JP2005537518A - High-speed direct digital holography acquisition of objects off-axis illuminated by multiple illumination sources - Google Patents

Abstract

A system and method for fast acquisition of fused off-axis illuminated direct digital holography is described. A method for recording a plurality of off-axis object illuminated spatial heterodyne holograms, wherein the off-axis object illuminated spatial heterodyne hologram includes a spatial heterodyne fringe for Fourier analysis, the method comprising: Using a first illumination source (120) to digitally record a first off-axis object illuminated spatial heterodyne hologram including a spatial heterodyne fringe for Fourier analysis, and a second illumination source of the interferometer (120) and digitally recording a second off-axis object illuminated spatial heterodyne hologram including a spatial heterodyne fringe for Fourier analysis.

Description

(Background of the Invention)
(Field of Invention)
The present application relates generally to the field of direct digital holography (interferometry). More specifically, the present invention relates to high-speed acquisition of off-axis illumination holograms for direct digital holography.

(Description of related applications)
Prior art direct digital holography (DDH), sometimes referred to as direct digital interferometry, is well known to those skilled in the art. For example, FIG. 1 shows one schematic embodiment of a DDH system. Light from laser source 105 is magnified by beam expander / spatial filter 110 and travels through lens 115. Thereafter, the expanded and filtered light travels toward the beam splitter 120. The beam splitter 120 may partially reflect. The portion of the light reflected from the beam splitter 120 constitutes an object beam 125 that travels toward the object 130. A portion of the object beam 125 is reflected by the object 130 and travels through the beam splitter 120 toward the focusing lens 145. The light then travels through a focusing lens 145 toward a charge coupled device (CCD) camera (not shown).

  The portion of light from lens 115 that passes through beam splitter 120 constitutes reference beam 135. The reference beam 135 is reflected from the mirror 140 at a small angle. Thereafter, the reference beam 135 reflected from the mirror travels toward the beam splitter 120. Thereafter, the portion of the reference beam 135 reflected from the beam splitter 120 travels through the focusing lens 145 and travels toward the CCD camera (not shown). The object beam 125 from the focusing lens 145 and the reference beam 135 from the focusing lens 145 constitute a plurality of objectives and reference waves 150 and interfere at the CCD to produce a hologram interference pattern as described in US Pat. No. 6,078,392. Give rise to properties.

  In FIG. 1, the object beam 125 is parallel and coincident with the optical axis 127. This type of DDH setting can be referred to as on-axis illumination.

  The limitation of this technology was that the imaging resolution of the DDH system was limited by the optical components of the system. The most notable limitation of optical components is the aperture stop, which is necessary to prevent image quality deterioration due to aberrations. For the two-dimensional Fourier plane, only the spatial frequency of the object in the circle with the radius q0 can be transmitted. For axial illumination, the aperture with radius q0 appears to be centered on zero spatial frequency (q = 0). Therefore, an effort is needed to enable transmission of spatial frequencies outside the circle of radius q0.

(Summary of Invention)
The following aspects of the present invention are needed. Of course, the present invention is not limited to these aspects.

  According to one aspect of the present invention, a process for recording a plurality of off-axis illuminated spatial heterodyne holograms, each off-axis illuminated spatial heterodyne hologram includes a spatial heterodyne fringe for Fourier analysis, the process comprising: Digitally recording a first off-axis object illuminated spatial heterodyne hologram including a spatial heterodyne fringe for Fourier analysis using a first illumination source of the interferometer; and a second illumination of the interferometer Digitally recording a second off-axis object illuminated spatial heterodyne hologram including a spatial heterodyne fringe for Fourier analysis using the source.

