Abstract: A novel method for whole field thin film stress evaluation is provided. Through the provided method, the whole filed thin film stress distribution for an optical thin film would be developed with a commercial interferometer, so that a whole field evaluation for the crack or peel-off of thin film is hence achievable.

Abstract: A method for determining the shape of a rough surface of an object comprises the steps of providing an object having a given roughness related height variation; providing an interferometer for wave front measurement comprising a measurement beam of electromagnetic radiation having a wavelength ? not exceeding 10 times of the roughness related height variation of the object surface, which measurement beam comprises an incoming wave for illuminating the object surface and an outgoing wave comprising radiation from the incoming wave reflected off the object surface; directing the incoming wave of the measurement beam onto the object surface at least two different probing locations, thereby illuminating an areal element of the object surface at each of the probing locations; and measuring the respective phase distribution of the outgoing wave by means of the interferometer of each of the at least two different probing locations.

Abstract: An incoming laser beam is relayed to a steering mirror and a phase correction device. The beam is relayed from the phase correction device to a focal plane array and to a wavefront sensor (WFS). Low order steering mirror tilt corrections can be based on data from the focal plane array. The WFS outputs data on multiple channels to a field programmable gate array (FPGA), with each of the WFS channels corresponding to a subaperture of the beam wavefront. The FPGA calculates phase corrections for each of the subapertures and forwards those corrections to the phase correction device. The FPGA also calculates tilts for the steering mirror based on the WFS output data, which tilts can be used instead of tilts based on focal plane array data. The phase corrections may be based on modulo 2? phase error calculations and/or modal phase error calculations.

Abstract: A method for determining at least one of distortion and de-focus for an optical imaging system. The method includes determining wavefront aberrations in a pupil plane of the optical imaging system by a wavefront measurement method, determining focus offset measured values in an xy-direction and/or z-direction for one or more different illumination settings by a test pattern measurement method with imaging and comparative evaluation of test patterns for the optical imaging system, and determining values for one or more aberration parameters that relate to the distortion and/or image surface from a prescribed relationship between the determined wavefront aberrations and the determined focus offset measured values.

Abstract: A wavelength-variable light source is configured to emit a light with a wavelength (?), which is variable within a scan width (??). An interferometer has a coherent length (?L), which is determinable from (??) and (?). A controller determines an appropriate magnitude of the scan width (??) while a CCD camera captures a fringe image in an exposure time (Te), which is set longer than a time for wavelength scanning.

Abstract: A shape measuring method for measuring a surface shape of a measurement target includes dividing light from a light source into measurement light and reference light, the measurement light being obliquely incident upon a surface of the measurement target, the reference light being incident upon a reference mirror, introducing the measurement light reflected by the measurement target and the reference light reflected by the reference mirror to a photoelectric conversion element, detecting interference light formed by the measurement light and the reference light by the photoelectric conversion element while moving the measurement target, and measuring the surface shape of the measurement target based on an interference signal obtained from the measurement light that has been reflected at the same position on the surface of the measurement target.

Abstract: A method for creating an image of an object includes setting an illumination source at an initial nominal wavelength, illuminating an object with an illumination source to create interference patterns, changing the wavelength of the illumination source to drift from the nominal wavelength to a drift wavelength over a time period that causes a 360° shift in the phase angle of the interference patterns, sampling the interference patterns multiple times during the time period, reconstructing the phase angle of several points on the object, and creating an image of the object based on the sampled and reconstructed information.

Abstract: Preferred embodiments of the present invention are directed to systems for phase measurement which address the problem of phase noise using combinations of a number of strategies including, but not limited to, common-path interferometry, phase referencing, active stabilization and differential measurement. Embodiment are directed to optical devices for imaging small biological objects with light. These embodiments can be applied to the fields of, for example, cellular physiology and neuroscience. These preferred embodiments are based on principles of phase measurements and imaging technologies. The scientific motivation for using phase measurements and imaging technologies is derived from, for example, cellular biology at the sub-micron level which can include, without limitation, imaging origins of dysplasia, cellular communication, neuronal transmission and implementation of the genetic code.

Abstract: A method of combining holograms or phase images of an object is disclosed, where attributes of the data used to record two phase images of overlapping portions of the surface of an object are compared and used to match pixels of the two recordings. A relative tilt angle and direction correction is added, and a third phase image is generated. Phase images of objects which are too large to be imaged in an interferometric imaging system can thus be produced.

