Abstract: Systems configured to generate output corresponding to defects on a specimen and systems configured to generate phase information about defects on a specimen are provided. One system includes an optical subsystem that is configured to create interference between a test beam and a reference beam. The test beam and the reference beam are reflected from the specimen. The system also includes a detector that is configured to generate output representative of the interference between the test and reference beams. The interference increases contrast between the output corresponding to the defects and output corresponding to non-defective portions of the specimen.

Abstract: Methods include simultaneously diffracting a beam in a first direction and a second direction orthogonal to the first direction to form a once-diffracted beam, where the beam comprises a wavefront shaped by a test object, simultaneously diffracting the once-diffracted beam in orthogonal directions to form a twice-diffracted beam, overlapping at least two orders of the twice-diffracted beam in each direction to form an interference pattern at a detector, the interference pattern being formed by multiple copies of the wavefront laterally sheared in the first direction and multiple copies of the wavefront laterally sheared in the second direction; and determining information about the wavefront based on the interference pattern.

Abstract: An imaging system. Implementations of imaging systems may include a laser light source, at least one imaging detector coupled to the laser light source, a shearing interferometer coupled to at least one imaging detector, and a timing system coupled to the at least one imaging detector and the laser light source. A ranging detector may be coupled to the laser light source and the timing system, and at least on sensitivity modulator may be coupled with the at least one imaging detector and with the timing system.

Abstract: A wavefront-aberration-measuring device measures wavefront aberration of a to-be-tested optical system and includes a diffraction grating that splits light transmitted through the optical system, a detecting unit that detects interference fringes produced by beams of the split light, an arithmetic unit that calculates the wavefront aberration from the detected interference fringes, an image-side mask insertable into and retractable from an image plane of the optical system, and an illuminating unit that incoherently illuminates the image-side mask. The image-side mask has an aperture with a diameter larger than ?/2NA, where ? denotes a wavelength of the illuminating unit and NA denotes a numerical aperture of the to-be-tested optical system. The arithmetic unit calculates the wavefront aberration of the optical system from the interference fringes detected with the image-side mask being retracted from the image plane and the interference fringes detected with the image-side mask being in the image plane.

Abstract: An interferometric tracking device is disclosed. A first grating is optically coupled to a second grading such that the second grating is rotationally offset from the first grating. Imaging optics are adapted to image light passing through the first and second gratings onto a focal plane array. A plurality of wedge plates are optically disposed between the imaging optics and the second grating, such that the wedge plates generate a plurality of spots on the FPA when light from a point source is incident upon the first grating.

Abstract: A phase shift amount measurement apparatus able to further correctly measure a phase shift amount of a phase shifter, wherein a laterally offset interference image of a phase shift mask is formed by a shearing interferometer, the interference image is captured by a two-dimensional imaging device, an output signal output from each light receiving element of the two-dimensional imaging device is supplied to a signal processing device, the phase shift amount is calculated for each light receiving element, the light receiving area of the light receiving element is very small, therefore the phase shift amount of any light receiving element outputting a peculiar phase amount due to incidence of diffraction light or multi-reflection light is excluded and the phase shift amount is determined based on the phase shift amount found from output signals of the remaining light receiving elements.

Abstract: A method and device realize shallow gratings-based planar beam splitter/combiner. Non-trivial phase shifts between different ports of resulting interferometers are used to acquire full-field phase measurements. The non-trivial phase shifts between different ports of the planar beam splitter/combiner can be adjusted by simply shearing one grating with respect to the second grating. The two shallow diffraction gratings are harmonically-related and can be recorded on a single substrate for compact interferometric based schemes. During the recording process, the two gratings are aligned such that the grating planes and the grating vectors are parallel to that of each other. The relative phase of the recording beams controls the shearing between the recorded harmonically-related shallow phase gratings. The relative shearing of the two gratings defines the non-trivial phase shift between different ports of the compact planar beam splitter/combiner.

Abstract: A device for focusing a laser light beam includes an emission source of a laser light beam along an optical emission path, first focusing means of the laser light beam in a focusing point (F) located at a focusing distance (D), means for adjusting the position of the focusing point (F) relative to the device, and means for detecting the focusing distance (D) active in feedback on the adjustment means, wherein the detection means detects a parameter characteristic of the light beam leaving the first focusing means and representative of the focusing distance (D). The characteristic parameter is the wavefront radius of curvature of the light beam leaving the first focusing means.

