Abstract: A system for mapping a three-dimensional structure includes a projecting optical system adapted to project light onto an object, a correction system adapted to compensate the light for at least one aberration in the object, an imaging system adapted to collect light scattered by the object and a wavefront sensor adapted to receive the light collected by the imaging system and to sense a wavefront of the received light. For highly aberrated structures, a number of wavefront measurements are made which are valid over different portions of the structure, and the valid wavefront data is stitched together to yield a characterization of the total structure.

Abstract: A differential curvature sensing device for measuring a wavefront curvature by employing increased spatial sampling for wavefront testing with mid-frequency error recovery. The device includes a sampling sensor having an output beam, an optical element to split said output beam, a lenslet array in the path of each beam to generate corresponding sampling grids, a shearing element for shifting the grid points in horizontal and vertical directions to produce plural sampling grids having plural grid points for use generating a spatial sampling grid having a density for mid-spatial frequency recovery. The displacement of the shifting less than a pitch size of the lenslet array, and a measuring device measuring plural slopes of plural wavefronts at each grid point to obtain a wavefront normal curvature and corresponding twist curvature terms to determine a principal curvature and directions. The sensor is a Shack-Hartman sensor, shearing interferometer sensor and other discrete-point sampling sensors.

Abstract: The embodiments disclosed herein relate to an electrostatic chuck, or an optically structured element or an optical mask that comprise a metal film as well as a transparent cover applied on a substrate. At least two anti-reflective films are inserted between the metal film and the cover that reduce the reflectance of the metal film, as viewed from the surface, to almost zero. As a result, a direct interferometer measurement of the surface structure of the transparent cover is possible. Methods measurement and of use are also disclosed.

Abstract: A wavefront microscope or camera utilizes a wavefront sensor to measure the local intensity and phase gradient of the wavefront and output image maps based on the intensity and phase gradient. A wavefront sensor provides a metal film having patterned structured two dimensional (2D) apertures that convert a phase gradient of a wavefront into a measurable form onto a photodetector array. A computer is used to analyze the data by separating signals projected and recorded on the array from the different apertures, predict a center of each projection, and sum signals for each projection to display the intensity while determining a center position change/offset from the predicted center to display the phase gradient of the wavefront.

Abstract: A measurement apparatus for measuring a surface map comprises an image sensor, an optical system including a reference surface and arranged to form an interferogram of a reflected wavefront from a test surface and that from the reference surface on an image sensing surface of the image sensor and a calculation unit which calculates a surface map of the measurement target based on the interferogram. The calculation unit calculates the surface map of the measurement target by utilizing first data which expresses, by a first coordinate system, data in a state in which a central axis of the test surface is at a first angle to an optical axis of the optical system, and second data which expresses, by a second coordinate system obtained by shifting the first coordinate system, data in a state in which the central axis is at a second angle to the optical axis.

Abstract: A method of wavefront (100) analysis including applying a transform to the wavefront, applying a plurality of different phase changes (110, 112, 114) to the transformed wavefront (108), obtaining a plurality of intensity maps (130, 132, 134) wherein the plurality of different phase changes are applied to region of the transformed wavefront, corresponding to a shape of the light source.

Abstract: A wavefront measuring method includes steps of: obtaining a first transmitted-wavefront from a first image formed by transmitting beam through a substance at a first angle; obtaining a second image formed by transmitting the beam through the substance at a second angle; formulating a mask corresponding to an interference degree of the second image; converting the first transmitted-wavefront to match with a temporary second transmitted-wavefront from the second image; and unwrapping from the second image, the mask, and a converted first transmitted-wavefront to obtain a second transmitted-wavefront by transmitting the beam through the substance at the second angle.

Abstract: A method of manufacturing an optical element having an optical surface of a non-rotationally symmetric shape is described. Measuring light is generated using an interferometer optics, wherein the interferometer optics has at least one diffractive component having a grating. The optical surface is positioned at a first position relative to the diffractive component, wherein first measuring light diffracted at the diffractive component is incident on the optical surface at plural locations thereof, and at least one first interference pattern generated from first measuring light reflected from the optical surface is detected. The optical surface is positioned at a second position relative to the at least one diffractive component, wherein second measuring light diffracted at the diffractive component is incident on the optical surface at plural locations thereof, and at least one second interference pattern generated from second measuring light reflected from the optical surface is detected.