  According to another aspect of the present invention, a machine operable to digitally record a plurality of off-axis illuminated spatial heterodyne holograms including spatial heterodyne fringes for Fourier analysis, the machine comprising a plurality of An illumination source, a beam splitter optically coupled to the plurality of illumination sources, a reference beam mirror optically coupled to the beam splitter, a focusing lens optically coupled to the reference beam mirror, and a focusing lens An optically coupled digital recorder and a computer that performs Fourier transform, applies digital filters, and performs inverse Fourier transform, the reference beam is incident on the reference beam mirror at a non-standard angle, and the object beam is focused The object is incident on the object at an angle with respect to the optical axis defined by the lens, and the reference beam and object beam are An off-axis illuminated spatial heterodyne hologram containing a spatial heterodyne fringe for Fourier analysis that is focused on the focal plane of the tall recorder and recorded by a digital recorder, and the computer records a recorded off-axis containing the spatial heterodyne fringe The axis of the illuminated space heterodyne hologram is transformed into Fourier space so that it is located at the top of the heterodyne carrier frequency defined by the angle between the reference beam and the object beam, and before the inverse Fourier transform is performed, Cut off surrounding signals.

  These and other aspects of the invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. The following description, however, is not intended to be limiting, although various embodiments of the invention and many specific details are set forth. Many alternatives, modifications, additions, and / or reconfigurations may be made within the scope of the present invention without departing from the spirit thereof. The present invention includes all such alternatives, modifications, additions and / or reconfigurations.

  The accompanying drawings, which form a part of this specification, are included to illustrate certain aspects of the present invention. The clearer concepts of the present invention, and the components and operations of the systems provided by the present invention, will be more readily apparent by reference to non-limiting embodiments, which are examples shown in the drawings. Will. The invention will be better understood by reference to one or more of these drawings in combination with the description presented in the specification. Note that the features shown in the drawings do not necessarily follow a uniform scale.

(Description of Preferred Embodiment)
The invention and its various features and advantages are more fully described by reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Well-known initial materials, processing techniques, components, and apparatus have been omitted so as not to obscure the present invention in unnecessary detail. However, it should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are exemplary and not restrictive. Various alternatives, modifications, additions and / or rearrangements within the spirit and / or scope of the underlying inventive concept will become apparent to those skilled in the art from this disclosure.

  Within this application, several publications are referenced by Arabic numerals in parentheses. Full citations for these and other publications may be found after the paragraph titled Reference at the end of the specification and immediately preceding the claims. The entire disclosures of all these publications are hereby expressly cited for the purpose of providing a background to the invention and illustrating the state of the art.

  In general, the relevant background of the present invention may include acquiring, storing, and / or reproducing digital data. The relevant background of the present invention may include processing digital data representing an image. Also, relevant background of the present invention may include converting data from multiple images to a composite image.

  The present invention may include a method for obtaining an improved resolution holographic image from a direct digital holography system using off-axis illumination. The present invention may also include an apparatus for acquiring improved resolution holographic images in a direct digital holography (DDH) system using off-axis illumination.

  In general, an object to be observed (imaged) is optically coupled to an illumination source via one or more optical components. As described with respect to FIG. 1, the illumination beam typically passes through the center of the objective lens of interest (ie, the lens system) along the optical axis and thus parallel to the optical axis. This type of DDH configuration can be referred to as “on-axis illumination”, and this configuration obtains the spatial frequency (q) of the object to a certain limit (q0) determined by the aperture of the objective lens. Can do.

  The present invention may include an “on-axis illumination” scenario. In this case, the illumination source is disposed in the horizontal direction so that the beam passes through the objective lens parallel to the optical axis but off the center. Due to the focusing effect of the objective lens, the illumination is incident on the object at an angle with respect to the optical axis. With this eccentric illumination, a higher spatial frequency (q> q0) of the object than in the on-axis illumination can pass through the aperture of the objective lens and can therefore be observed. This is an important advantage of the present invention.

  The present invention may include an extended DDH system (apparatus) adapted to digitally capture on-axis and one or more off-axis illuminated holograms of the same object. The present invention may also include analyzing and / or processing (fusion) digitally captured data. The resulting fusion image encompasses a wider range of spatial frequencies than in any original hologram, thus significantly increasing the nominal imaging resolution of the system compared to when off-axis illumination data is unavailable. .