Abstract: Apparatus and techniques for using an optical shearing interferometry to obtain full field mapping of in-plane and out-of-plane displacement field gradients of a sample surface of a sample.

Abstract: An embodiment of a symmetry forming device for an alignment system can include an interferometer, a compensator, and an analyzer. The interferometer can be configured to receive a light beam, where the light beam can be produced from a light source or from combining beams from a plurality of light sources. Further, the interferometer can be configured to split the light beam into two beams, rotate one beam 180 degrees with respect to the other beam about an axis of rotation, and recombine the two beams to form a recombined beam. The compensator can be configured to adjust a path length of either the combined or the recombined beam in first and second polarization directions to form an adjusted light beam. The analyzer can be configured to pass a polarization direction or an amplitude and phase profile of either the recombined or adjusted light beam, where the recombined or adjusted light beam is directed onto a substrate.

Abstract: Optical scattering disk, use and wavefront measuring apparatus. The optical scattering disk includes a transparent substrate (1) and a light scattering layer (2) adjoining a surface of the substrate and having light-scattering-active particles (3). The light scattering layer has an embedding medium (4) which is optically denser than air and directly adjoins the facing surface of the substrate without intervening air gaps and by which the light-scattering-active particles are surrounded. Such optical scattering disks may be used, e.g., in apparatuses for wavefront measurement of high-aperture microlithography projection objectives employing lateral shearing interferometry.

Abstract: In certain aspects, the invention features interferometry systems that include an input assembly positioned to receive a beam emitted from a light source comprising a first component beam and a second component beam, the input assembly being configured to change a dimension of one of the component beams relative to the dimension of the other component beam, an interferometer positioned to receive the component beams propagating from the input assembly, the interferometer being configured to direct the component beams along different paths and to produce an output beam by directing the component beams along a common path, wherein the output beam comprises information about an optical path difference between the different component beam paths, and an output assembly positioned in the path of the output beam and configured to change a dimension of the component beam that contacts the measurement object.

Abstract: A wavefront measurement system includes a source of electromagnetic radiation. An illumination system delivers the electromagnetic radiation to an object plane. A source of a diffraction pattern is in the object plane. A projection optical system projects the diffraction pattern onto an image plane, which includes a mechanism (e.g., a shearing grating) to introduce the lateral shear. A detector is located optically conjugate with the pupil of the projection optical system, and receives an instant fringe pattern, resulting from the interference between sheared wavefronts, from the image plane. The diffraction pattern is dynamically scanned across a pupil of the projection optical system, and the resulting time-integrated interferogram obtained from the detector is used to measure the wavefront aberration across the entire pupil.

Abstract: Disclosed is a method of analyzing an interference fringe, with which method the optical characteristics of an optical system to be examined can be analyzed very precisely. In one preferred form of the invention, the analyzing method includes a step of detecting information related to a first interference fringe produced by interference of two light fluxes, a step of detecting information related to a second interference fringe produced while changing a phase of one of the two light fluxes by ? as multiplied by an odd number (e.g., 1?, 3?, . . . ), and a step of detecting averaged information of phase information of the two interference fringes, on the basis of the detected information of the first and second interference fringes and by use of Fourier transform.

Abstract: A method and device for obtaining a sample with three-dimensional microscopy, in particular a thick biological sample and the fluorescence field emitted by the sample. One embodiment includes obtaining interferometric signals of a specimen, obtaining fluorescence signals emanating from the specimen, recording these signals, and processing these signals so as to reconstruct three-dimensional images of the specimen and of the field of fluorescence emitted by the specimen at a given time.

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: The phase spectrum of an ultrashort pulse is measured based on two-dimensional spectral shearing interferometry with zero delay. The measurement is performed utilizing an optical source pulse from which is extracted a short pulse and from which a chirped component is generated. The chirped component is split into first and second chirped pulses. The first and second pulses are then mixed with the short pulse in a nonlinear medium to produce up-converted and spectrally sheared copies of the first and second chirped pulses, which are measured in a spectrometer. A plurality of path lengths for the first second chirped pulses is provided to shift the relative phases of the first and second chirped pulses for additional measurements. The apparatus and methods are uniquely suited for characterizing single-cycle pulses.