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: Embodiments of the present disclosure provide systems and methods for constructing a profile of sample object. Briefly described, in architecture, one embodiment of the system, among others, can be implemented as follows. An interferometer device is used to collect interference images of a sample object at a sequence of angles around the sample object. Accordingly, a controller device rotates the sample object to enable acquisition of the interference images; and a projection generator produces projections of the sample object from the interference images at the sequence of angles. Further, a tomographic device constructs the profile of the optical device from the projections of the interference images. The profile is capable of characterizing small index variations of less than 1×10?4. Other systems and methods are also included.

Abstract: Described is a fringe generator for an interferometric measurement system having improved fringe stability and reproducibility. The fringe generator includes a light source at a characteristic wavelength and a diffractive element to generate a pair of diffracted beams from light received from the light source. The fringe generator also includes a lens to receive the pair of diffracted beams and to image the plane of the diffractive element onto an object to be measured. The generated fringe pattern is substantially independent to a change in the position of the light source relative to the lens and a change in the characteristic wavelength of the light source. A broadband light source can be used and the resulting broadband fringe pattern is substantially independent to a change in the position of the light source relative to the lens and to a change in the spectral distribution of the broadband light source.

Abstract: A method of wavelength selection control is disclosed.

Abstract: A method for obtaining an image of a tooth obtains an area image of the tooth (20) surface and identifies a region of interest from the area image by positioning a marker (146) on the area image. The marker (146) corresponds to at least a portion of the region of interest and identifies a scanning area. An optical coherence tomography (OCT) image is then obtained over the scanning area.

Abstract: There are carried out a first measurement operation for measuring the shape of a front surface of a sample held in a held state, a second measurement operation for measuring the shape of a back surface of the sample held in the same state, and a third measurement operation for measuring the shape of the back surface of the sample held so as to cause inverse distortion. First data are acquired on the basis of the front surface shape data obtained through the first measurement operation and the back surface shape data obtained through the second measurement operation. Second data are obtained on the basis of the front surface shape data obtained through the first measurement operation and the back surface shape data obtained through the third measurement operation. Holding distortion is determined on the basis of the first and second data.

Abstract: An optical nulling apparatus for testing an optical surface includes an aspheric mirror having a reflecting surface for imaging light near or onto the optical surface under test, where the aspheric mirror is configured to reduce spherical aberration of the optical surface under test. The apparatus includes a light source for emitting light toward the aspheric mirror, the light source longitudinally aligned with the aspheric mirror and the optical surface under test. The aspheric mirror is disposed between the light source and the optical surface under test, and the emitted light is reflected off the reflecting surface of the aspheric mirror and imaged near or onto the optical surface under test. An optical measuring device is disposed between the light source and the aspheric mirror, where light reflected from the optical surface under test enters the optical measuring device.

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

Abstract: A method and apparatus for wavefront analysis including obtaining a plurality of differently phase changed transformed wavefronts corresponding to a wavefront being analyzed which has an amplitude and a phase, obtaining a plurality of intensity maps of the plurality of phase changed transformed wavefronts and employing the plurality of intensity maps to obtain an output indicating the amplitude and phase of the wavefront being analyzed.

Abstract: A method of processing a substrate on which a layer of photoresist has been applied, the method involving: exposing the layer of photoresist to radiation that carries spatial information to generate exposure-induced changes in the layer of photoresist that form a pattern having one or more features; and before developing the exposed photoresist, interferometrically obtaining measurements of the pattern in the exposed layer of photoresist for determining at least one of (1) locations of the one or more features of the pattern and (2) magnitudes of the exposure-induced changes.

Abstract: In some embodiments, an optical imaging system comprises a non-destructive optical device that obtains information concerning a target object and a X,Y positioning system that is capable of positioning one or both of the target object and the optical device to pre-determined offset locations more closely spaced than the obtainable resolution of the optical device. A first “base” image is produced and then overlapping additional images may be produced by the positioning one or both of the target object and the optical device to the pre-determined locations. The first image and the additional images may be combined to produce a single combined image that contains inherently more information than the first image or any of the additional images alone. The combined image then may be digitally restored and enhanced to produce an image with a greater resolution than the optical device yields.

Abstract: An interferometry method using a laser of nominally fixed—but unknown and changing—frequency and phase angle, for example, attributable to laser drift. The interference pattern is periodically sampled at a frequency considerably higher than the phase shift of the object. The wavelength is reconstructed from the sampled patterns using a correlation algorithm. The phase angle is determined using an n-bucket algorithm. After all of the complex information has been determined at all of the multiple wavelengths, the surface of the object is calculated using conventional interferometry techniques. Accordingly, laser drift—typically considered a negative attribute—is used positively.

