Abstract: Disclosed herein is a method including: (i) providing a light transmissive sample including nominally parallel internal facets, which are about perpendicular to an external surface of the sample; (ii) providing an optical element having a refractive index about equal to that of the sample and including an external first surface and an external second surface acutely inclined relative thereto; (iii) positioning the second surface of the optical element adjacent to the first surface of the sample; (iv) impinging light beams on the first surface of the optical element, about normally thereto; (v) sensing light beams, which exit out of the sample following passage of the impinging light beams via the optical element, transmission thereof into the sample, reflection once off the internal facets, and exit out of the sample; and (vi) based on the sensed data, computing a deviation from parallelism between the internal facets.

Abstract: A heterogeneous integration detecting method and a heterogeneous integration detecting apparatus are provided. The heterogeneous integration detecting method includes the following. Under the condition of maintaining the same relative distance between an interference objective lens and a sample, the relative posture of the interference objective lens and the sample is continuously adjusted according to the change of an image of the sample in the field of view of the interference objective lens until a first optical axis of the interference objective lens is determined to be substantially perpendicular to the surface of the sample according to the image. The interference objective lens is replaced with an imaging objective lens and the geometric profile of at least one via of the sample is detected. A second optical axis of the imaging objective lens after replacement overlaps with the first optical axis of the interference objective lens before replacement.

Abstract: The present invention relates to a measuring device having a structure for adjusting inclination of an observation surface of a sample with respect to a reference surface which is orthogonal to an optical axis of an objective lens, and the like. The measuring device includes a scanner, arranged on a propagation path of illumination light traveling from a light source toward the sample, configured to change an emission angle of the illumination light, and inclination information of the sample is obtained by associating a signal value of a detection signal for reflected light from the sample and the emission angle of the illumination light, while changing the emission angle of the illumination light by the scanner.

Abstract: A laser interference device includes: a measurement mirror being movable in an X direction; a reference mirror disposed at a position different from a position of the measurement mirror in a Y direction; a beam splitter having a splitting surface that divides a laser beam into a measurement light and a reference light; a first light guide configured to guide the measurement light incident from the beam splitter and emit the measurement light toward the measurement mirror; and a second light guide configured to guide the reference light incident from the beam splitter and emit the reference light toward the reference mirror, in which a first distribution path formed by the first light guide and a second distribution path formed by the second light guide are mutually equal in a mechanical path length and an optical path length.

Abstract: The optical angle sensor comprises a diffraction unit, a light source, a light receiving unit, and a plurality of reflection units. The diffraction unit includes a first diffraction part for generating combined light and a second diffraction part for diffracting a first light and a second light a plurality of times. The plurality of reflection units includes a first reflection unit, a second reflection unit, a third reflection unit that reflects the first light and the second light through the second diffraction part toward the second diffraction part, fourth reflection unit, and fifth reflection unit. The calculating unit, with the rotation of the diffraction unit, calculates the amount of change in the angle based on the change in the interference signal caused by the combined light generated on the light receiving surface.

Abstract: The present invention discloses a real-time normalization apparatus and method of the PGC demodulation in a sinusoidal phase modulation interferometer. An optical setup containing a measuring interferometer and a monitoring interferometer is constructed. An electro-optic phase modulator is placed in the common reference arm of the two interferometers. High-frequency sinusoidal wave modulation and low-frequency triangular wave modulation are applied to the electro-optic phase modulator at the same time. Sinusoidal modulation is used for generating phase carrier, and PGC demodulation is performed to obtain quadrature signals containing the phase information to be measured. Triangular wave modulation makes the quadrature signals change periodically. Ellipse fitting is performed on the Lissajous figure corresponding to the quadrature signals, and real-time normalization of the PGC demodulated quadrature signals is achieved.

Abstract: An illumination apparatus includes a light source, a polarization conversion element configured to convert light from the light source into polarized light having a specific polarization direction and to emit the polarized light to an illumination surface, and a photosensor configured to receive light emitted from a surface different from an incident surface and an exit surface of the polarization conversion element.