Abstract: An apparatus including an image sensor is disclosed. The apparatus includes a polarization filter, an image sensor, and a processor connected to the image sensor. The polarization filter is adapted to filter out light polarized in a first direction from a first scene. The image sensor is adapted to capture the filtered light, and the image sensor includes support circuits to convert the captured filtered light to image data. The processor is adapted to process the image data to detect features of the first scene. The polarization filter filters out noise component of the image, thus increasing contrast. In another embodiment, a mosaic polarization filter is used to capture a scene in a first image including light from the scene having first polarity and to capture the scene in a second image including light from the scene having first polarity. The two images can be analyzed to determine various characteristics of the scene.

Abstract: A vibration detection device includes: a light source emitting a laser beam; an interferometer including a first vibrating body and a second vibrating body both capable of reflecting the laser beam, the interferometer splitting the laser beam into beams traveling along first to third optical paths, and the interferometer causing interference between a first reflected beam reflected by the first vibrating body in the first optical path and a reference beam passing through the third optical path to form a first interference pattern, and causing interference between a second reflected beam reflected by the second vibrating body in the second optical path and the reference beam to form a second interference pattern; and a detection means quantizing the vibrations of the first and second vibrating bodies on the basis of the formed first and second interference patterns to detect the vibrations.

Abstract: Systems and methods are provided or use with a light source which generates a light beam. These systems may include a detector which detects light beam information and which determines whether multiple modes are present in the light beam so that the light source may be adjusted. These systems may further include a beam splitting device, such as an optical wedge, to provide two sample beams that intersect to provide a fringe pattern. The detector may then detect this fringe pattern and compute a visibility value that may be used to determine whether multiple modes are present.

Abstract: A device for testing a test object in particular a tire (10) by means of a non-destructive measuring method is provided with at least one measuring head (20) by which the test object (10) can be scanned to produce a measurement result. The device is also provided with a positioning means (30) by which the measuring head (20) can be moved between a park position (I) and a measuring position (II). The device is also provided with a pressure chamber in which the test object (10) can be subjected to a prescribed pressure. The device is further provided with a sub-frame (60) on which the test object (10) can be mounted during the test. The sub-frame (60) is supported on a first bearing element (61) by means of which the transmission of vibrations from a base (70) to the sub-frame (60) can be reduced.

Abstract: Techniques and systems for using optical interferometers to obtain full-field optical measurements of surfaces, such as surfaces of flat panels, patterned surfaces of wafers and substrates. Applications of various shearing interferometers for measuring surfaces are described.

Abstract: A measuring apparatus for irradiating measuring light and for measuring optical performance of a target optical system includes a barrel for housing the target optical system, the barrel being rotatable around an optical axis of the target optical system, and an illumination optical system for introducing the measuring light into the barrel, the illumination optical system being movable along a direction perpendicular to the optical axis of the target optical system. The measuring apparatus controls an illumination area of the measuring light in the target optical system using a polar coordinate determined by a rotational angle of the barrel and a moving amount of the illumination optical system.

Abstract: An improved, adaptive optics control system is disclosed. The system comprises a wavefront corrector, a wavefront sensor, a wavefront reconstructor and a wavefront controller. The wavefront corrector has a surface controlled by a plurality of actuators. The wavefront slope sensor has a subaperture separation mechanism for defining a plurality of subapertures through which the distorted wavefront can pass, each subaperture corresponding to an actuator of the wavefront corrector. The wavefront slope sensor produces a wavefront sensor output signal for each subaperture indicative of the distortion of the wavefront. The wavefront reconstructor is adapted to receive the wavefront sensor output signals and calculate corresponding phase estimates based thereon, each phase estimate having a signal-to-noise ratio. The wavefront reconstructor generates a plurality of correction signals to be applied to each of the actuators of the wavefront corrector, each correction signal having a bandwidth.

Abstract: A phase measuring apparatus for measuring phase characteristics of a film applied onto an object to be measured includes a shearing interference system for providing incident light onto the object or light reflected on the object with shearing interference, a detector for detecting shearing interference information, and a computing unit for calculating the phase characteristics of the film based on the shearing interference information.

Abstract: A technique for optical navigation involves summing intensity values from a photodetector array on a per-column and a per-row basis for both reference image data and sample image data and then performing separate one-dimensional cross-correlations on the per-column sums and on the per-row sums to separately determine displacement in the x and y directions, respectively.

