(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2012/0140243 A1
`
` Colonna de Lega (43) Pub. Date: Jun. 7, 2012
`
`
`US 20120140243A1
`
`(54) NON-CONTACT SURFACE
`CHARACTERIZATION USING MODULATED
`ILLUMINATION
`
`(75)
`
`Inventor:
`
`Xavier M. Colonna de Lega,
`Middlefield, CT (US)
`
`(73) Assignee:
`
`Zygo Corporation, Middfield, CT
`(US)
`
`(21) Appl. NO’:
`
`13/309’244
`
`(22)
`
`Filed:
`
`Dec. 1, 2011
`
`Related US. Application Data
`
`(60) Provisional application No. 61/419,386, filed on Dec.
`3, 2010.
`
`Publication Classification
`
`(51)
`
`Int Cl
`(2006.01)
`G013 11/24
`(52) US. Cl. ........................................................ 356/609
`
`ABSTRACT
`(57)
`Methods for forming a three-dimensional image of a test
`object include directing light to a surface of best-focus of an
`imaging optic, where the light has an intensity modulation in
`at least one direction in the surface of best-focus, seaming a
`test object relative to the imaging optic so that a surface ofthe
`measurement object passes through the surface ofbest-focus
`of the imaging optic as the test object is scanned, acquiring,
`for each of a series of positions of the test object during the
`scan, a single image of the measurement object using the
`imaging optic, in which the intensity modulation of the light
`in the surface ofbest-focus is different for successive images,
`and forming a three-dimensional image of the test object
`based on the acquired images.
`
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`US 2012/0140243 A1
`
`Jun. 7, 2012
`
`NON-CONTAC T SURFACE
`CHARACTERIZATION USING MODULATED
`ILLUMINATION
`
`CROSS REFERENCE TO RELATED
`APPLICATIONS
`
`[0001] This application claims benefit ofprovisional patent
`application No. 61/419,386, entitled “Non-Contact Surface
`Characterization Using Modulated Illumination,” filed on
`Dec. 3, 2010, the entire contents of which are hereby incor-
`porated by reference.
`
`TECHNICAL FIELD
`
`[0002] This disclosure relates to methods of non-contact
`surface characterization using modulated illumination and
`devices configured to perform the same.
`
`BACKGROUND
`
`[0003] The field of non-contact surface characterization
`includes characterization and/or measurement of information
`
`about an object’s surface including, for example, shape and
`surface finish measurements. Tools capable of non-contact
`surface characterization can be useful in manufacturing dur-
`ing stages such as process development, quality control and
`process control on the production floor. Non-contact surface
`characterization methods can include obtaining information
`about the three-dimensional (3D) shape and location of an
`object by analyzing the frequency content of an image of the
`object in an optical system.
`
`SUMMARY
`
`In general, the subject matter described in this speci-
`[0004]
`fication relates to methods and systems for obtaining infor-
`mation about a surface of an object. The methods disclosed
`can include, for example, directing a structured illumination
`pattern to a surface of best-focus of an imaging optic while
`imaging a field in the surface of best-focus onto a multi-
`element detector. A structured illumination pattern is a non-
`uniform illumination pattem that contains some form of
`encoding based on light intensity. Examples of structured
`illumination patterns include periodic intensity patterns (e.g.,
`modulated in one or two dimensions). An object is scanned
`through the surface of best-focus while a series of images of
`the illumination patterns on the object surface are sequen-
`tially acquired by the multi-element detector. For each suc-
`cessive image obtained, the illumination pattern is modified
`so that its intensity at each point in the field corresponding to
`a detector element is modulated from one frame to the next.
`
`The resulting signal acquired at each detector element has a
`modulation, with the maximum amplitude occurring at or
`near the position of the object surface as it intersects the
`surface ofbest-focus ofthe objective. Based on an analysis of
`the signals provided by the sequence of images, measure-
`ments of topography and surface texture of the object can be
`obtained and, in some implementations, a three-dimensional
`image of the object’s surface can be produced.