Abstract: Apparatus for determining a range to a coherent light source emitting a coherent light beam, the apparatus including an image sensor and a processor, the processor being coupled with the image sensor, the image sensor including an imaging plane, for capturing an image of the wave front of the coherent light beam, the image including at least one light speckle, wherein the processor identifies the light speckle on the captured image, determines the characteristic diameter of the identified light speckle, and determines the range by squaring the characteristic diameter and dividing the result of the squaring by the wavelength of the coherent light beam and by a proportionality constant.

Abstract: A method of manufacturing an optical component comprising a substrate and a mounting frame with plural contact portions disposed at predetermined distances from each other is provided. The method comprises providing a measuring frame separate from the mounting frame for mounting the substrate, which measuring frame comprises a number of contact portions equal to a number of the contact portions of the mounting frame, wherein respective distances between the contact portions of the measuring frame are substantially equal to the corresponding distances between those of the mounting frame, measuring a shape of the optical surface of the substrate, while the substrate is mounted on the measuring frame, and mounting the substrate on the mounting frame such that the contact portions of the mounting frame are attached to the substrate at regions which are substantially the same as contact regions at which the substrate was attached to the measuring frame.

Abstract: A geometric measurement system is adapted to precisely measure one or more surfaces of objects such as corneas, molds, contact lenses in molds, contact lenses, or other objects in a fixture. The geometric measurement system can employ one or more of three possible methods of measurement: Shack-Hartmann wavefront sensing with wavefront stitching; phase diversity sensing; and white light interferometry.

Abstract: The focus of the collimating lens in the optical train of a Fizeau interferometer is adjusted to change the power of the test beam illuminating the transmission sphere. As a result, the rays can be made sufficiently perpendicular to the reference surface to eliminate the chromatic focus shift and non-common path errors produced by a light source of wavelength different from the design wavelength of the transmission sphere. By making the position of the collimating lens relative to the beam expander adjustable along the optical axis over some small range, illumination sources of various wavelength can be used in the same interferometer.

Abstract: The invention provides a method and apparatus for evaluating the quality of microelectromechanical devices having deformable and deflectable members using resonation techniques. Specifically, product quality characterized in terms of uniformity of the deformable and deflectable elements is inspected with an optical resonance mapping mechanism on a wafer-level.

Abstract: The light wave interferometer apparatus is provided and includes: a luminous flux, which is sent from the light source and divided into two portions by the luminous flux separation and composition unit, are combined with each other again under the condition that the divided luminous fluxes hold wavefront information corresponding to the surface shapes of the aspherical lens to be inspected and the reference aspherical lens by the respectively corresponding basis spherical lenses. Therefore, a wavefront difference of the aspherical lens to be inspected with respect to the reference aspherical lens is made to be interference fringe information and formed on an image pickup plane of the interferometer CCD camera. The basis spherical lenses have the basis spherical surfaces, the curvatures of which are equal to each other.

Abstract: A measuring apparatus provides data relating to the shape of an input radiation wavefront, the wavefront shape being describable at a pre-determined location in an optical system. The apparatus includes an aberration device which provides an aberration to the input radiation wavefront, the shape of which is defined by a filter function that is complex valued and has non-mixed symmetry, and a detector having a radiation sensitive surface capable of detecting the intensity of incident radiation on the surface, the detector being coupled to an output device that provides a measure of the intensity of the incident radiation. The aberration device is configured to act on an input wavefront shape to produce first and second output radiation signals that are detected by the detector and in combination cause the output device to provide data indicating an extent to which the wavefront shape is non-planar.

Abstract: The invention is a means of providing focusing and the use of focal methods to improve the imaging and meteorological performance of an interferometric, non-image forming system for use in metrology and nanoscale imaging.

Abstract: Disclosed herein is an interferometry device and associated method and computerized media for testing optical components including those with high aberrations, comprising: situating an optical component under test between a source of a spherical test wavefront and a spherical reference mirror; propagating a spherical test wavefront, whereby an axial line is defined by a direction of propagation of said wavefront; deriving a substantially complete first-tilt-alignment wavefront metrology of the optical component under test from a plurality of first-tilt-alignment interferograms obtained with the optical component under test held fixed at a first predetermined tilt angle relative to a direction of propagation of said wavefront; and varying an axial displacement between the optical component under test and the spherical reference mirror to obtain each first-tilt-alignment interferogram. By varying the tilt angle, one can also derive a substantially complete surface metrology of the optical component under test.