  As noted above, the imaging resolution of the basic DDH system is limited by the optical components, particularly the aperture stop required to prevent image quality degradation due to aberrations. This means that the optical component of the DDH system can only transmit the spatial frequency of the object in the circle with the radius q0. In the case of on-axis illumination, an opening of radius q0 appears centered at 0 spatial frequency (q = 0). In the case of off-axis illumination, the opening with the radius q0 appears shifted (for example, on the left) in the frequency domain. This suggests that a spatial frequency of q> q0 is transmitted in the direction in which the aperture is shifted. The disadvantage is that spatial frequencies where q is close to q0 are “lost” in the opposite direction. By acquiring a second image in which the illumination is offset in the opposite direction, the aperture appears off (eg, to the right), so the “lost” spatial frequency from the first image has an additional frequency of q0 or higher. To be recovered. As a result of fusing information from two images, one image with better resolution is obtained. Since DDH records phase information on the composite image wave, the information from both (or more) images is fused to yield surprisingly advantageous results. The present invention improves the resolution of general object structures regardless of orientation.

  The present invention may include an extension of the basic DDH system to automatically capture both on-axis and off-axis illuminated holograms. The present invention may also include a method for analyzing and fusing the results of these holograms so that the observed object is displayed at a higher spatial resolution than is available in conventional DDH technology.

  As can be seen in FIG. 1, the object beam 125 is parallel to the optical axis 127. As described above, this setting can be referred to as on-axis illumination. On the other hand, off-axis illumination refers to the case where the object beam 125 is incident on the object 130 at an angle with respect to the optical axis 127 (an example is illustrated by the object teams 215 and 305 shown in FIG. 3). ) There are many ways to achieve off-axis illumination. The approaches presented below are only representative and are therefore intended to be non-limiting examples.

  With reference to FIGS. 2 and 3, one embodiment of an off-axis illumination DDH apparatus is illustrated. 2 and 3, there are two major corrections from FIG. The first correction is that the laser source 105, beam expander / spatial filter 110, and lens 115 are grouped into a movable housing 205 controlled by a computer. The housing 205 is movable along an axis that is practically parallel to the optical axis 127. More specifically, the housing 205 is movable along an axis that is substantially coplanar with the normal of the beam splitter 120.

  With further reference to FIGS. 2 and 3, the second correction point is that an object objective lens 210 is added. In FIG. 2, the laser source housing 205 is arranged so that the object beam 125 is reflected from the beam splitter 120 and passes through the center of the object objective lens 210. Thereafter, the object beam 125 leaves the object objective lens 210 and enters the object 130 around the optical axis 127. In this configuration, on-axis illumination is realized and the system of FIG. 2 is effectively the same as FIG.

  However, in FIG. 3, the laser source housing 205 is offset (up in this particular configuration) so that the object beam 125 passes through the object objective lens 210 off its center. Of course, alternatively, the laser source housing 205 can be offset downward. Due to the focusing characteristic of the object objective lens 210, the object beam 215 leaving the object objective lens 210 is incident on the object 130 at an angle with respect to the optical axis 127, so that off-axis illumination is realized. Thus, the object beam 215 can be incident on an object that is not substantially parallel to the optical axis 127. The object beam 305 reflected from the object passes through the object objective lens 210 from the center and passes again, but due to the optical characteristics of the object objective lens 210 and the focusing lens 150, the CCD (not shown) I) Focus on the top. In the case of off-axis illumination, the diffraction property (1) suggests that the hologram formed in the CCD due to interference between the object beam 305 and the reference beam 135 contains some spatial frequency of the object that is not observed with on-axis illumination. To do.