Abstract: A method and an apparatus for determining the influencing of the state of polarization of optical radiation by an optical system under test, wherein radiation with a defined entrance state of polarization is directed onto the optical system, the exit-side state of polarization is measured, and the influencing of the state of polarization is determined by the optical system with the aid of evaluation of the exit state of polarization with reference to the entrance state of polarization. An analyser arrangement which can be used for this purpose is also disclosed. The method and the apparatus are used, e.g., to determine the influencing of the state of polarization of optical radiation by an optical imaging system of prescribable aperture, the determination being performed in a pupil-resolved fashion.

Abstract: Beam shearing apparatus for introducing a lateral shear between the components of a light beam. The apparatus is an optical assembly having a polarizing interface and input and output facets and two reflecting surfaces one of which is arranged at an angle generally opposite the input facet and the other of which is arranged at an angle generally opposite the output facet.

Abstract: A measuring method for measuring a wave front of light, which has passed through a target optical system. The method includes the steps of dividing the light that passes the target optical system into a first wave front and a second wave front made by offsetting the first wave front by a predetermined amount in a predetermined direction, obtaining information concerning an interference fringe using shearing interference with divided light, calculating a differential wave front between the first wave front and the second wave front by using the information concerning the interference fringe obtained in the obtaining step, and correcting the differential wave front based on the predetermined amount and a wave number in the predetermined direction.

Abstract: A projection exposure apparatus includes an exposure light source, an illumination system for illuminating a pattern, formed on a first object, with light from the exposure light source and passing through the illumination system, a projection optical system for projecting a pattern, as illuminated with the light, onto a second object for exposure of the same with the pattern, and an interferometer for use in measurement of an optical characteristic of the projection optical system, wherein the interferometer is operable to perform the measurement by use of light from the exposure light source.

Abstract: In a method for manufacturing an optical imaging system, wavefront aberrations caused by an optical imaging system are determined before and after transporting the optical imaging system. At least some of the aberration parameters which are determined in the preceding determination are used as a given precondition for determining aberration parameters in the subsequent determination. This results in a hybrid method, in which the strength of at least two measurement methods are used in a combined form, and specific weaknesses of any one method are avoided.

Abstract: An interferometry system includes an interferometer to split an input beam into a measurement beam and at least one other beam. The interferometer directs the measurement beam along a measurement path that includes at least two passes to a measurement object, and overlaps the measurement beam with the other beam after the measurement beam completes the at least two passes. The path of the measurement beam is sheared during the first and second passes when the measurement object moves along a direction orthogonal to a portion of the measurement path that contacts the measurement object. The interferometry system includes optics to redirect the measurement beam after the first pass and before the second pass so that shear imparted during the second pass cancels shear imparted during the first pass.

Abstract: Described is an anomaly detector apparatus 10 for detecting an anomaly in a substrate, e.g., a tire comprising: a source of coherent light 20 to shine the light 27 directly onto the tire surface 24 and the light being reflected 32 from the tire; a stressing apparatus 12, which is juxtaposed to the tire and which, can optionally stress the tire; a reflected light receiving apparatus 40 for receiving the light 32 reflected directly from the tire surface 24 whether the tire is in a stressed or unstressed condition; a comparator 44 which views and compares images of reflected light from the reflected light receiving apparatus 40 when the tire is stressed or unstressed thereby ascertaining an anomaly in the tire and generates an output from the comparison; and a display apparatus 46 electronically connected to the comparator for displaying the output from the comparator.

Abstract: Optical instruments having, inter alia, optics to process wavelengths of electromagnetic radiation to produce an interferogram. The instruments include at least one optical path and optical elements positioned along this path for splitting and recombining the wavelengths which interfere with each other to produce a plurality of different fringes of different wavelengths. In one group, the optics include matched gratings which are positioned along the optical path outside of the interferometer optics to produce first and second sets of spectrally dispersed beams. The interferometer optics also includes a beam splitter and first and second mirrors. The gratings may be positioned in a variety of locations along the optical path. In another group, the optics include a beam splitter having a plurality of surfaces, wherein each of the surfaces is either 100% reflective, 100% transmissive or 50% reflective and 50% transmissive.

Abstract: An method and device suitable for navigation on a wide variety of surfaces is introduced. Specular reflection is used to determine relative motion over typical surfaces. A specific application is a computer mouse.