Abstract: Provided is a method for angle calibration of a rotary shaft, including: attaching a calibrating angular sensor to a first rotary shaft of an industrial machine including a plurality of rotary shafts and a control unit that controls the rotary shafts based on an angle detected by a controlling angular sensor provided for each rotary shaft, the calibrating angular sensor being more precise than the controlling angular sensor; connecting the calibrating angular sensor in place of the controlling angular sensor of a second rotary shaft; rotating the first rotary shaft; calculating a difference between a first angle of the first rotary shaft detected by the controlling angular sensor and a second angle of the first rotary shaft detected by the calibrating angular sensor; and storing the calculated difference as a calibration value for an angle of rotation of the first rotary shaft.

Abstract: A sensor arrangement comprises at least a first, a second, and a third light sensor. A three-dimensional framework comprises at least a first, a second, and a third connection means which are connected to the at least first, second, and third light sensor, respectively. The first, the second, and the third connection means are configured to align the at least first, second, and third light sensor along a first, second, and third face of a polyhedron-like volume, respectively, such that the sensor arrangement encloses the polyhedron-like volume. The invention also relates to a method for operating the sensor arrangement.

Abstract: Apparatus and methods are described including a line spectrometer that receives a point of light. The line spectrometer includes a first optical element, and a second optical element configured to convert the point of light to a line of light and to direct the line of light toward the first optical element. The first optical element defines first and second surfaces, a distance between the first and second surface varying as a function of distance along the first optical element, the first optical element thereby being configured to generate first and second reflected lines of light that reflect respectively from the first and second surfaces. A detector array receives the first and second lines of light, and generates an interferogram in response thereto. A computer processor determines a spectrum of the point of light, by analyzing the interferogram. Other applications are also described.

Abstract: An image of an object can be synthesized either from the Fourier components of the electric field or from the Fourier components of the intensity distribution. Imaging with a lens is equivalent to assembling the Fourier components of the electric field in the image plane. This invention provides a method and a means for lensless imaging by assembling the Fourier components of the intensity distribution and combining them to form the image with the use of amplitude splitting interferometer. The angular spectrum of the electromagnetic radiation consists of wavefronts propagating at different angles. The amplitude of each wavefront is split and interfered with itself to create sinusoidal fringe patterns having different spatial frequencies. The sinusoidal fringe patterns are combined to form an image of the object. This method applies to coherent and incoherent light. A method of measuring the angular spectrum I(?x,?y) of an object, i.e. the intensity of the wavefront vs angle of incidence.

Abstract: Described are imaging systems that employ diffractive structures as focusing optics optimized to detect visual edges (e.g., slits or bars). The diffractive structures produce edge responses that are relatively insensitive to wavelength, and can thus be used to precisely measure edge position for panchromatic sources over a wide angle of view. Simple image processing can improve measurement precision. Field-angle measurements can be made without the aid of lenses, or the concomitant cost, bulk, and complexity.

Abstract: Spectral interferometric systems and methods to characterize lateral and angular spatial chirp to optimize intensity localization in spatio-temporally focused ultrafast beams are described. Interference between two spatially sheared beams in an interferometer leads to straight fringes if the wavefronts are curved. To produce reference fringes, one arm relative to another is delayed in order to measure fringe rotation in the spatially resolved spectral interferogram. Utilizing Fourier analysis, frequency-resolved divergence is obtained. In another arrangement, one beam relative to the other is spatially flipped, which allows the frequency-dependent beamlet direction (angular spatial chirp) to be measured. Blocking one beam shows the spatial variation of the beamlet position with frequency (i.e., the lateral spatial chirp).

Abstract: The invention relates to an apparatus for determining the angle (?) between two planar workpiece surfaces (1, 2), comprising a laser transmitter (10) for a laser beam (9), a continuously rotating straightening rotor (3), which is arranged between the two workpiece surfaces (1, 2), is axially parallel to the vertex axis (5) of the angle (?) and has an emission direction for the laser beam (9) that is perpendicular to the rotor axis (4), and comprising a receiving device (11) having a receiver for the laser beam (9) reflected on the workpiece surfaces (1, 2) in the emission direction, and an evaluation circuit (18) connected to the receiving device (11). In order to provide advantageous constructive conditions, it is proposed that the laser transmitter (10) comprises a monitor diode (16) and that the monitor diode (16) forms the receiver for the reflected laser beam (9).