  Thus, the present invention can include an apparatus operable to digitally record spatial heterodyne holograms including spatial heterodyne fringes for Fourier analysis. The apparatus includes a laser, a beam splitter optically coupled to the laser, a reference beam mirror optically coupled to the beam splitter, an object optically coupled to the beam splitter, a reference beam mirror, and A focusing lens optically coupled to both of the objects, a digital recorder optically coupled to the focusing lens, a computer that performs Fourier transform, applies a digital filter, and performs inverse Fourier transform, see The beam is incident on the reference beam mirror at a non-standard angle, the object beam is incident on the object at an angle with respect to the optical axis defined by the focusing lens, and the reference beam and object beam include a plurality of simultaneous reference and object waves. And is recorded by the digital recorder after being focused on the focal plane of the digital recorder by the focusing lens Forming a spatial heterodyne hologram containing a spatial heterodyne fringe for analysis, and the computer converts the axis of the recorded spatial heterodyne hologram containing the spatial heterodyne fringe to Fourier space, depending on the angle between the reference beam and the object beam It is positioned at the upper end of the specified heterodyne carrier frequency, and the signal around the original origin is cut off before performing the inverse Fourier transform. The apparatus may include an object objective lens optically coupled between the beam splitter and the object. The apparatus can include an aperture stop coupled between the object and the focusing lens. The beam splitter, reference beam mirror, and digital recorder can define a Michelson shape. The beam splitter, reference beam mirror, and digital recorder can define a Mach-Zehnder shape. The apparatus may include a digital storage medium coupled to a computer that performs a Fourier transform, applies a digital filter, and performs an inverse Fourier transform. The digital recorder may include a CCD camera 350 that defines pixels. The apparatus can include a magnifier / spatial filter 230 optically coupled between the laser and the beam splitter. The angle between the reference beam and the object beam and the magnification given by the focusing lens can be chosen so that the digital recorder resolves the features of the spatial heterodyne hologram including the spatial heterodyne fringe for Fourier analysis. Two fringes with two pixels per fringe can be provided to resolve certain features of the digital recorder. The present invention may include a spatial heterodyne hologram created by the above-described apparatus and implemented on a computer readable medium.

  Thus, the present invention can include a method of recording a spatial heterodyne hologram including a spatial heterodyne fringe for Fourier analysis. The method separates the laser beam into a reference beam and an object beam, reflects the reference beam from the reference mirror at a non-standard angle, and targets the object beam at an angle relative to the optical axis defined by the focusing lens. A spatial heterodyne hologram including a spatial heterodyne fringe for Fourier analysis is created by focusing the reference beam and the object beam, which constitute a plurality of simultaneous reference and object waves, in the focal plane of the digital recorder. Fourier analysis by forming and transforming the axis of the recorded spatial heterodyne hologram to Fourier space so that it is located at the top of the heterodyne carrier frequency defined by the angle between the reference beam and the object beam Spatial heterodyes including spatial heterodyne fringes for Includes analyzing the hologram, and applying a digital filter to cut off the signals around the original origin, then, and performing an inverse Fourier transform. The method includes reflecting the object beam from the object at an angle relative to the optical axis defined by the focusing lens and reflecting the object beam from the object at an angle relative to the optical axis defined by the focusing lens. And diffracting the object beam by an object objective lens. Transforming the axis of the recorded spatial heterodyne hologram to Fourier space can include transforming with an extended Fourier transform. The step of digitally recording can include detecting the beam with a CCD camera that defines the pixels. The off-axis illuminated space heterodyne hologram may be an off-axis illuminated space low frequency heterodyne hologram. The phrase low frequency suggests that the fundamental fringe spatial frequency is below the Nyquist sampling limit. The method may also include storing a spatial heterodyne hologram that includes a spatial heterodyne fringe for Fourier analysis. The method may also include reconstructing a Fourier analyzed spatial heterodyne hologram. The method may also include transmitting a Fourier analyzed spatial heterodyne hologram. The method may also include a spatial heterodyne hologram produced by the above method and implemented on a computer readable medium.

(High speed acquisition)
In FIG. 3, the illumination source housing 120 is mechanically moved so that the object beam 130 passes through the object objective lens 135 away from the center thereof. If only a single object illumination source is used, this suggests that the object illumination source needs to be mechanically moved to capture holograms that are continuously differently illuminated. Such mechanical movement can be very slow. The mechanical movement of the illumination source can limit the application of off-axis techniques in time-constrained scenarios. Therefore, efforts are needed to address the need for high speed off-axis lighting performance.