Abstract: A system for calibrating a spatial light modulator array includes an illumination system and a spatial light modulator array that reflects or transmits light from the illumination system. A projection optical system images the spatial light modulator array onto an image plane. A shearing interferometer creates an interference pattern in the image plane. A controller controls modulation of elements of the spatial light modulator array. The shearing interferometer includes a diffraction grating, a prism, a folding mirror or any other arrangement for generating shear. The shearing interferometer can be a stretching shearing interferometer, a lateral shearing interferometer, or a rotational shearing interferometer. The shearing interferometer may include a diffraction grating with a pitch corresponding to a shear of the light by an integer number of elements. The projection optics resolves each element of the spatial light modulator array in the image plane.

Abstract: An improved, adaptive optics control system having a signal-to-noise ratio-tuned wavefront corrector is disclosed. The system comprises a wavefront corrector, a wavefront sensor, a wavefront reconstructor and a wavefront controller. The wavefront corrector has a surface controlled by a plurality of actuators. The wavefront slope sensor has a subaperture separation mechanism for defining a plurality of subapertures through which the distorted wavefront can pass, each subaperture corresponding to an actuator of the wavefront corrector. The wavefront slope sensor produces a wavefront sensor output signal for each subaperture indicative of the distortion of the wavefront. The wavefront reconstructor is adapted to receive the wavefront sensor output signals and calculate corresponding phase estimates based thereon, each phase estimate having a signal-to-noise ratio.

Abstract: In a method for determining wavefront aberrations for the characterization of imaging characteristics in an optical imaging system, the measurement results from two different measurement methods, which are carried out at successive times, are combined. In this case, at least some of the aberration parameters which are determined in the previous first measurement method are used as a given precondition for determining aberration parameters with the aid of the second measurement method, and are assessed accordingly. This results in a hybrid method, in which the strength of at least two measurement methods are used in a combined form, and specific weaknesses of any one method can be avoided.

Abstract: A system for calibrating a spatial light modulator array includes an illumination system and a spatial light modulator array that reflects or transmits light from the illumination system. A projection optical system images the spatial light modulator array onto an image plane. A shearing interferometer creates an interference pattern in the image plane. A controller controls modulation of elements of the spatial light modulator array. The shearing interferometer includes a diffraction grating, a prism, a folding mirror or any other arrangement for generating shear. The shearing interferometer can be a stretching shearing interferometer, a lateral shearing interferometer, or a rotational shearing interferometer. The shearing interferometer may include a diffraction grating with a pitch corresponding to a shear of the light by an integer number of elements. The projection optics resolves each element of the spatial light modulator array in the image plane.

Abstract: In an interference measuring device, which includes: a coherent beam generating source; a sample to be measured; a lens system for forming an image of the sample to be measured on an observing plane; an interference element for splitting a coherent beam into two systems, and forming an interference image on the observing plane or a plane equivalent thereto; an image pickup element for picking up the interference image on the observing plane; and a calculating device having functions of capturing and storing the interference image converted to electric signals by the image pickup element, and determining the phase distribution changed by the sample to be measured from the interference image by calculation, wherein a means for removing the phase change distribution due to the interference element is provided.

Abstract: A wavelength detector includes an optical structure receiving an input beam, the optical structure outputting at least two wavelength dependent two-beam interference signals. Each wavelength dependent two-beam interference signal has a different phase offset. A detector receives the at least two wavelength dependent two-beam interference signals and outputs an electrical signal representative of each wavelength dependent two-beam interference. A processor receives the at least two electrical signals from the detector and generates a composite control signal. The two-beam interference signals may be created by reflecting light off the two surfaces of the optical structure. The different phase offsets may be created by providing a stepped pattern on one of the surfaces of the optical structure. Phase shifting interferometry techniques may be used to determine the wavelength from the periodic signals.

Abstract: A lateral-shear interferometer utilizes two relatively thick glass plates bonded together in a single block with a tilted air gap between opposing inner surfaces. The thickness of the glass plates is selected to be sufficiently large to separate the output beams from the light reflected from the top and bottom surfaces of the block, thereby eliminating the need for antireflection coatings. The shear interferometer is combined with an external mirror mounted on a tilt stage actuated by a computer-controlled tilt actuator to perform phase-shifting interferometric analysis in conventional manner.