`[0005]
`In some embodiments, a detector plane and pattem-
`generating plane are mapped onto a surface in object space
`that is nominally conformal to the shape of the object to be
`characterized including, for example, a plane, a sphere, a
`parabola, a cylinder, a cone, or an aspheric optic.
`[0006]
`In certain embodiments, the signal recorded at a
`pixel (i.e., element) on the detector has a modulation envelope
`
`that emulates some of the characteristics of a scanning low-
`coherence interferometer (SWLI) signal. Conversion of scan
`data to topography or reflectivity data may therefore be
`accomplished by application of envelope-detection algo-
`rithms developed for SWLI such as a frequency domain
`analysis (“FDA”) or least squares analysis (“LSQ”).
`[0007]
`In some embodiments, the device used for creating
`the projected illumination pattern is programmable, which
`allows adapting the frequency content, orientation and spatial
`intensity distribution to optimize the measurement capability
`for a given object.
`[0008] The structured illumination modulation scheme can
`be optimized to enable a fast autofocus scan of an optical
`system. An application in the context of laser eye surgery is
`the localization of the position of laser optics with respect to
`a critical component that makes contact with the cornea.
`Another application is rapid focusing of a low-coherence
`interferometer,
`in which case the autofocus scan rate is
`selected to average out the interference signal from the
`detected signal.
`[0009]
`In certain embodiments, the apparatus presents to
`the user an enhanced image ofthe object that combines height
`information with additional surface information, such as
`color, absorption, texture, etc.
`[0010] Various aspects of the subject matter described in
`this specification are summarized as follows.
`[0011]
`In general, one aspect of the subject matter
`described in this specification can be embodied in methods
`for forming a three-dimensional image of a test object, in
`which the methods include directing light to a surface of
`best-focus of an imaging optic, where the light has an inten-
`sity modulation in at least one direction in the surface of
`best-focus, scanning a test object relative to the imaging optic
`so that a surface ofthe measurement object passes through the
`surface of best-focus of the imaging optic as the test object is
`scanned, acquiring, for each of a series ofpositions ofthe test
`object during the scan, a single image of the measurement
`object using the imaging optic, in which the intensity modu-
`lation of the light in the surface of best-focus is different for
`successive images, and forming a three-dimensional image of
`the test object based on the acquired images.
`[0012] These and other embodiments can each optionally
`include one or more ofthe following features. For example, in
`some implementations, directing the light to the surface of
`best-focus includes imaging a spatial light modulator (SLM)
`to the surface of best-focus. The intensity modulation of the
`light in the surface of best-focus can be varied using the
`spatial light modulator.
`[0013]
`In some implementations, directing the light to the
`surface of best-focus includes imaging a pattem-generating
`plane onto a surface in object space. The surface can be
`conformal to a shape of the test object. The shape of the test
`object can be planar, spherical, parabolic, cylindrical, coni-
`cal, or aspheric.
`[0014]
`In some implementations, the intensity modulation
`is a periodic modulation. The periodic modulation can be a
`sinusoidal modulation. The phase of the periodic modulation
`can be varied by less than 231 between each successive image.
`The phase of the periodic modulation can be varied by at or
`less between each successive image. The phase of the peri-
`odic modulation can be varied by 313/2 between each succes-
`sive image.
`[0015]
`In some implementations, the intensity modulation
`is a two-dimensional intensity modulation. The scan posi-
`
`0020
`
`0020
`
`

`

`US 2012/0140243 A1
`
`Jun. 7, 2012
`
`tions can be evenly spaced. The intensity modulation can be
`selected based on a slope of the test object surface.
`[0016]
`In some implementations, forming the three-dimen-
`sional image includes identifying, for multiple different loca-
`tions of the test object surface, the scan position correspond-
`ing to where each location intersects the surface ofbest-focus.