  The present invention acquires improved resolution holographic images at a much faster rate than the prior art by combining the results of multiple differently illuminated holograms in a direct digital holography (DDH) system. Apparatus and method can be included. The present invention uses a plurality of illumination sources. The present invention may include a plurality of illumination sources that are physically arranged to achieve a plurality of illumination conditions. The present invention may include a plurality of computer controlled sources that are quickly and sequentially switched off and on. By reducing the physical placement of lighting and the associated time costs, the present invention allows for off-axis lighting and the associated imaging resolution improvements, even in time-constrained environments that were not previously applicable. Make applicable.

  With reference to FIG. 4, the present invention may include multiple illumination sources 120. Note that FIG. 4 uses five sources only as representative examples. As will be apparent, the number of illumination sources can vary depending on the specific needs. Multiple illumination sources may be computer controlled so that they can be switched off and on quickly and in succession, thereby allowing multiple holograms that are illuminated differently without physically moving any components. Can be captured. The result is much more time savings. This is because the method for quickly switching the illumination source (well known to those skilled in the art) takes much less time than physical movement. However, the system may remain physically moving to provide more flexibility. By saving time by quickly activating the illumination source, the present invention has been able to apply multiple off-axis illumination (and subsequent resolution improvements) only once with single illumination imaging. It can also be applied to scenarios with time constraints.

  The embodiment shown in FIG. 4 shows a planar array of alternately arranged lasers as a structure for performing a function of quickly switching a plurality of off-axis illumination angles, but a function of quickly switching a plurality of off-axis illumination angles. The structure for performing can be other structures capable of quickly switching between multiple off-axis illumination angles, such as parallel (planar) arrays, radial (planar) ) Arrays, or polygonal (planar) arrays.

  The structure of the disclosed embodiment as a structure that functions to align the source, beam expander / spatial filter, and lens so that the object beam passes through or off the center of the object objective lens. One of them shows a computer-controlled movable housing, but the structure that performs the function of aligning the source, beam expander / spatial filter, and lens allows the object beam to pass through the center of the object objective lens. Or other structures that can perform the function of aligning the object beam so that it passes through or off its center, such as a beam splitter, mirror, object objective lens, etc. Movable platforms that position objects, focusing lenses, and CCD cameras relative to the source, beam expander / spatial filter, and lens, or others A series of movable optical component (e.g., a mirror) as an example, or as another example includes a flexible optical fiber and / or cable.

  The terms “a and an” as used herein are defined as one or more. As used herein, the term “plurality” is defined as two or more. As used herein, the term “another” is defined as a second or more. As used herein, the terms “including” and / or “having” are defined as “comprising” (ie, an open language). As used herein, the term “coupled” has been referred to as “connected”, but it is not necessarily direct or mechanical. As used herein, the term “approximately” is defined as at least close to a predetermined value (eg, preferably within 10%, more preferably within 1%, most preferably within 0.1%). The As used herein, the term “substantially” is defined as “largely”, but is not necessarily the entire specified. As used herein, the term “generally” is defined as at least close to a predetermined state. As used herein, the term “deploying” refers to “designing”, “building”, “shipping”, “installing”, and And / or defined as “operating”. As used herein, the term “means” is defined as hardware, firmware, and / or software for achieving a result. The term “program” or “computer program” as used herein is defined as a sequence of instructions designed to execute on a computer system. A program or computer program executes on a subroutine, function, procedure, object method, object implementation, potential application, applet, servlet, source code, object code, shared / dynamic load library, and / or computer system May include other sequences of instructions designed for. As used herein, the term “low-frequency” may be defined as implying that the basic fringe spatial frequency is below the Nyquist sampling limit.

(Actual application of the present invention)
A practical application of the present invention that is valuable in science and technology is metrology. The present invention is useful in connection with microelectronic (mechanical) manufacturing, such as for semiconductor testing. The present invention is also useful in connection with nanotechnology research, development, and manufacturing, such as nanovisualization or nanomeasurement. The present invention is useful in connection with interferometers that use digital processing and / or digital data acquisition, such as, for example, direct digital holography tools based on electronic holography. There are virtually countless uses of the present invention, all of which need not be detailed here.