Abstract: Described is an anomaly detector apparatus 10 for detecting an anomaly in a tire comprising: a source of coherent light 18 to shine the light 27 directly onto the tire surface 24 and the light being reflected 32 from the tire; a stressing apparatus 12 which can stress the tire; a reflected light receiving apparatus 40 for receiving the light 32 reflected directly from the tire surface 24 when the tire is in a stressed and unstressed condition; a processor 44 which compares images of reflected light from the reflected light receiving apparatus 40 when the tire is stressed and unstressed thereby ascertaining an anomaly in the tire and generates an output from the comparison; and a display apparatus 46 electronically connected to the processor for displaying the output from the processor.

Abstract: Apparatus for measuring angular changes in the direction of travel of a light beam comprising at least one beam shearing assembly for separating, preferably orthogonally polarized, components of the light beam and introducing a lateral shear between them. An analyzer operates on the components to provide them with a common polarization state. A lens focuses the commonly polarized components of the light beam to a spot in a detector plane, and a detector operates to generate an electrical signal having a phase that varies in accordance with the angular change of the light beam in at least one plane. Electronic means receive the electrical signal, determines the phase therefrom, and converts the phase to the angular change in the direction of travel of the light beam.

Abstract: The invention relates to a method of extending the capture range (CR) of a wavelength monitor for the lasers of a wavelength division multiplex (WDM) transmission system wherein the capture range (CR) comprises one wavelength period (FSR) of a periodic error signal (E) generated with the aid of the wavelength filter (4), the capture range contains a desired wavelength (?0) of a plurality of equidistant wavelengths (?i, ?i+1, ?i+2, . . . ), each of the lasers of the WDM transmission system is set at a desired wavelength (?0) by comparing the error signal (E) with an comparison value (C1 or C2), that is unique in the capture range (CR) for a chosen slope sign, the wavelength period (FSR) of the error signal (E) is set such that it corresponds to double the wavelength spacing (A) of two adjacent wavelengths of the WDM transmission system and the desired wavelength (?0) is set taking into account the slope sign of the error signal (E), and further relates to a wavelength monitor and laser system therefor.

Abstract: A shearing generator comprising: an input light source; an image generator that generates two images of the input light source at an output plane, the image generator comprising a beam splitter that splits light from the input source into at least one pair of interfering light waves at an output thereof, and defines different optical paths for the light propagation of the light waves, said optical paths including at least one phase shifting element that provides for a different phase shift for the two paths.

Abstract: A system for calibrating a spatial light modulator array includes an illumination system and a spatial light modulator array that reflects or transmits light from the illumination system. A projection optical system images the spatial light modulator array onto an image plane. A shearing interferometer creates an interference pattern in the image plane. A controller controls modulation of elements of the spatial light modulator array. The shearing interferometer includes a diffraction grating, a prism, a folding mirror or any other arrangement for generating shear. The shearing interferometer can be a stretching shearing interferometer, a lateral shearing interferometer, or a rotational shearing interferometer. The shearing interferometer may include a diffraction grating with a pitch corresponding to a shear of the light by an integer number of elements. The projection optics resolves each element of the spatial light modulator array in the image plane.

Abstract: Techniques and systems for using optical interferometers to obtain full-field optical measurements of surfaces, such as surfaces of flat panels, patterned surfaces of wafers and substrates. Applications of various shearing interferometers for measuring surfaces are described.

Abstract: The present invention concerns an interferometer in which the input light beam is incident at a non-normal angle of incidence on a pair of reflective interfaces, wherein the front surface is partially reflective and the rear interface inclined at an angle relative to the front face so that the input beam is amplitude split into two spatially offset collimated beam propagating at an angle relative to one another. Lens means are provided for focussing the beams to create a pair of focal spots in the focal plane of said lens means so that the light reflected from a measurement plane in or very near to the focal plane is re-collimated by the same lens used to focus the beams. The light then propagates back through the input beam dividing optic and recombines to cause interference.

Abstract: A lens evaluation method includes diffracting light derived from a lens so that two diffracted rays of different orders (e.g., a 0th-order diffracted ray and a +1st-order diffracted ray) interfere with each other, thereby obtaining a shearing interference figure, and changing phases of the diffracted rays. The method also includes in the shearing interference figure, determining phases of light intensity changes at a plurality of measuring points on a measuring line which passes through a midpoint of a line segment interconnecting optical axes of the two diffracted rays, and determining characteristics (defocus amount, coma, astigmatism, spherical aberration and a higher-order aberration) of the lens based on the phases.