Abstract: An image of an object can be synthesized either from the Fourier components of the electric field or from the Fourier components of the intensity distribution. Imaging with a lens is equivalent to assembling the Fourier components of the electric field in the image plane. This invention provides a method and a means for lensless imaging by assembling the Fourier components of the intensity distribution and combining them to form the image with the use of amplitude splitting interferometer. The angular spectrum of the electromagnetic radiation consists of wavefronts propagating at different angles. The amplitude of each wavefront is split and interfered with itself to create sinusoidal fringe patterns having different spatial frequencies. The sinusoidal fringe patterns are combined to form an image of the object. This method applies to coherent and incoherent light.

Abstract: The invention relates to alignment of an interferometer module for use in an exposure tool. An alignment method is provided for aligning an interferometer to the tool while outside of the too. Furthermore, the invention provides a dual interferometer module, an alignment frame use in the alignment method, and an exposure tool provided with first mounting surfaces for cooperative engagement with second mounting surfaces of an interferometer module.

Abstract: A beam brush includes one lens fixed for receiving a laser beam propagating along a first beam axis, a retroreflector positioned for redirecting the laser beam onto a second beam axis through a change in beam path length, and a second lens transmitting the redirected beam. The retroreflector is rotatable about an offset axis and has its angle of rotation controlled for affecting a change in beam path length. The angle of rotation resulting in the path length change is selected for providing a focus or divergence of the reflected beam transmitted through the second lens. Such a system is useful as a Z-axis focusing device operable an X-Y scanner located downstream the modified beam.

Abstract: A chip scale star tracker that captures plane-wave starlight propagating in free space with a wafer-thin angle-sensitive broadband filter-aperture, and directs the light into a waveguide structure for readout. Angular information about the star source is determined from characteristics of the starlight propagating in the waveguide. Certain examples include internal propagation-constant-based baffling to elimination stray light from extreme angles.

Abstract: A novel means of provided velocity control of an interferometer wherein one of the moving components includes the beamsplitter element is introduced herein. Using a moving beamsplitter and coupled flexure mounting allows improved velocity control because the low mass of the beamsplitter enables the systems disclosed herein to respond faster than conventional mirror velocity controlled interferometer instruments with a resultant lower velocity error so as to provide a more stable and lower noise spectra from the analytical instrument. The control of the velocity of the beamsplitter and if desired, one or both of the configured mirrors, reduces the time wasted changing velocity at the ends of each scan. The result is an increase in data collection available in any given experiment time frame. Such desirable arrangements of the present invention thus allow scans to be collected at higher rates, which beneficially increase the ability to monitor rapidly changing systems.

Abstract: A novel means of provided a hybrid flexure mounted moving mirror component in an interferometer is introduced herein. In particular, a linear bearing in combination with a novel flexure mounting having novel tilt and velocity control of the moving optical component is provided. Such an arrangement enables correction of the errors at the mirror itself while also solving the problem of isolating vibration and noise caused by the imperfections in the bearing surfaces used in many conventional interferometers. Using such a coupled flexure mounting of the present invention, in addition to the above benefits, also enhances velocity control because the resultant low mass of the moving mirror assembly enables the systems disclosed herein to respond faster than conventional mirror velocity controlled interferometer instruments and with a lower velocity error so as to provide a more stable and lower noise spectra from the analytical instrument.

Abstract: In an optical distance sensor for measuring object surfaces with high precision and comprising an objective lens for focusing a measuring beam to a measuring spot on the surfaces, measuring errors due to tilt of an object surface can be detected by using a pupil monitor, which senses the radiation intensity distribution of the reflected measuring beam effectively in the pupil of the objective lens to generate a tilt signal, which can be supplied to a correction/calibration table to obtain a correction signal, which is suitable for correcting the primary distance measuring signal of the sensor. Especially for a differential confocal distance sensor having pinholes arranged in front of radiation-sensitive detectors, a further order of correction can be obtained by determining optimum position and diameter of these pinholes.

Abstract: A chip scale star tracker that captures plane-wave starlight propagating in free space with a wafer-thin angle-sensitive broadband filter-aperture, and directs the light into a waveguide structure for readout. Angular information about the star source is determined from characteristics of the starlight propagating in the waveguide. Certain examples include internal propagation-constant-based baffling to elimination stray light from extreme angles.

Abstract: In measuring the displacement of an object using the phase-shifting light interference, since three beam splitters were used for generating the four phase-shifting optical paths, an interferometer was increased in size, whereby the application objects were limited.