Abstract: The light beam measurement apparatus comprises a beam splitter that divides a light beam emitted from a light source unit into two luminous fluxes, a semi-transmitting/reflecting surface that reflects part of one of the divided luminous fluxes back in the opposite direction to the direction of incidence as a sample luminous flux, and reflection-type reference light producing means that converts part of the luminous flux transmitted through the semi-transmitting/reflecting surface into a wavefront-shaped reference luminous flux and outputs this reference luminous flux; this light beam measurement apparatus can carry out both wavefront measurement and light beam spot characteristic measurement on a light beam simultaneously.

Abstract: A method for determining the surface topography of an object with various surface properties in white light interferometry first generates a set of interferograms, produced by a phase shift driving mechanism supplied with known inputs, obtained from a single reflective surface at the location of the test piece. The sequence of interferograms from the test piece then is used to calibrate a sequence of inputs to the phase shift driving mechanism to compensate for non-linear characteristics of the phase shifting mechanism. The temporal interferometric signal or its transform at each pixel of a set of subsequently acquired interferograms from a test piece then is compared with signals or their transforms modeled with different properties of the measuring surface. The measured surface properties which generate a best match to the modeling surface properties are selected as the desired signal.

Abstract: A device for measuring a lens, comprising a first interferometer having a first optical axis and carried on a first adjustment base, a lens holder for holding the lens having a first surface having a first lens optical axis and a second surface having a second lens optical axis, and a platen having a sliding rail and carrying the first adjustment base and the lens holder thereon, wherein the lens holder is movable on the sliding rail, wherein each of the first adjustment base and the lens holder has a tetra-axis adjustment mechanism through which a relative positional relationship of the first optical axis of the first interferometer and the first lens optical axis of the first surface of the lens is adjustable.

Abstract: The present invention provides an interferometric method and system to measure the height profile of reflecting objects with respect of a reference surface. The method comprises obtaining an image of the object along a specular reflection axis, wherein the image corresponds to an intensity pattern projected on the object along a projection axis, and wherein the specular reflection axis corresponds to a direction along which a portion of the intensity pattern is specularly reflected by the object. Then the method comprises calculating an object phase using the image and determining the height profile using the object phase and a reference phase associated to the reference surface.

Abstract: A variable transmittance optical element is provided in an imaging optical system of an endoscope, and includes small etalons or multiple microscopic mirror that have an effective part that allows passage of a light beam received at a unit light receiving area that corresponds to an individual pixel, or a plurality of pixels, of an image pickup device that is provided in the imaging optical system of the endoscope. Each of said small etalons or microscopic mirrors have facing surfaces that are arranged so as to be parallel to one another on a transparent substrate; and the transparent substrate and an image pickup surface of the image pickup device are positioned so that each of the small etalons or microscopic mirrors allows passage of the light beam.

Abstract: An interferometer comprises a wavelength-variable light source. A reference light and a measurement light are synthesized, and the synthesized light is split into a plurality of split lights. A certain phase difference is provided between the split lights through phase shifting optical members. A plurality of interference fringe images formed by the phase-shifted split lights are captured at an imaging unit. Biases, amplitudes and the amounts of phase shift of the interference fringes formed by the plurality of split lights are calculated, based on interference fringe intensities of the imaged interference fringes, which are obtained by disposing a calibrating substrate instead of the measuring object varying the wavelength of the emitted light to plural values, and operating the imaging unit to capture a plurality of images of interference fringes obtained by the split lights.

Abstract: A system and method for in-line inspection of specimens such as semiconductor wafers is provided. The system provides scanning of sections of specimens having predetermined standardized characteristics using a diffraction grating that widens and passes nth order (n>0) wave fronts to the specimen surface and a reflective surface for the transmitted light beam. Light energy is transmitted in a narrow swath across the portion of the surface having the standardized features. The wavefronts are combined using a second diffraction grating and passed to a camera system having a desired aspect ratio.

Abstract: An oblique incidence interferometer is provided for applying a light at a certain angle from the normal to a measurement surface of a target to be measured and measuring a light reflected from the target. A beam splitter element and beam synthesizer element splits the light from a light source into a measurement light to be applied to the target and a reference light serving as the measurement reference. It also orthogonalizes the polarization directions of the measurement light reflected from the target and the reference light and synthesizes the lights. A three-way split prism splits the synthesized light into a plurality of split lights. Imaging units are provided to capture a plurality of interference fringe images formed in accordance with the plurality of split lights. A ¼-waveplate is provided on either one of an entry side and an exit side of the three-way split prism. Polarizers are provided on imaging surfaces of the imaging units.