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: A profilometry apparatus is provided. The profilometry apparatus includes a fringe projection device configured to project a fringe pattern on an object and an optical unit configured to capture an image of a distorted fringe pattern modulated by the object. The profilometry apparatus also includes a signal processing unit configured to process the captured image from the optical unit to filter noise from the image and to obtain real-time estimation of parameters associated with manufacture or repair of the object.

Abstract: A device, a microlithography projection exposure system, and a method for the determination of imaging errors of an optical imaging system using a radiation-superposition measuring technique which operates with lateral phase offset, having an optical element arranged on the object side of the imaging system, having a first periodic structure on the object side with a predetermined periodicity direction, an optical element arranged on the image side of the imaging system, having a second periodic structure on the image side with a periodicity direction corresponding to the first periodic structure, and a detector to detect the superposition pattern of an image of the first periodic structure with the second periodic structure.

Abstract: Methods and apparatus based on optical homodyne displacement interferometry, optical coherent-domain reflectometry (OCDR), and optical interferometric imaging are disclosed for overlay, alignment mark, and critical dimension (CD) metrologies that are applicable to microlithography applications and integrated circuit (IC) and mask fabrication and to the detection and location of defects in/on unpatterned and patterned wafers and masks. The metrologies may also be used in advanced process control (APC), in determination of wafer induced shifts (WIS), and in the determination of optical proximity corrections (OPC).

Abstract: Apparatus for splitting, imaging, and measuring wavefronts with a reference wavefront and an object wavefront. A wavefront-combining element receives and combines into a combined wavefront an object wavefront from an object and a reference wavefront. A wavefront-splitting element splits the combined wavefront into a plurality of sub-wavefronts in such a way that each of the sub-wavefronts is substantially contiguous with at least one other sub-wavefront. The wavefront-splitting element may shift the relative phase between the reference wavefront and the object wavefront of the sub-wavefronts to yield a respective plurality of phase-shifted sub-wavefronts. The wavefront-splitting element may then interfering the reference and object wavefronts of the phase-shifted sub-wavefronts to yield a respective plurality of phase-shifted interferograms. An imaging element receives and images the phase-shifted interferograms.

Abstract: A method for optical evaluation of a sample includes scanning a beam of coherent radiation over the sample, whereby the radiation is scattered from the sample, while directing a portion of the scanning beam toward a diffraction grating so that the portion of the beam is scanned over the grating, whereby a frequency-shifted reference beam is diffracted from the grating. The scattered radiation and the frequency-shifted reference beam are combined at a detector to generate an optical heterodyne signal.

Abstract: An interferometric profiler is used to measure object motion by modifying the motion of the scanner so that the phase variation at each scanning step is kept within the acceptable limits of the algorithm used to calculate phase changes. The scanner motion is so manipulated on the basis of prior knowledge about the nature of the object motion, or knowledge obtained by pre-calibration, or by real-time feedback based on current measurements. The object motion is recovered from the scanning information by subtracting the scanner position from the object position as it evolves during the scan.

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

Abstract: The invention is a method of determining the phase difference between two interferometric images. The method includes the steps of measuring the intensities of the two beam arms, and measuring the intensities of the interfering beam arms at two different times (two frames). From the recorded data, the phase angle between the arms can be determined for each frame. These frame phase angles subtracted, and the sine of the difference is taken. The resulting data set is examined to determine a multiplicative factor that converts the minimum and maximum to the bounds of the sine function (?1, +1). This multiplicative factor is applied to a bounded trig function of the difference of the frame angles, and the inverse of the bounded trig function is taken, resulting in the phase difference between frames.

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

Abstract: A phase shifting interferometric method and apparatus comprises generating at least four different phase shifts and recording interferograms corresponding to the different phase settings and recording interferograms corresponding to the different phase settings. In the analysis of the recorded interferograms the generated phase shifts between the at least four different phase settings are determined from the measurement, i.e. from the recorded interferograms. A model simulating the interferogram intensities may be used for determining the phase shifts. The phase shifts are free adaptable parameters of the model.

