° double pass polarization rotation element located between the light source and the sample renders the polarizations of the probe beam and reflected beam orthogonal. The polarizing beamsplitter routes the reflected beam into a short arm of the interferometer. The interferometer combines the reference beam and the reflected beam such that coherent interference occurs between the beams. The apparatus ensures that all of the reflected beam contributes to the interference, resulting in a high signal to noise ratio.

Abstract: The invention features interferometry systems and methods that quantify nonlinearities, e.g., cyclic errors, in an interference signal produced by an interferometry system. The systems and methods analyze interference signals for each of multiple Doppler shifts to thereby resolve nonlinearities that may otherwise overlap spectrally with a dominant interference signal, and also, to interpolate the contributions of the nonlinearities to measurements at different Doppler shifts. The time-varying interference signal or the phase extracted from the time-varying interference signal is Fourier transformed and at least some of the nonlinearities are associated with peaks in the square modulus of the Fourier transformed signal (i.e., the power spectrum). The amplitude and phase of the Fourier transform at the frequency of each such peak are used to quantify the associated nonlinearity. The quantified nonlinearities are used to correct optical path length measurements by the system.

Abstract: An apparatus and method for performing optical coherence domain reflectometry. The apparatus preferably includes a single output light source to illuminate a sample with a probe beam and to provide a reference beam. The reference beam is routed into a long arm of an interferometer by a polarizing beamsplitter. A reflected beam is collected from the sample. A 90° double pass polarization rotation element located between the light source and the sample renders the polarizations of the probe beam and reflected beam orthogonal. The polarizing beamsplitter routes the reflected beam into a short arm of the interferometer. The interferometer combines the reference beam and the reflected beam such that coherent interference occurs between the beams. The apparatus ensures that all of the reflected beam contributes to the interference, resulting in a high signal to noise ratio.

Abstract: The invention relates to a process and to a device for measuring the thickness of transparent materials. More particularly, but not exclusively, the invention concerns the thickness measurement of glass materials and, even more precisely, the thickness measurement of flat glass, in particular float glass. According to the invention, a light beam with modulated frequency is focused, two light beams or rays reflected by each of the surfaces of the transparent material are received, interference is created between them, the number of oscillations per modulation period of the interference signal is determined, the path difference (&dgr;) between the two beams and the thickness (e) of the transparent material are deduced and the phase shift (&phgr;) of the said interference signal is determined. This determination of the phase-shift between the two signals each coming from one of the surfaces of the transparent material can then be used to deduce other characteristics of the said material.

Abstract: Described is a method of interferometric measurement of positions and position changes, as well as physical quantities derived therefrom, of a part to be tested using heterodyne interferometry, with a laser being modulated to change the frequency of the radiation emitted by it using a time-variable pulsating injection current in order to generate the heterodyne frequency, and one portion of the emitted radiation is routed via an optical bypass, while the other portion is routed without the optical bypass to the part and, from there, to a measuring receiver. Improved evaluation of the measurement results is achieved with smaller dimensions due to the fact that the signal shape of the injection current has a rising edge that is steep compared to its pulse length and a subsequent plateau.