`An intensity of the acquired images as a function of scan
`position at each of the different locations can include an
`amplitude modulation. Identifying the scan position corre-
`sponding to where each location intersects the surface of
`best-focus can include identifying the scan position where a
`modulation amplitude is largest.
`[0017]
`In some implementations, forming the three-dimen-
`sional image includes deriving an intensity signal for each of
`multiple different locations of the test object surface, each
`intensity signal corresponding to the intensity of the acquired
`images at the corresponding location as a function of scan
`position. Forming the three-dimensional image can include
`identifying a scan position corresponding to a maximum
`amplitude of a modulation of the intensity signal for each
`location. Identifying the scan position can include transform-
`ing each intensity signal into a frequency domain.
`[0018]
`In some implementations, the test object is a lens
`element. The three-dimensional image can be, for example, a
`monochrome image. Alternatively,
`the three-dimensional
`image can be a color image.
`[0019]
`In general, another aspect of the subject matter
`described in this specification can be embodied in methods
`for forming a three-dimensional image of a test object, in
`which the methods each include forming an image of a spatial
`light modulator at a surface ofbest-focus of an imaging optic,
`scanning a test object relative to the imaging optic so that a
`surface ofthe measurement object passes through a surface of
`best-focus of the imaging optic as the test object is scanned,
`acquiring, for each of a series of positions of the test object
`during the scan, a single image of the test object using the
`imaging optic, in which the spatial light modulator varies an
`intensity modulation in the light forming the image so that the
`modulation ofthe light at the surface ofbest-focus is different
`for successive images, and forming a three-dimensional
`image of the test object based on the acquired images.
`[0020]
`In general, another aspect of the subject matter
`described in this specification can be embodied in methods
`for forming a three-dimensional image of a test object, in
`which the methods each include directing light to a surface of
`best-focus of an imaging optic, where the light has an inten-
`sity modulation in at least one direction in the surface of
`best-focus, scanning a test object relative to the imaging optic
`so that a surface of the measurement object passes through a
`surface of best-focus of the imaging optic as the test object is
`scanned, imaging the surface ofbest-focus to a multi-element
`detector, acquiring, for each of a series of positions of the test
`object during the scan, a single intensity measurement at one
`or more elements of the multi-element detector, in which the
`intensity modulation ofthe light in the surface ofbest-focus is
`different for successive positions of the test object during the
`scan, and forming a three-dimensional image of the test
`object based on the acquired intensity measurements.
`[0021]
`In general, another aspect of the subject matter
`described in this specification can be embodied in systems for
`forming a three-dimensional image of a test object, in which
`the systems each include a microscope including an imaging
`optic, the imaging optic having a surface of best-focus, a
`spatial
`light modulator, one or more optical elements
`
`arranged to direct light from the spatial light modulator to
`form an image of the SLM at the surface of best-focus during
`operation ofthe system, a scanning stage arranged to scan the
`test object relative to the microscope object during operation
`of the system so that a surface of the test object intersects the
`surface of best-focus, a multi-element detector positioned
`relative to the microscope such that the microscope forms an
`image of a field at the surface of best-focus on the multi-
`element detector during operation of the system, and an elec-
`tronic control module in communication with the scanning
`stage,
`the spatial
`light modulator, and the multi-element
`detector, in which during operation, the system causes the
`multi-element detector to acquire a single image of the test
`object for each of multiple scan positions of the test object
`relative to the imaging optic, causes the SLM to variably
`modulate the intensity of light at the surface of best-focus in
`at least one direction so that the intensity modulation of the
`light is different for successive images, and forms a three-
`dimensional image of the test object based on the acquired
`images.
`[0022] This and other embodiments can each optionally
`include one or more of the following features. In some imple-
`mentations, the system includes, for example, a light source
`arranged to direct light to the SLM during operation of the
`system. The SLM can be a reflective SLM or a transmissive
`SLM.
