Abstract: The present invention relates to a non-contact, non-destructive measuring apparatus that measures thickness profile and refractive index distribution of a single or multiple layers of thin films by means of the principle of reflectometry. According to the present invention, by employing more than one narrow band-pass optical filters and a two-dimensional array of CCD sensors, and by finding an optimal solution for the nonlinear functional relationship between the thickness of said thin film or thin films and the corresponding refractive indexes by using an iterative numerical computation method, said apparatus simultaneously measures local area-wise thickness profile and refractive index distribution among others of said a single layer or multiple layers of thin films on a substrate.

Abstract: A method of performing closed loop correction of phase aberrations, including the steps of directing an incoming light beam into a black fringe wavefront sensor via an adaptive optical device (“AOD”), dividing the incoming light beam into measurement and reference beams, altering the path length of the measurement beam and the location of the black fringe by modulating a ramp voltage of a modulator, combining the measurement and reference beams into a common output beam, detecting the black fringe in the common output beam using detectors mapped to the AOD, storing, as tagged ramp voltages, a corresponding ramp voltage for each detector when it detects black fringe, calculating phase errors based upon the tagged ramp voltages and modulator scaling, calculating adaptive optics correction voltages based upon the phase errors, transmitting and applying the correction voltages to the AOD to correct phase aberrations of the incoming light beam via phase conjugation.

Abstract: An apparatus and method is provided for facilitating ionization of a gas medium of a laser gyroscope. The apparatus and method employ a solid state light emitting device as a start aid for the laser gyroscope. The solid state light emitting device has a wavelength at or below a threshold wavelength based on a work function of a cathode coating material to prompt ionization of a gas medium within the laser gyroscope.

Abstract: The method serves for the interferometric measurement of non-rotationally symmetric wavefront errors on a specimen . The specimen is brought into a number of rotational positions, at least one measurement result being determined in each of the rotational positions and a mathematical evaluation of all measurement results is performed. The measurement results (M1 . . . Mm; N1 . . . Nn) of each of the measurement series (M, N) are determined respectively in mutually equidistant rotational positions of the specimen . The measurement results (M1 . . . Mm, N1 . . . Nn) of each of the at least two measurement series (M, N) are evaluated independently of one another for non-rotationally symmetric wavefront errors (<W>m, <W>n) on the specimen, and a difference is computationally rotated m or n times and the results averaged out. At least one of the wavefront errors (<W>m, <W>n) is corrected with the result (<<W>m-<W>n>m or <<W>m-<W>n>n) averaged in this way.

Abstract: In general, in one aspect, the invention features a method for determining the location of an alignment mark on a stage including measuring a location, x1, of a stage along a first measurement axis using an interferometry system, measuring a location, x2, of the stage along a second measurement axis parallel to the first measurement axis, and determining a location of the alignment mark along a third axis parallel to the first measurement axis based on x1, x2, and a correction term, ?3, calculated from predetermined information including information characterizing imperfections in the interferometry system determined using the interferometry system and the stage.

Abstract: A fiber characterization arrangement utilizes Fourier domain optical coherence tomography (FDOCT) to measure the cross-section of optical fibers, thus providing information sub-surface features, coating thickness/concentricity and stress-induced birefringence under tension. The FDOCT technique can also be used to study microstructured fibers. By making FDOCT measurements on a fiber placed in a cavity, the geometric and optical thickness of the fiber can be simultaneously measured, allowing for the determination of the refractive index of the fiber.

Abstract: A system, circuit and method are disclosed for operating a Ring Laser Gyroscope (RLG) off-mode-peak to avoid exciting undesirable transverse modes. An alternate PLC operating point can be used to bias the optical path length of the RLG to an appropriate side of an ideal integer number of wavelengths, and thus avoid exciting the undesirable transverse modes. Although this alternate PLC operating point is not perfect with respect to establishing an integer number of wavelengths, this operation provides acceptable performance of the RLG's (in particular, short length path RLG's), and acceptable margin can be established relative to variations in the PLC set points involved.

Abstract: An optoelectronic detector system is for generating a plurality of periodic, phase-shifted scanning signals from the scanning of a periodic fringe pattern. The fringe pattern extends in a detection plane with fringe-pattern period P in a fringe-displacement direction. The detector system is made up of a plurality of detector elements, the geometrical shape of the detector elements being selected such that a defined filtering of unwanted harmonics from the scanning signals thereby results. Within one fringe-pattern period P, a total of N detector elements of the same geometrical shape are arranged one immediately after the other in measuring direction x.

Abstract: Disclosed herein is a method and apparatus for simultaneously measuring a displacement and angular variations. The method and apparatus of the present invention allows light radiated from a single light source to be placed along a light axis so as to simultaneously measure a distance (displacement) and angular variations that are different physical quantities, so that the displacement and angular variations of the measuring device of a precision measuring apparatus or machining device of a machine tool moved by a stage can be simultaneously measured without an Abbe error.

Abstract: An optical image measuring apparatus capable of effectively obtaining a direct current component of a heterodyne signal which is composed of background light of interference light is provided.