Abstract: A method for determining a tilt of an image sensor surface plane in a camera in relation to a lens reference plane of the camera includes sending light onto the image sensor, receiving light reflected from the image sensor, identifying an interference pattern in the reflected light, identifying a feature of the interference pattern, and determining the tilt of the image sensor surface plane based on a position of the feature identified in the interference pattern.

Abstract: Systems and method are disclosed for measuring small angular deflections of a target using weak value amplification. A system includes a beam source, a beam splitter, a target reflecting surface, a photodetector, and a processor. The beam source generates an input beam that is split into first and second beams by the beam splitter. The first and second beams are propagated to the target reflecting surface, at least partially superimposed at the target reflecting surface, and incident to the target reflecting surface normal to the target reflecting surface. The first beam is reflected an additional even number of times during propagation to the photodetector. The second beam is reflected an additional odd number of times during propagation to the photodetector. The first and second beams interfere at the photodetector so as to produce interference patterns. The interference patterns are interpreted to measure angular deflections of the target reflecting surface.

Abstract: A method for configuring an alignment of a plurality of optical segments in a sparse aperture configuration of an optical device includes providing at least one beam of light from at least one light source located on the sparse aperture optical device, directing the at least one beam of light toward at least one segment of the plurality of optical segments, detecting a reflection or transmission of the at least one beam of light off of the at least one segment of the plurality of optical segments, determining a characteristic of the reflected or transmitted light, and based on the characteristic of the reflected or transmitted light, determining an alignment of the at least one segment of the plurality of optical segments.

Abstract: A system that incorporates teachings of the present disclosure may include, for example, an apparatus that includes a processor coupled with a memory where the processor is operable to obtain a first speckled pattern of a first defocused image of a neighborhood of a location on an object, to obtain a second speckled pattern of a second defocused image of the neighborhood, to determine a shift between the first and second speckle patterns, and to calculate slope information of a surface profile at the location based on the determined shift. Other embodiments are disclosed.

Abstract: The power input to the light source of a microscope is varied as necessary to maintain a constant degree of detector saturation as the objective is moved toward a best-focus position. Focus is found by tracking the source's intensity necessary to maintain the detector irradiance at a constant level. The in-focus position is reached when the power input (and correspondingly the intensity of the light emitted by the source) reaches a minimum. The concept can be applied in a similar manner to minimize or eliminate tilt in a sample.

Abstract: A method for aligning a plurality of sub-apertures of a multiple-aperture imaging system including, but not limited to, identifying one sub-aperture to serve as a reference sub-aperture, actuating the reference sub-aperture in a series of piston steps of a known amount, collecting data relating to each image of a plurality of images of a point object, each image corresponding to a respective piston step, compiling the data into a three-dimensional data cube, detecting a plurality of fringes positioned within the three-dimensional data cube, determining the relative location of each sub-aperture of the plurality of sub-apertures based on a location of each fringe of the plurality of fringes within the three-dimensional data cube, and actuating a piston associated with at least one sub-aperture based, at least in part, on the relative location to move the at least one sub-aperture into alignment with another sub-aperture and repeating with each remaining sub-aperture until all sub-apertures are at substantially

Abstract: An interferometer (1) measures a measuring interference beam, while detecting the position of a moving mirror (16) on the basis of detection results obtained from a reference beam detector (25). In the interferometer, a reference beam source (21) is configured by including a light source (21a) composed of a semiconductor laser device. A reference optical system (20) has a collimating optical system (22) for a reference beam, said collimating optical system converting a laser beam outputted from the reference beam source (21) into a collimated beam, and the collimated beam is diagonally inputted to a fixed mirror (15).

Abstract: A surface measurement instrument for obtaining surface characteristic data of a sample surface is described. Relative movement between a reference surface and a sample support is caused to occur while a sensor senses light intensity at intervals along a scan path to provide a series of intensity values representing interference fringes produced by a region of a sample surface during said relative movement and from which series of intensity values surface characteristic data can be derived. The sample support is both translatable and tiltable in at least one direction perpendicular to a scan direction so that the sample support can be both tilted to cause the scan path to be normal to the sample surface region and translated to compensate for translation movement due to the tilting.

Abstract: The present invention may include measuring a first phase distribution across a pupil plane of a portion of illumination reflected from a first overlay target of a semiconductor wafer, wherein the first overlay target is fabricated to have a first intentional overlay, measuring a second phase distribution across the pupil plane of a portion of illumination reflected from a second overlay target, wherein the second overlay target is fabricated to have a second intentional overlay in a direction opposite to and having the same magnitude as the first intentional overlay, determining a first phase tilt associated with a sum of the first and second phase distributions, determining a second phase tilt associated with a difference between the first and second phase distributions, calibrating a set of phase tilt data, and determining a test overlay value associated with the first and second overlay target.