Abstract: Interferometric methods and apparatus by which the map between pixel positions and corresponding part locations are determined in situ. The part under test, which is assumed to be a rigid body, is precisely moved from a base position to at least one other position in one to six degrees of freedom in three-dimensional space. Then, the actual displacements are obtained. The base position is defined as the position with the smallest fringe density. Measurements for the base and all subsequent positions are stored. After having collected at least one measurement for each degree of freedom under consideration, the part coordinates are calculated using the differences of the various phase maps with respect to the base position. The part coordinates are then correlated with the pixel coordinates and stored.

Abstract: A holographic adaptive optic system for correcting the wavefront of a light. A phase correction device with a plurality of pixels in the path of the light. A holographic wavefront sensor in the path providing a pair of reconstruction beams for each phase correction device pixel. The relative intensity of the two beams being proportional to the amount of aberration present in the initial beam. A detector that measures the relative intensity of the pair of reconstructed beams. The detector connected by at least one individual control connector to the relevant pixel in the phase correction device. The individual control connectors controlling the phase correction device based upon the relative intensity between the two reconstruction beams to reduce the wavefront aberration.

Abstract: In general, in one aspect, the invention features an apparatus that includes an interferometer having a main cavity and an auxiliary reference surface, the main cavity including a partially reflective surface defining a primary reference surface and a test surface. The interferometer is configured to direct a primary portion of input electromagnetic radiation to the main cavity and an auxiliary portion of the input electromagnetic radiation to reflect from the auxiliary reference surface, wherein a first portion of the primary portion in the main cavity reflects from the primary reference surface and a second portion of the primary portion in the main cavity passes through the primary reference surface and reflects from the test surface. The interferometer is further configured to direct the electromagnetic radiation reflected from the test surface, the primary reference surface, and the auxiliary reference surface to a multi-element detector to interfere with one another to form an interference pattern.

Abstract: A system and method for measuring interferences are disclosed. The system is based on the concept of a composite interferometer. The sample is measured while a simultaneous compensation of the phase deviation due to the relative displacement of the optical delay component between the measurements at different pixels of the sample is performed. In the application of profilometry, the information of the surface profile of a material is obtained from the phase shift of the interference signal. By using the proposed compensation mechanism, an axial resolution at nanometer scale can be achieved. For the measurement of a thin film, a polarized probe beam is oblique incident on the sample. The system can perform a simultaneous measurement of the refractive index and the thickness of the thin film. From the ratio of the intensities of the interferograms of TE and TM waves as well as the phase shifts of the interferograms, the refractive index and the thickness of the thin film can then be obtained simultaneously.

Abstract: An optical measuring device for measuring curved surfaces of a measured object. The curved surface to be measured may at least partially have the internal or external shape of a conical or cylindrical surface or of a saddle surface. The measuring device has a system of optical elements which includes at least one lens system and a first deflection optics. The lens system and the first deflection optics are positioned so that a first part of the light beams incident on the lens system is directed perpendicularly onto the curved surfaces of the measured object via the first deflection optics, while a second part of the light beams incident on the lens system is directed onto a reference object. Simultaneous measurement of locations of the measured object which are difficult to access and a reference object is thus made possible.

Abstract: A surface measurement instrument (1) for obtaining surface characteristic data of a sample surface (13) is described. Relative movement between a reference surface (11) and a sample support (15) is caused to occur while a sensor (16) senses light intensity at intervals along a scan path (SP) to provide a series of intensity values representing interference fringes produced by a region of a sample surface (13) during said relative movement and from which series of intensity values surface characteristic data can be derived. The sample support (15) is both translatable and tiltable in at least one direction perpendicular to a scan direction so that the sample support (15) can be both tilted to cause the scan path (SP) to be normal to the sample surface region and translated to compensate for translation movement due to the tilting.

Abstract: A method for measuring a contour variation of a measuring area on an object. The method includes the steps of: irradiating the measuring area with a light beam, wherein reflection or transmission of the beam occurs; splitting the transmitted or reflected beam; combining the split beams with each other and observing a fringe pattern representing a differential phase between the split beams; varying the phase of the split beams relative to each other, such that the differential phase is kept within the range of 2 pi; calculating an optical path length difference from the differential phase; and relating the optical path length difference to the contour variation of the object.

Abstract: A surface profile measuring method using a broad bandwidth light source illuminating a sample surface and a reference surface through a splitter is provided. By changing a distance between the sample surface and the reference surface with a constant step, an interference diagram with a waveform composed of interference data points depicting a relationship of surface height versus illumination intensity is generated. In the beginning, a first data point with greatest illumination intensity is selected from the interference data points on the waveform. Then, a second data point is selected from the data points on the waveform within a predetermined range centered at the first data point to have the waveform showing best quality of symmetry. Then, a peak of a fringe defined by the second data point and its neighboring data points is estimated by using phase compensating approach.