`
`In some implementations, the SLM can be a liquid
`[0023]
`crystal panel, or include a micro-mirror array.
`[0024]
`In some implementations, the imaging optic has a
`numerical aperture greater than 0.6, a numerical aperture
`greater than 0.8, a numerical aperture greater than 0.9, or a
`numerical aperture of 0.95.
`the system further
`[0025]
`In some implementations,
`includes color filters arranged to filter the wavelength of light
`forming the images at the multi-element detector.
`[0026] The one or more optical elements can include, for
`example, a fisheye lens, an endoscope, and/or a zoom lens.
`[0027]
`Implementations disclosed herein can offer several
`advantages. For example,
`in some implementations,
`the
`methods and apparatus can be used to provide non-contact
`three-dimensional imaging of an object. The imaging can be
`performed using short measurement times and/or to achieve
`high resolution images of objects’ surfaces. In some imple-
`mentations, the imaging is performed with reduced sensitiv-
`ity to environmental perturbations such as, for example,
`vibration or acoustic noise.
`
`Implementations offer other advantages as well. For
`[0028]
`example, the methods and structures disclosed herein can, in
`some implementations, provide similar depth sectioning
`capabilities as a conventional confocal microscope. The use
`of structured illumination profiling can offer certain benefits
`compared to confocal microscopy (e.g., reduced source
`brightness requirements) and interference microscopy. For
`example, in some implementations, structured illumination
`has reduced source brightness requirements relative to con-
`ventional interference microscopes. Alternatively, or in addi-
`tion, restrictions on which non-interferometric microscope
`objectives can be used can be reduced. For example, in some
`implementations, higher numerical aperture objectives are
`available relative to the objectives available in Michelson or
`Mirau interferometers.
`
`[0029] The details of one or more embodiments are set
`forth in the accompanying drawings and the description
`
`0021
`
`0021
`
`

`

`US 2012/0140243 A1
`
`Jun. 7, 2012
`
`below. Other features and advantages will be apparent from
`the description, drawings, and from the claims.
`
`BRIEF DESCRIPTION OF DRAWINGS
`
`FIG. 1 is a schematic diagram of an exemplary sys-
`[0030]
`tem for providing a 3D image of a sample object.
`[0031]
`FIG. 2 is a schematic diagram of an exemplary sys-
`tem for providing a 3D image of a sample object.
`[0032]
`FIG. 3 is a schematic illustrating various scan posi-
`tions of a sample object.
`[0033]
`FIG. 4 is a graph ofa simulated light intensity signal.
`[0034]
`FIG. 5 is a graph of an experimental intensity signal
`recorded by a pixel of an image-recording device.
`[0035]
`FIG. 6 is an exemplary topography map ofa l3-um
`step height step generated by FDA processing of light inten-
`sity signals.
`[0036]
`FIG. 7 is a graph of a simulated intensity signal.
`[0037]
`FIGS. 8A-8B are plots of a simulated analog inten-
`sity signal overlaid with a corresponding digitized sampling
`of the intensity signal.
`[0038]
`FIG. 8C is a plot of the simulated analog intensity
`signal of FIG. 8B overlaid with the corresponding digitized
`intensity signal of FIG. 8B, where zeros have been inserted
`into the digitized intensity signal.
`[0039]
`FIG. 9A is a plot of the magnitude of the digitized
`sample signal from FIG. 8A and the phase of the digitized
`intensity signal from FIG. 8C.
`[0040]
`FIG. 9B is a plot ofthe phase ofthe digitized sample
`signal from FIG. 8A and the magnitude of the digitized inten-
`sity signal from FIG. 8C.
`[0041]
`FIG. 10A is a plot of a simulated analog intensity
`signal overlaid with a corresponding digitized sampling ofthe
`simulated intensity signal.