Abstract: A method for determining a tilt of an image sensor surface plane in a camera in relation to a lens reference plane of the camera includes sending light onto the image sensor, receiving light reflected from the image sensor, identifying an interference pattern in the reflected light, identifying a feature of the interference pattern, and determining the tilt of the image sensor surface plane based on a position of the feature identified in the interference pattern.

Abstract: Methods are disclosed wherein the structural health of a civil structure, such as, but not limited to, a bridge or the like is measured by electronic distance measurement (EDM) from a plurality of stable locations to a plurality of cardinal points on the structure in a methodical manner. By measuring the coordinates of the cardinal points, the dynamic and long-term static behavior of the structure provide an indication of the health of the structure. Analysis includes: comparison to a Finite Element Model (FEM); comparison to historical data; and modeling based on linearity, hysteresis, symmetry, creep, damping coefficient, and harmonic analysis.

Abstract: A mirror drive mechanism for a tilting mirror is controlled using feedback from one or more interferometric angular sensors. The wavelength of an optical beam is varied as it is fed into an interferometric angular sensor. The wavelength at which the resulting interference pattern is measured to be at a minimum intensity is determined. This wavelength is used to determine a distance quantity representative of the angular position of the mirror.

Abstract: A method for determining the lateral correction as a function of the substrate topology and/or the geometry of the substrate holder is disclosed. The substrate is placed on a measuring stage traversable in the X coordinate direction and Y coordinate direction, which carries the substrate to be measured. The substrate is supported on at least three support points which define a plane. An apparatus is provided for determining the position of a plurality of positions on the surface of the substrate in the in the X, Y and Z coordinate directions. The substrate is tiltable about an axis parallel to the X/Y plane, to enable the substrate to be measured in a tilted position.

Abstract: A surface measurement instrument for obtaining surface characteristic data of a sample surface is described. Relative movement between a reference surface and a sample support is caused to occur while a sensor senses light intensity at intervals along a scan path to provide a series of intensity values representing interference fringes produced by a region of a sample surface during said relative movement and from which series of intensity values surface characteristic data can be derived. The sample support is both translatable and tiltable in at least one direction perpendicular to a scan direction so that the sample support can be both tilted to cause the scan path to be normal to the sample surface region and translated to compensate for translation movement due to the tilting.

Abstract: Methods are disclosed wherein the structural health of a civil structure, such as, but not limited to, a bridge or the like is measured by electronic distance measurement from a plurality of stable locations to a plurality of cardinal points on the structure in a methodical manner. By measuring the coordinates of the cardinal points, the dynamic and long-term static behavior of the structure provide an indication of the health of the structure. Analysis includes; comparison to a Finite Element Model (FEM), comparison to historical data, linearity, hysteresis, symmetry, creep, damping coefficient, and harmonic terms.

Abstract: The disclosure features multiple degree-of-freedom interferometers (e.g., non-dispersive interferometers) for monitoring linear and angular (e.g., pitch and/or yaw) displacements of a measurement object with compensation for variations in the optical properties of a gas in the interferometer measurement (and/or reference) beam paths. The disclosure also features interferometry systems that feature an array of interferometers (e.g., including one or more multiple degree-of-freedom interferometer), each configured to provide different information about variations in the optical properties of the gas in the system. Multiple degree-of-freedom interferometers are also referred to as multi-axis interferometers.

Abstract: A tilting angle measuring device includes an optical device, a four-quadrant optical detector and a computing unit. By the optical device, a light beam emitted by the coherent light source is processed into a reference beam and a test beam. The four-quadrant optical detector has four photoelectric converting units arranged in an array for respectively receiving the reference and test beams. The computing unit is electrically connected to the four-quadrant optical detector for computing a tilting angle of the object with respect to a predetermined position according to four intensity values of the test beam.

Abstract: A method is disclosed whereby a laser-based spherical coordinate measurement system is dynamically calibrated. A mechanical oscillator, such as, but not limited to, a Foucault pendulum is used to generate periodic motions which can be fitted to Fourier series models. The residuals between the experimental measurements and the model can provide information which can be used to calibrate the instrument. The calibration information is used to augment the ASME B89.4.19-2006 standard to improve sensitivity to cyclic errors and include the servo systems.