Abstract: A phase shifting imaging module in a handheld imager is provided. The phase shifting imaging module includes a first beam splitter configured to split an image radiation beam into first and second image radiation beams. It also includes a first prism configured to align the first and second image radiation beams, and a second beam splitter configured to split the first and second image radiation beams into four image radiation beams. A second prism aligns the four image radiation beams. A phase mask introduces phase retardation between the four image radiation beams, resulting in four phase shifted image radiation beams. A pixilated sensor generates image data based upon each of the four phase shifted image radiation beams.

Abstract: A tissue imaging system (200) for examining the medical condition of tissue (290) has an illumination optical system (205), which comprises a light source (220), having one or more light emitters, beam shaping optics, and polarizing optics. An optical beamsplitter (260) directs illumination light to an imaging sub-system, containing a spatial light modulator array (300). An objective lens (325) images illumination light from the spatial light modulator array to the tissue. An optical detection system (210) images the spatial light modulator to an optical detector array. A controller (360) drives the spatial light modulator to provide time variable arrangements of on-state pixels. The objective lens operates in a nominally telecentric manner relative to both the spatial light modulator and the tissue. The polarizing optics are independently and iteratively rotated to define variable polarization states relative to the tissue.

Abstract: Multiwavelength interferometric images have the phase and/or frequency of the illuminating light corrected by statistically analyzing the data, and adjusting the phase and/or frequency until a statistical measure reaches a criterion.

Abstract: A free-space adaptive optical laser communication system having signal transmission and reception channels at all terminals in the communication system, wherein wavefront sensing (WFS) and wavefront correction mechanisms are employed along signal transmission and reception channels of all terminals in the communication system (i.e. adaptive optics) to improve the condition of the laser beam at the receiver (i.e. reduce the size of the spot a the detector plane). in the illustrative embodiment, the WFS mechanisms employ a novel WFS control process, in which active updating of reference positions and subaperture locations on the wavefront sensor. These WFS mechanism can be used in diverse application environments, including but not limited to FSO laser communication systems.

Abstract: Disclosed is a system including: (i) an interferometer configured to direct test electromagnetic radiation to a test surface and reference electromagnetic radiation to a reference surface and subsequently combine the electromagnetic radiation to form an interference pattern, the electromagnetic radiation being derived from a common source; (ii) a multi-element detector; and (iii) one or more optics configured to image the interference pattern onto the detector so that different elements of the detector correspond to different illumination angles of the test surface by the test electromagnetic radiation.

Abstract: The present invention is directed to a system and method for using a spatial light modulator (SLM) to perform a null test of an (aspheric) optical surface. In an embodiment, such a system includes an interferometer, an optical element, and an SLM. The interferometer provides electromagnetic radiation. The optical element conditions the electromagnetic radiation to provide a first beam of radiation and a second beam of radiation. The SLM shapes a wavefront of the first beam of radiation resulting in a shaped wavefront corresponding to an optical surface. The shaped wavefront is incident on and conditioned by the optical surface. The shape of the optical surface is analyzed based on a fringe pattern resulting from interference between the shaped wavefront mapped by the optical surface and the second beam of radiation. The system may also include an optical design module that converts a null corrector design corresponding to the optical surface into instructions for the SLM.

Abstract: An exposure apparatus, which equipped with a projection optical system that is configured to project a pattern of an original onto a substrate, includes an interferometer configured to measure a wavefront in a first direction and a wavefront in a second direction of light passed through the projection optical system; a focus detecting unit configured to detect focus positions in the first and second directions of the projection optical system; and a calculating unit configured to calculate wavefront aberration of the projection optical system on the basis of the measurement result of the interferometer and the detection result of the focus detecting unit.

Abstract: A method and apparatus for characterizing an object with a wavefront from the object is disclosed. In one embodiment, the apparatus includes: a reticle positioned in a path of the wavefront, the reticle comprising two superimposed linear grating patterns; at least one light detector positioned relative to the reticle to receive a self-image diffraction pattern of the reticle produced by the wavefront; and at least one processor receiving signals from the light detector representative of the self-image diffraction pattern and deriving derivatives associated therewith, the processor using the derivatives to characterize said object.