Abstract: Exemplary apparatus and method for obtaining information associated with at least one image of at least one portion of a sample can be provided. For example, at least one first electro-magnetic radiation can be provided from the at least one portion (e.g., using a first electro-magnetic radiation guiding arrangement which is configured to provide). A plurality of spatial frequency bands of the image associated with the first electro-magnetic radiation can be generated. Further, at least one second electro-magnetic radiation which is associated with the spatial frequency bands of the image can be received (e.g., using a second arrangement), and the image can be reconstructed based on the spatial frequency bands.

Abstract: A sample inclination measuring method rotates, by a predetermined angle with respect to an interferometer apparatus, a columnar member having a leading end face in a planar form while the columnar member is held by a clamping apparatus, detects a relative angle between a reference surface of the interferometer apparatus and the leading end face at each of two rotational positions, and measures the inclination of the axis of the columnar member by using a predetermined arithmetic expression according to thus detected two angles.

Abstract: A method of determining at least one optical property of a projection exposure system is described, wherein the exposure system includes a beam delivery system having a light source for generating an exposure optical beam having light of a first wavelength (?1) and a second wavelength (?2), wherein a first ratio is defined as an intensity of light ?2 to an intensity of light ?1 in the exposure optical beam. The method includes supplying at least one measuring optical beam including light of at least ?1 to the projection optical system, detecting wavefronts having traversed the projection optical system, and determining an optical property in dependence of the detected wavefronts, wherein a second ratio of an intensity of light of ?2 to an intensity of light of ?1 in the measuring optical beam being incident on the detector of the wavefront detection system is less than the first ratio.

Abstract: Methods, systems, and articles of manufacture consistent with the present invention identify a flaw in a structure by comparing a first interference pattern resulting from a first wave signal and a second wave signal propagating through the structure to a second interference pattern resulting from the first wave signal and the second wave signal propagating through the structure. The second interference pattern is obtained after obtaining the first interference pattern. It is determined whether there is a flaw in the structure by determining whether the first interference pattern deviates from the second interference pattern by a predetermined variance.

Abstract: Method of optical measuring the microrelief of an object using a modulation interference microscope. An input coherent monochromatic polarized light flux is split into an object light beam exposing the object and a reference beam. The light flux intensity is redistributed between the object and reference beams. Thereafter, polarization modulation is performed separately for the object beam and the reference beam. The polarized object beam is reflected onto the object plane to expose the object field. Amplitude modulation is performed by changing the intensity ratio between the object beam and the reference beam. A fraction of the light at a pixel caused by the object beam with respect to the total light falling on the pixel is determined.

Abstract: An apparatus including: (i) an interferometer positioned to derive measurement and reference wavefronts from a source of electromagnetic radiation, wherein the interferometer is configured to direct the measurement wavefront to reflect from a measurement surface and the reference wavefront to reflect from a reference surface, and further directs reflected measurement and reflected reference wavefronts to overlap with one another and to form an interference pattern; (ii) an auxiliary optic having a curved reflective surface positioned to redirect the measurement wavefront between the interferometer and the measurement surface; and (iii) a translation stage, wherein paths for the measurement and reference wavefronts define an optical measurement surface corresponding to a theoretical test surface that would reflect the measurement wavefront to produce a zero optical path length difference between the measurement and reference wavefronts, and wherein the translation stage is configured to scan the optical measur

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: A surface inspecting apparatus for inspecting a shape of a surface of an object to be inspected is disclosed. The surface inspecting apparatus includes a mounting base for mounting the object, a positioning device for positioning the object to an inspecting position on the mounting base, a memory for storing position specifying information for specifying a two-dimensional position of the object when the object is positioned, an inputting device for inputting an outer shape data of the object, and edge position determining device for acquiring an edge position of the object based on the stored position specifying information and the inputted outer shape data.

Abstract: A method of processing an optical substrate having a convex surface comprises an interferometric measurement using a beam of diverging measuring light traversing the substrate and reflected from a concave mirror.

Abstract: An improved wavefront sensor for characterizing phase distortions in incident light including optical elements that spatially sample the incident light and form a dispersed spot with a fringe pattern corresponding to samples of the incident light. An imaging device captures an image of the dispersed spot with said fringe pattern formed by said optical elements. And an image processor that analyzes the spectral components of the fringe pattern of a given dispersed spot to derive a measure of the local phase distortion without ambiguity in the corresponding sample of incident light. The optical elements may comprise refractive elements, diffractive elements or a combination thereof (such as a grism). The wavefront sensor may be part of an adaptive optic system (such as a large-aperture space telescope) to enable the measurement and correction of large phase steps across adjacent mirror segments of a deformable mirror.