Abstract: A position-measuring device is used for measuring the position of an object relative to a tool, the tool having a tool center point. The position-measuring device includes at least two intersected scales displaceable relative to each other in at least one plane of movement, and an assigned optical scanning unit which generates position signals for at least one measuring direction parallel to the plane of movement. Each scale has a neutral pivot, about which a tilt of the respective scale causes no change of the detected position. The scanning optics ensure that the position of the neutral pivots of the two scales correspond. The positioning of the scales relative to the tool center point ensures that the neutral pivots of the two scales and the tool center point lie in a plane which is parallel to the plane of movement.

Abstract: A method of aligning an array of mirrors and computer program product therefor. The method may be used to align mirrors in a sparse aperture telescope system, e.g., a spaced based imaging interferometer. An image projected onto mirrors in an array of mirrors is reflected onto a sensor, where a point spread function (PSF) is collected from a pair of mirrors. A spatial image is extracted from PSF sidebands and a difference (e.g., piston difference) is determined for the pair of mirrors from the spatial image. Tip and tilt are determined for the pair of mirrors from spatial image characteristics.

Abstract: An apparatus for scanning a light beam, the apparatus comprises a mirror configured to reflect an incident light beam, a motor configured to rotate the mirror so change a direction along which the light beam reflected by the mirror travels, a detector configured to detect tilt of a detected region of the mirror with respect to a rotation angle of the mirror, and a processor configured to calculate an amount of tilt of the mirror with respect a direction along a rotation axis of the motor, based on the rotation angle of the mirror and the tilt of the detected region detected by the detector.

Abstract: A first positional information of a wafer stage is measured using an interferometer system such as, for example, a Z interferometer. At the same time, a second positional information of the wafer stage is measured using a surface position measurement system such as, for example, two Z heads. Moving average is applied to a difference between the first positional information and the second positional information for a predetermined measurement time to set a coordinate offset, and the coordinate offset is used to inspect the reliability of output signals of the surface position measurement system. When the output signals are confirmed to be normal, servo control of the wafer stage is performed using a sum of the first positional information and the coordinate offset. According to the servo control by this hybrid method, drive control of the wafer stage which has the stability of the interferometer and the precision of the Z heads becomes possible.

Abstract: An alignment stage includes a first plane mirror which extends in two directions substantially perpendicular to each other in order to measure the position of a stage in the translation direction and the tilt of the stage in the direction of height, a first measurement unit which irradiates the plane mirror with a laser beam and measures the position of the stage in the translation direction by using reflection of the laser beam, and a second measurement unit which irradiates the first plane mirror with a laser beam and measures the position by using reflection of the laser beam at a position vertically spaced apart from the firs measurement unit in order to measure the tilt of the stage.

Abstract: A measuring apparatus and method which is sensitive to rotational but not translational or vibrational movement. The magnitude of an applied rotational force is determined based upon interference patterns created from light reflected from an interferometric prism positioned to rotate in response to an applied rotational force.

Abstract: A Fizeau or other interferometer is used to provide high resolution, in-situ calibration of an external angle measurement system such as widely spaced high stability plane mirror interferometers (HSPMIs)). The calibrated measurement system then measures mechanical tilt during shearing. The tilt data is used to correct the sheared data, preferably before computation of the rotationally invariant (RI) terms. Alternatively, the data may be used to compute the spurious quadratic term and correct after integration.

Abstract: A method of determining an amount of tilt may include projecting at least two coherent wavefronts toward a target surface, the wavefronts reflecting from the target surface to create an interference fringe pattern on a detector, and transmitting a beam toward the target surface, the transmitted beam reflecting from the target surface to form a beam spot on the detector. A fringe pitch indicative of a distance to the target surface may be determined based on the interference fringe pattern. A displacement on the detector of the beam spot, relative to a nominal location of the beam spot when the target surface is at a nominal angle of incidence relative to the beam, may be determined. The amount of tilt of the target surface relative to the nominal angle of incidence, may be determined based on the displacement of the beam spot and the determined fringe pitch.

Abstract: Multidirectional retroreflectors and methods of reflecting light beams from multiple directions are provided. The multidirectional retroreflectors utilize a four-mirror retroreflector with a common virtual reflection point.