Abstract: An off axis paraboloid mirror is used to provide object illumination in an interferometric imaging system. The light from an object illumination light source diverges from a point apart from the focus point of the paraboloid, proceeds to the parabolic mirror surface, and is reflected as a nearly parallel beam to illuminate the object.

Abstract: A method of calibrating an interferometer apparatus uses a calibrating element having a plurality of structures comprising at least one of projections and indentations formed on a surface of the calibrating element at predetermined positions to generate interference fringes in the interferometer apparatus to be calibrated.

Abstract: A free-space adaptive optical laser communication system having signal transmission and reception channels at all terminals in the communication system, wherein wavefront sensing and wavefront correction mechanisms are employed along signal transmission and reception channels of all terminals in the communication system (i.e. adaptive optics) to improve the condition of the laser beam at the receiver (i.e. reduce the size of the spot the detector plane). Speckle-to-receiver-aperture tracking mechanisms are employed in the transmission channel of the communication system and laser beam speckle tracking mechanism in the reception channels thereof, so as to achieve a first level of optical signal intensity stabilization at signal detector of each receiving channel.

Abstract: Apparatus for optical inspection of a sample includes a radiation source, adapted to irradiate a spot on the sample with coherent radiation, and collection optics, adapted to collect the radiation scattered from the spot so as to form a beam of scattered radiation. A diffractive optical element (DOE) is positioned to intercept the beam of scattered radiation and is adapted to deflect a first portion of the beam by a predetermined offset relative to a second portion of the beam, and then to optically combine the first portion with the second portion to generate a product beam. A detector is positioned to receive the product beam and to generate a signal responsive thereto, which is processed by a signal processor so as to determine an autocorrelation value of the product beam.

Abstract: An interferometric method for determining a height profile of regions of the surface area of an object or of several objects, wherein the regions are substantially in different planes, is presented. The optical path of at least one portion of intensity coming from one of the regions is modified while obtaining at least one image, wherein each image contains the portion of intensity and corresponds to an intensity pattern projected on the regions. An object phase associated with the regions is established using the obtained image(s) and a height profile of the regions is determined using the object phase and a reference phase. An optical assembly is used for directing along a common detection axis an intensity coming from said regions that would be otherwise out of sight.

Abstract: An apparatus and corresponding method for coherent hybrid electromagnetic field imaging of a target, where an energy source is used to generate a propagating electromagnetic beam, an electromagnetic beam splitting means to split the beam into two or more coherently matched beams of about equal amplitude, and where the spatial and temporal self-coherence between each two or more coherently matched beams is preserved. Two or more differential modulation means are employed to modulate each two or more coherently matched beams with a time-varying polarization, frequency, phase, and amplitude signal. An electromagnetic beam combining means is used to coherently combine said two or more coherently matched beams into a coherent electromagnetic beam. One or more electromagnetic beam controlling means are used for collimating, guiding, or focusing the coherent electromagnetic beam. One or more apertures are used for transmitting and receiving the coherent electromagnetic beam to and from the target.

Abstract: In general, in a first aspect, the invention features apparatus that include an interferometer having a main cavity and an auxiliary reference surface, the main cavity including a primary reference surface and a test surface. The interferometer is configured to direct a primary portion of input electromagnetic radiation to the main cavity and an auxiliary portion of the input electromagnetic radiation to reflect from the auxiliary reference surface, wherein a first portion of the primary portion in the main cavity reflects from the primary reference surface and a second portion of the primary portion in the main cavity reflects from the test surface. The interferometer is further configured to direct the electromagnetic radiation reflected from the test surface, the primary reference surface, and the auxiliary reference to a multi-element detector to interfere with one another to form an interference pattern.

Abstract: The invention relates to an interferometric method for measuring a height of a first region on a first surface, the first surface having first areas having first optical properties and second areas having second optical properties, the method comprising the steps of generating of first and second coherent light beams, reflecting at least the first coherent light beam from the first region into a first return beam and reflecting the second coherent light beam from a second region into a second return beam, measuring at least a first reflectivity of the first region, determining a topography-dependent phase shift of the first and second return beams for the height measurement based on the first reflectivity.

Abstract: A wavefront interferometry system including: a wavefront interferometer that during operation combines a reference beam from a reference object and a measurement beam from a measurement object to generate a combined beam; and a processor system programmed to processes the combined beam to concurrently generate therefrom a control signal and information about the difference in wavefront profiles of the reference and measurement objects, wherein the control signal controls a system parameter so as to maintain an optical path length difference between a spot on the reference object and a corresponding spot on the measurement object at a constant value mod 2?.