(Advantages of the present invention)
A method, apparatus, and / or computer program that represents an embodiment of the present invention may be cost-effective and advantageous for at least the following reasons. The present invention provides a plurality of illumination sources. The present invention provides for fast acquisition of multiple holograms that are illuminated differently. The present invention can provide computer control of object illumination. The present invention can provide for fusing results from multiple holograms. The present invention can provide much higher imaging resolution. The present invention improves quality and lowers costs compared to previous efforts.

  All disclosed embodiments of the invention disclosed herein can be made and used without undue experimentation in light of the disclosure. The present invention is not limited by the theoretical description provided herein. Although the best mode for carrying out the present invention examined by the inventors has been disclosed, the practice of the present invention is not limited thereto. Thus, it will be appreciated by one skilled in the art that the present invention may be practiced otherwise than as specifically described herein.

  Further, each component need not be combined with the disclosed configuration, but could be combined with virtually any configuration. Further, changes may be made in the sequence of steps including the steps or methods described herein. Further, although the devices described herein may be separate modules, it will be apparent that the devices may be integrated into the associated system. Moreover, all disclosed components and features of each disclosed embodiment may be combined with or taken from the disclosed components and features of each of the other disclosed embodiments, except where incompatible with each other. Can be replaced.

  It will be apparent that various substitutions, modifications, additions and / or reconfigurations of features of the invention may be made without departing from the spirit and / or scope of the underlying inventive concept. The spirit and / or scope of the underlying inventive concept as defined by the appended claims and their equivalents covers all such alternatives, modifications, additions, and / or rearrangements. Is considered.

  The appended claims are not expressly stated in a particular claim with the phrase “means for” and / or “step for” as a means plus function limitation It is not to be construed as including such limitation. Dependent embodiments of the present invention are detailed in the appended independent claims and their equivalents. Particular embodiments of the present invention are distinguished from one another by the attached independent claims and the equivalents.

  (References)

FIG. 1 is a conventional direct digital holography device, appropriately labeled “prior art”. FIG. 2 shows a schematic diagram of an off-axis illumination direct digital holography device (interferometer) in an on-axis position that represents an embodiment of the present invention. FIG. 3 shows a schematic diagram of the off-axis illumination direct digital holography device (interferometer) of FIG. 2 in the off-axis position. FIG. 4 shows a schematic diagram of an off-axis illumination direct digital holography device (interferometer) with multiple illumination sources that represents an embodiment of the present invention.

Claims (20)