`[0042]
`FIG. 10B is a plot of the simulated analog intensity
`signal of FIG. 10A overlaid with the digitized intensity signal
`of FIG. 10A, where zero values have been inserted into the
`digitized intensity signal.
`[0043]
`FIGS. 11-13 are exemplary images of a microlens
`onto which an illumination pattern is projected.
`[0044]
`FIG. 14 is a schematic diagram of an exemplary
`structured illumination imaging system.
`[0045]
`FIG. 15 is a schematic diagram of an exemplary
`imaging system.
`[0046]
`FIG. 16 is a schematic diagram of an exemplary
`imaging system.
`[0047]
`FIGS. 17A-17B are schematic diagrams of exem-
`plary imaging systems.
`[0048]
`FIGS. 18A-18B are schematic diagrams of exem-
`plary imaging systems.
`[0049]
`FIG. 19A is a 3D graph of experimental topography
`data collected on a sample object.
`[0050]
`FIG. 19B is a color image of the surface of the
`sample object of FIG. 19A.
`[0051]
`FIG. 19C is an exemplary color image produced by
`combining the topographical data of FIG. 19A with the color
`image of FIG. 19B.
`[0052]
`FIG. 20 is a schematic of an exemplary system for
`performing laser eye surgery.
`
`DETAILED DESCRIPTION
`
`Acquiring the Light Intensity Signal
`[0053]
`FIG. 1 is a schematic diagram of an exemplary
`structured illumination system 100 for providing a 3D image
`
`of a sample object 102. An illumination portion 103 of the
`system 100 includes an illumination source 104, a spatial
`light modulator (SLM) 106, one or more lenses (108a-108c),
`an aperture 110 and a beam combiner 112. An imaging por-
`tion 105 of the system 100 includes an image-recording
`device 114, a beam splitter 116, an objective lens 118 and a
`tube lens 120. For the purposes of this disclosure, the coor-
`dinate system is defined such that the z-axis is parallel to the
`optical axis of the objective lens 118 and the x and y-axes are
`parallel to the lens’ plane ofbest-focus such that xyz forms an
`orthogonal coordinate system.
`[0054] During operation of the system 100, light 101 gen-
`erated from the illumination source 104 passes through the
`lenses 108a, 1081) and the aperture 110, where the light 101
`then is incident on the beam splitter 112. Beam splitter 112
`reflects a portion of the incident light 101 onto the SLM 106.
`In the present example, the SLM 106 is configured to modify
`and reflect the light incident on its surface so as to produce an
`illumination pattern characterized as either binary (i.e., the
`imaging pattern has regions where light is present and regions
`where light is absent) or quasi-continuous (i.e., the imaging
`pattern can be approximated by continuous varying levels of
`light intensity).
`[0055] The illumination pattern reflected from the SLM
`106 then passes through the beam splitter 112 and lens 108c
`to a second beam splitter 116 where the illumination pattern
`then is directed through the objective lens 118 and preferen-
`tially fills the back pupil of the objective 118. The illumina-
`tion pattern is re-imaged in object space to the plane of best-
`focus (focal plane) of the objective lens 118. Light reflecting
`and/or scattering off a surface of the sample object 102 then
`proceeds through the objective lens 118, the beam splitter
`116, and the tube lens 120 onto a light-detecting surface/plane
`of the image-recording device 114 where it is recorded. The
`recorded light thus acquired can be stored in digital format as
`an array of light intensity signals, with each light intensity
`signal being acquired from a corresponding pixel of the
`image-recording device 114.