Abstract: The invention concerns a tandem interferometer for temperature sensing. The low coherence interferometry (LCI) system comprises a polarization-based sensing interferometer comprising a birefringent crystal having a sensor temperature sensitivity and a birefringence dispersion, and a readout interferometer being either a Fizeau interferometer using an optical wedge or a polarization interferometer using a birefringent wedge. In one embodiment of the invention, the birefringent crystal has dispersion properties similar to that of the birefringent wedge or that of the optical wedge of the readout interferometer. The present invention also provides a signal processing method for correcting the dispersion effect and for noise filtering in LCI-based optical sensors of the tandem interferometer arrangement.

Abstract: In general, in a first aspect, the invention features a method for determining the location of an alignment mark on a stage, which includes directing a measurement beam along a path between an interferometer and a mirror, wherein at least the interferometer or the mirror is mounted on the stage, combining the measurement beam with another beam to produce an output beam comprising information about the location of the stage, measuring from the output beam a location, x1, of the stage along a first measurement axis, measuring a location, x2, of the stage along a second measurement axis substantially parallel to the first measurement axis, calculating a correction term, ?3, from predetermined information characterizing surface variations of the mirror for different spatial frequencies, wherein contributions to the correction term from different spatial frequencies are weighted differently, and determining a location of the alignment mark along a third axis parallel to the first measurement axis based on x1, x2,

Abstract: The invention provides a method and a system for measuring a physical quantity by means of a tandem interferometer optical sensor system based on low-coherence interferometry. The system comprises a light system, a sensing interferometer and a polarization readout interferometer. The invention provides a polarization interferometer comprising a single birefringent wedge. The invention also provides for a dispersion-compensated optical sensor system. The invention also provides an interferometer sensitive to temperature that comprises a trajectory in a LiB3O5 crystal with an x-cut orientation.

Abstract: A far-field measurement instrument has multiple imaging lenses cut into a pentagon shape and arranged in geodesic spherical configuration with a common field of view focused on the source of the scattered light to be measured. Aspheric lenses are used to facilitate collimation of large incident angles of scattered light. A measurement module, such as a camera, is used behind each lens. The measurement module may consist of an interferometer or Shack-Hartman wavefront sensor, thereby enabling the measurement of both intensity and phase of the scattered light.

Abstract: A method and system for controlling the temperature of the single mode fiber connectors and single mode, polarization maintaining fiber connectors, which that are used in the semiconductor source spectroscopy systems, is described to stabilize the system against baseline drift. Research and modeling has identified the source of thermally induced shifting to the single mode fiber connectors and single mode, polarization maintaining fiber connectors that are used to assemble the semiconductor source spectroscopy systems.

Abstract: In an embodiment of a ring laser gyroscope, a hollow bandgap fiber is filled with a gas or material that will generate laser beams within the fiber upon being excited by an energy source. A detector coupled to the fiber detects a standing wave pattern within the fiber, wherein changes in the detected standing wave pattern indicates a corresponding change in the orientation of the fiber.

Abstract: A dynamic light scattering measurement apparatus using a phase modulation type interference method includes an optical coupler for dividing light from a low coherent light source, a converging lens for irradiating one of the divided lights to a sample 9, phase modulators for modulating the phase of the other divided lights, a spectrum measurement means for measuring a spectrum of the interference light of the phase-modulated reference light and the scattered light outgoing from the sample, and an analyzing means for measuring the dynamic light scattering of particles of the sample based on the first order spectrum corresponding to the basic frequency of the phase-modulating signal or a higher order spectrum corresponding to a frequency equal to two, three or the like times the basic frequency appearing in the interference light spectrum measured by the spectrum measurement means.

Abstract: An optical system and optical apparatus prevent degradation of the S/N ratio due to switching between OCT and OCM observation modes and attain a high S/N ratio in both the observation modes. The optical system includes a light source 1 and a light-branching member 2 for branching light from the light source 1 into a reference light path and a signal light path. An objective 3 is placed in the signal light path. A light-scanning system 5 scans light in the signal light path with respect to a sample 4 placed in the signal light path. A beam diameter changing optical system 6 changes the beam diameter of light entering or exiting the light-scanning system 5. A light-combining member 7 combines together the reference light path and the signal light path. A light-detecting element 8 detects light combined by the light-combining member 7.

Abstract: An NIR spectroscopy fluid analyzing system using a series of LED's, each having its own preselected center wavelength, as illumination sources. These wavelengths have overlapping spectral widths, such that the measurement covers a broad spectrum. The LED's illuminate the fluid sample sequentially, and subsequently the transmission absorbance through the sample and the reflectance or scattering from the sample is measured for the wavelength range of each LED. The measurements are performed using photodetectors. The concentrations of component parts of the fluid are expressed in the form of a polynomial, which is a function of the measured transmitted and/or reflected intensities, and of empirical coefficients, which are extracted by prior statistical analysis on measured intensities obtained from a large number of test samples having known concentrations of the component. A novel sample chamber, capable of performing optical absorption measurements on a flowing sample of fluid, is described.

Abstract: The polarization angle ?1 of a polarizer (14) is set, and the reflection intensity S1 in a cross Nicol state and the reference reflection intensity Ref1 of a liquid crystal cell (15) are measured. A different polarization angle ?2 is then set, and the reflection intensity S2 in a cross Nicol state and the reference reflection intensity Ref2 of the liquid crystal cell are measured. The rations S1/Ref1, S2/Ref2 of measured intensities and the ratio S1·Ref2/S2·Ref1 is determined in order to cancel the background components of the reference reflection intensities Ref1, Ref2 thus determining the value of cell gap accurately.