Abstract: An interferometry system including: a first imaging system that directs a measurement beam at an object to produce a return measurement beam from the object, that directs the return measurement beam onto an image plane, and that delivers a reference beam to the image plane; and a beam combining element in the image plane, said beam combining element comprising a first layer containing an array of sagittal slits and a second layer containing an array of tangential slits, wherein each slit of the array of sagittal slits is aligned with a corresponding different slit of the array of tangential slits, wherein the beam combining element combines the return measurement beam with the reference beam to produce an array of interference beams.

Abstract: The present invention makes it possible to reliably hold a computer-generated hologram 17 and a sample surface 18a in ideal design positions and to perform interference measurements on the surface shape of the sample surface 18a by holding the computer-generated hologram 17 in a predetermined attitude by using a retaining member, and interposing a spacer 45 between this retaining member and the object so that relative positioning of both the computer-generated hologram 17 and the sample surface 18a is performed. Light transmission type targets used for alignment are respectively disposed on the four corners of the frame body of the CGH 17 and the four corners of the measurement mirror 18, and the system is devised so that images of these targets can be obtained by an image focusing lens 43 and CCD camera 44, thus making it possible to check the adjustment of the alignment of the CGH 17 and sample surface 18a.

Abstract: A method including: imaging test light emerging from a test object over a range of angles to interfere with reference light on a detector, wherein the test and reference light are derived from a common source; for each of the angles, simultaneously varying an optical path length difference from the source to the detector between interfering portions of the test and reference light at a rate that depends on the angle at which the test light emerges from the test object; and determining an angle-dependence of an optical property of the test object based on the interference between the test and reference light as the optical path length difference is varied for each of the angles.

Abstract: A method is described that involves measuring a first set of interferometer fringe line disturbances against pre-determined measurement scale information in order to generate a first set of profiles that describe the topography of a sample that is placed upon a sample stage associated with the interferometer. The first set of profiles map to traces that run over a first axis of the sample and the sample stage. The traces have a recognized spacing between one another along a second axis of the sample and the sample stage. The method also involves adjusting the relative position of the traces to the sample so as to create a second set of fringe line disturbances. The method also involves measuring, the second set of interferometer fringe line disturbances against the pre-determined measurement scale information in order to generate a second set of profiles that describe the topography of the sample.

Abstract: Methods and systems for measuring optical aberrations of an eye are provided. In one embodiment, the present invention provides transmitting light from the eye along an optical path to an aberration sensor. An adaptive optic is disposed along the optical path between a target optical system and the aberration sensor. Aberrations of the adaptive optic can be adjusted in response to a signal generated by the aberration sensor so as to provide a desired sensed aberration. The shape of the adjusted adaptive optic can be determined with the aberration sensor by transmitting an adaptive optic configuration measurement beam along the optical path.

Abstract: Disclosed are a system and a method for determining coordinates of a three-dimensional measurer probe using a beam phase interference method. Two optical fibers are mounted inside the probe, and detecting means obtains an interference pattern generated by beam emitted from a point beam source mounted at ends of the optical fibers. After that, wave front of the interference pattern is measured and a location of the point beam source is determined through a nonlinear optimization from the wave front, and thereby the coordinates of the three-dimensional measurer probe are set. Because the two optical fibers of the inside of the probe to be measured are located in close vicinity to the three-dimensional object, the present measuring system and method can reduce a measurement error, make a structure of the system simple, and thereby reduce a manufacturing cost.

Abstract: Frequency-scanning interferometry is applied to common-path interferometers for measuring topographical features of test objects. A reference element located adjacent to a test object functions as both a beamsplitter and a reference surface. A first portion of a measuring beam reflects from the reference surface of the reference element as a reference beam, and a second portion of the measuring beam transmits through the reference element to and from a surface of the test object as an object beam. Both beams are conveyed along a common path to a detector that records a plurality of intensity variations produced by constructive and destructive interference between localized portions of the object and reference beams associated with different transverse coordinates on the test object surface.

Abstract: A simple digital holographic apparatus and method allow reconstruction of three-dimensional objects with a very narrow depth of focus or high axial resolution. A number of holograms are optically generated using different wavelengths spaced at regular intervals. They are recorded, such as on a digital camera, and are reconstructed numerically. Multiwavelength interference of the holograms results in contour planes of very small thickness and wide separation. Objects at different distances from the hologram plane are imaged clearly and independently with complete suppression of the out-of-focus images. The technique is uniquely available only in digital holography and has applications in holographic microscopy.