A method of recording a plurality of off-axis illuminated spatial heterodyne holograms, each off-axis illuminated spatial heterodyne hologram including a spatial heterodyne fringe for Fourier analysis,
Digitally recording a first off-axis object illuminated spatial heterodyne hologram including a spatial heterodyne fringe for Fourier analysis using a first illumination source of the interferometer;
Digitally recording a second off-axis object illuminated spatial heterodyne hologram including a spatial heterodyne fringe for Fourier analysis using a second illumination source of the interferometer. Using a first illumination source of an interferometer to digitally record a first off-axis object illuminated spatial heterodyne hologram including a spatial heterodyne fringe for Fourier analysis, the object beam is defined by a focusing lens The object beam is diffracted by the object objective lens before being reflected from the object at an angle with respect to the measured optical axis, and the object beam is separated from the object at an angle with respect to the optical axis defined by the focusing lens. Diffracting the object beam by an object objective lens after reflecting,
Using a second illumination source of the interferometer to digitally record a second off-axis object illuminated spatial heterodyne hologram including a spatial heterodyne fringe for Fourier analysis, the object beam is defined by a focusing lens. The object beam is diffracted by the object objective lens before being reflected from the object at an angle with respect to the measured optical axis, and the object beam is separated from the object at an angle with respect to the optical axis defined by the focusing lens. The method of claim 1, comprising diffracting an object beam by an object objective lens after reflecting. Convert the axis of the first recorded off-axis object illuminated spatial heterodyne hologram containing the spatial heterodyne fringe to Fourier space and position it at the top of the heterodyne carrier frequency defined as the angle between the reference beam and the object beam By doing a Fourier analysis of the first recorded off-axis object illuminated spatial heterodyne hologram containing a spatial heterodyne fringe, and a digital filter to cut off the signal around the original origin Applying, and then performing an inverse Fourier transform,
Convert the axis of the second recorded off-axis object illuminated spatial heterodyne hologram containing the spatial heterodyne fringe to Fourier space and position it at the top of the heterodyne carrier frequency defined as the angle between the reference beam and the object beam By doing a Fourier analysis of the second recorded off-axis object illuminated spatial heterodyne hologram containing the spatial heterodyne fringe, and a digital filter to cut off the signal around the original origin The method of claim 1, further comprising applying and then performing an inverse Fourier transform.   A first Fourier analyzed off-axis object illuminated space heterodyne hologram is fused with a second Fourier analyzed off-axis object illuminated space heterodyne hologram to compute a single reconstructed image. The method of claim 3 further comprising:   The method of claim 4, further comprising reproducing a single composite image.   The method of claim 4, further comprising transmitting a single composite image.   Storing a first off-axis object illuminated spatial heterodyne hologram including a spatial heterodyne fringe for Fourier analysis as digital data; and a second off-axis object illuminated including a spatial heterodyne fringe for Fourier analysis 2. The method of claim 1, further comprising storing the spatial heterodyne hologram as digital data.   A computer program comprising computer or machine readable program elements convertible to perform the method of claim 1.   A machine readable medium comprising data generated by the method of claim 1. An apparatus operable to digitally record a plurality of off-axis illuminated spatial heterodyne holograms including spatial heterodyne fringes for Fourier analysis,
Multiple illumination sources;
A beam splitter optically coupled to a plurality of illumination sources;
A reference beam mirror optically coupled to the beam splitter;
A focusing lens optically coupled to a reference beam mirror;
A digital recorder optically coupled to a focusing lens;
A computer that performs a Fourier transform, applies a digital filter, and performs an inverse Fourier transform,
The reference beam is incident on the reference beam mirror at a non-standard angle, the object beam is incident on the object at an angle with respect to the optical axis defined by the focusing lens, and the reference beam and the object beam are focused by the focusing lens on the digital recorder. An off-axis illuminated spatial heterodyne hologram containing spatial heterodyne fringes for Fourier analysis focused on a surface and recorded by a digital recorder is formed, and the computer records a recorded off-axis illuminated spatial heterodyne containing spatial heterodyne fringes The hologram axis is transformed into Fourier space so that it is located at the upper end of the heterodyne carrier frequency defined by the angle between the reference beam and the object beam, and the signal around the original origin is transformed before performing the inverse Fourier transform. A device that cuts off.   The apparatus of claim 10, further comprising an object objective lens optically coupled between the beam splitter and the object.   The apparatus of claim 17, wherein each of the plurality of illumination sources includes a laser.   The apparatus of claim 10, wherein each of the plurality of illumination sources is switchably controlled by a computer.   The apparatus of claim 10, wherein the plurality of illumination sources are movable relative to the beam splitter.   The apparatus of claim 17, wherein the beam splitter, the reference beam mirror, and the digital recorder define a Michelson shape.   The apparatus of claim 17, wherein the beam splitter, the reference beam mirror, and the digital recorder define a Mach-Zehnder shape.   The apparatus of claim 17, further comprising a digital storage medium coupled to a computer for performing a Fourier transform, applying a digital filter, and performing an inverse Fourier transform.   11. The apparatus of claim 10, wherein the digital recorder includes a CCD camera that defines pixels.   The angle between the reference beam and the object beam and the magnification given by the focusing lens are chosen so that the digital recorder resolves the features of the off-axis illuminated spatial heterodyne hologram including the spatial heterodyne fringe for Fourier analysis, 19. The apparatus of claim 18, wherein two fringes are provided having two pixels per fringe.   A machine readable medium comprising data generated using the apparatus of claim 10.

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