`[0056] During imaging, the object 102 is translated verti-
`cally with respect to the objective lens 118 (i.e., toward or
`away from the objective lens 118). The sample object 102 can
`be displaced or actuated by an electromechanical transducer
`(not shown) and associated drive electronics controlled by a
`computer 122 so as to enable precise scans along a direction
`of translation of the object 102. Examples of transducers
`include, but are not
`limited to, piezoelectric transducers
`(PZT), stepper motors and voice coils. Alternatively, or in
`addition, the objective lens 118 may be translated vertically
`with respect to a position of the sample object 102. Again, an
`electromechanical transducer and associated drive electron-
`
`ics may be used to control the translation. The image-record-
`ing device 114 simultaneously records imaging data as the
`object 102 is scanned through the plane of best-focus of the
`objective lens 118 such that multiple light intensity signals
`will be recorded over time. That is, an image ofthe object and
`illumination pattern is captured by the image-recording
`device in the form of the light intensity signal at correspond-
`ing scan positions. For example, if the image-recording
`device 114 includes a 128x128 array of pixels and if 64
`images are stored during a scan, then there will be approxi-
`mately 16,000 light intensity signals each 64 data points in
`length. In some implementations,
`the scan positions are
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`evenly spaced, i.e., the translation distance between succes-
`sive images captured by the image-recording device is the
`same.
`
`Furthermore, the SLM 106 spatially modulates the
`[0057]
`illumination pattern as the sample object 102 is translated,
`such that the object 102 is illuminated with a different pattern
`at different corresponding vertical positions of the scan. The
`continuous modification of the illumination pattern during
`the scan results in a modulated light intensity signal at each
`pixel of the image-recording device 114. After the data has
`been acquired, the computer 122 can process the light inten-
`sity signals in accordance with, for example, pattern match-
`ing techniques, and output data indicative of a surface topog-
`raphy of the sample object 102.
`[0058] When a surface of the sample object 102 is located
`at the plane of best-focus of the objective 118, an in-focus
`image ofthe illumination pattern is formed on a surface ofthe
`object 102. The in-focus image exhibits the highest contrast
`achievable for a given illumination numerical aperture (NA)
`of the system 100. The intensity of the image of the object
`surface that is reflected back to the image-recording device
`114 at each pixel is proportional to the product of the local
`object surface reflectivity and the local intensity of the pro-
`jected illumination pattern. In contrast, when the surface of
`the object 102 is located away from the plane ofbest-focus of
`the objective lens 118, the image of the illumination pattern
`on the surface of the object 102 is blurred and thus exhibits
`reduced contrast. The image of the surface of the object 102
`passing back through the objective lens 118 towards the
`image-recording device then is blurred again. The result is
`that the contrast of the projected illumination pattern, as seen
`on the image-recording device, is a function of the vertical
`displacement ofthe object surface with respect to the plane of
`best-focus of the objective. Accordingly, the depth profiling
`capability of the system 100 arises from the detection of the
`position of the object 102 for which the pattern contrast is a
`maximum at each pixel ofthe image-recording device 114, as
`the object 102 is scanned through the best-focus plane.
`[0059]
`In some implementations, the SLM 106 can be used
`in a transmission arrangement as opposed to reflection. For
`example, FIG. 2 shows an exemplary system 200 that
`includes the same components as system 100, except that a
`single beam splitter 216 is used in the arrangement and a SLM
`is configured to transmit incident light rather than reflect the
`incident light (computer 122 also is omitted for ease of view-
`ing). In the example shown in FIG. 2, the transmission SLM
`206 modifies incident light 201 generated by an illumination
`source 204 to produce a binary or quasi-continuous illumina-
`tion pattern. The illumination pattern produced by the SLM
`206 passes through a lens 208c and is incident on the beam
`splitter 216, where the pattern then is directed through an
`objective lens 218 and imaged onto a plane ofbest-focus for
`the objective. The illumination pattern reflects off a sample
`object 202 and passes back through the objective lens 218, the
`beam splitter 216, a tube lens 220 and is finally detected by a
`image-recording device 214. Similar to the system 100, the
`illumination pattern produced by the SLM 206 can be spa-
`tially modulated as the image data is acquired, such that
`different light intensity patterns are produced at correspond-
`ing different scan positions of the object.
`[0060]
`In each of the foregoing examples, the illumination
`sources 104, 204 can include, but are not limited to, spec-
`trally-broadband sources or narrow band sources. Examples
`of broadband sources include: an incandescent source, such
`
`as a halogen bulb or metal halide lamp, with or without
`spectral bandpass filters; a broadband laser diode; a light-
`emitting diode; a combination of several light sources of the
`same or different types; an arc lamp; any source in the visible
`spectral region (about 400 to 700 nm), any source in the IR
`spectral region (about 0.7 to 300 um), any source in the UV
`spectral region (about 10 to 400 nm). For broadband applica-
`tions, the source preferably has a net spectral bandwidth
`broader than 5% of the mean wavelength, or more preferably
`greater than 10%, 20%, 30%, or even 50% ofthe mean wave-
`length. The source may also include one or more diffuser
`elements to increase the spatial extent of the input light being
`emitted from the source. Examples of narrow band sources
`include a laser or a broadband source in combination with a
`narrowband filter.
`
`[0061] The source can be a spatially-extended source or a
`point source. In some implementations, it is preferable to use
`a spatially-extended source (e.g., when the surface of an
`object being imaged is smooth) to avoid observing a high-
`contrast pattern regardless of the position of the object with
`respect to the plane of best focus. The image-recording
`devices 114, 214 can include a plurality of detector elements,
`e.g., pixels, arranged in at least one and more generally two
`dimensions. Examples of image-recording devices include
`digital cameras, multi-element charge coupled devices
`(CCDs) and complementary metal oxide semiconductor
`(CMOS) detectors. Other image-recording devices may be
`used as well. In some implementations, one or more color
`filters can be included in the system to filter the wavelength of
`light forming the images at the image-recording device. The
`one or more color filters can be arranged to be an integral
`component ofthe image-recording device or as separate from
`the image-recording device.
`[0062]
`In some implementations, the objective lenses 118,
`218 can be incorporated as components of any standard
`microscope. For example, the systems can include a micro-
`scope configured for use with one or more different objective
`lenses, each providing a different magnification. The NA of
`the objective lenses 118, 218 can be about 0.1 or greater (e.g.,
`about 0.2 or greater, about 0.3 or greater, about 0.4 or greater,
`about 0.5 or greater, about 0.6 or greater, about 0.7 or greater,
`about 0.8 or greater, about 0.9 or greater, or about 0.95 or
`greater). Other NA values are possible as well.
`[0063] Examples of SLMs that can be used to reflect light,
`similar to the arrangement shown in FIG. 1, include liquid
`crystal on silicon (LCOS) devices or micromirror array
`devices, e.g., a digital micromirror device (DMD). To spa-
`tially modulate illumination patterns produced by a LCOS
`device, a user can electronically control, using the appropriate
`hardware and software, the direction and amount of light
`reflected by each pixel of the LCOS device. Likewise, to
`spatially modulate the illumination pattern produced by a
`DMD, a user can electronically control the direction and/or
`orientation of each individual mirror to vary the amount of
`light reflected at each mirror. Examples of SLMs that can be
`used to transmit light, similar to the arrangement shown in
`FIG. 2 include liquid crystal device (LCD) modulators that
`can be electronically controlled to vary the amount of light
`transmitted. Alternatively, in some implementations, trans-
`mission SLMs can include intensity masks, such as gratings,
`Ronchi rulings, or other patterned surfaces that have regions
`of varying degrees of absorption for the wavelength of inci-
`dent light. To spatially modulate the illumination patterns
`produced by the transmission SLMs formed from intensity
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`masks, the SLMs can be mounted on a mechanical frame that
`provides controlled in-plane motion of the SLM. The motion
`ofthe frame can be provided using one or more mechanical or
`electronic actuators, including, for example, piezoelectric
`actuators, stepper-motors, or voice coils. Other SLMs can be
`used in transmission