Patent ID: 12244116

Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings. It is noted that the invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to persons skilled in the relevant art based on the teachings contained herein.

DETAILED DESCRIPTION

This specification discloses one or more embodiments that incorporate the features of this invention. The disclosed embodiment(s) merely exemplify the present invention. The scope of the present invention is not limited to the disclosed embodiment(s). The present invention is defined by the claims appended hereto.

The embodiment(s) described, and references in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, “an exemplary embodiment”, etc., indicate that the embodiment(s) described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is understood that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “on,” “upper,” “left,” “right” and the like, may be used herein for ease of description to describe one element's or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

Before describing specific embodiments in more detail, it is instructive to present an example environment in which embodiments of the present invention may be implemented. Referring toFIG.1, a photolithography system100includes an illumination system105. As described more fully below, the illumination system105includes a light source that produces a pulsed light beam110and directs it to a photolithography exposure apparatus or scanner115that patterns microelectronic features on a wafer120. The wafer120is placed on a wafer table125constructed to hold wafer120and connected to a positioner (not shown) configured to accurately position the wafer120in accordance with certain parameters.

The photolithography system100uses a light beam110having a wavelength in the deep ultraviolet (DUV) range, for example, with wavelengths of 248 nanometers (nm) or 193 nm. The minimum size of the microelectronic features that can be patterned on the wafer120depends on the wavelength of the light beam110, with a lower wavelength permitting a smaller minimum feature size. When the wavelength of the light beam110is 248 nm or 193 nm, the minimum size of the microelectronic features can be, for example, 50 nm or less. The bandwidth of the light beam110can be the actual, instantaneous bandwidth of its optical spectrum (or emission spectrum), which contains information on how the optical energy of the light beam110is distributed over different wavelengths. The scanner115includes an optical arrangement having, for example, one or more condenser lenses, a mask, and an objective arrangement. The mask is movable along one or more directions, such as along an optical axis of the light beam110or in a plane that is perpendicular to the optical axis. The objective arrangement includes a projection lens and enables the image transfer to occur from the mask to the photoresist on the wafer120. The illumination system105adjusts the range of angles for the light beam110impinging on the mask. The illumination system105also homogenizes (makes uniform) the intensity distribution of the light beam110across the mask.

The scanner115can include, among other features, a lithography controller130, air conditioning devices, and power supplies for the various electrical components. The lithography controller130controls how layers are printed on the wafer120. The lithography controller130includes a memory that stores information such as process recipes. A process program or recipe determines the length of the exposure on the wafer120based on, for example, the mask used as well as other factors that affect the exposure. During lithography, a plurality of pulses of the light beam110illuminate the same area of the wafer120to constitute an illumination dose.

The photolithography system100also preferably includes a control system135. In general, the control system135includes one or more of digital electronic circuitry, computer hardware, firmware, and software. The control system135also includes memory which can be read-only memory and/or random access memory. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including, by way of example, semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM disks.

The control system135can also include one or more input devices (such as a keyboard, touch screen, microphone, mouse, hand-held input device, etc.) and one or more output devices (such as a speaker or a monitor). The control system135may also include one or more programmable processors, and one or more computer program products tangibly embodied in a machine-readable storage device for execution by one or more programmable processors. The one or more programmable processors can each execute a program of instructions to perform desired functions by operating on input data and generating appropriate output. Generally, the processors receive instructions and data from the memory. Any of the foregoing may be supplemented by, or incorporated in, specially designed ASICs (application-specific integrated circuits). The control system135can be centralized or be partially or wholly distributed throughout the photolithography system100.

Referring toFIG.2, an exemplary laser source system within the illumination system105is a pulsed laser source that produces a pulsed laser beam as the light beam110.FIG.2shows illustratively and in block diagram a gas discharge laser system according to an embodiment of certain aspects of the disclosed subject matter. The gas discharge laser system may include, e.g., a solid state or gas discharge seed laser system140, an amplification stage, e.g., a power ring amplifier (“PRA”) stage145, relay optics150and laser system output subsystem160. The seed system140may include, e.g., a master oscillator (“MO”) chamber165.

The seed laser system140may also include a master oscillator output coupler (“MO OC”)175, which may comprise a partially reflective mirror, forming with a reflective grating (not shown) in a line narrowing module (“LNM”)170, an oscillator cavity in which the seed laser140oscillates to form the seed laser output pulse, i.e., forming a master oscillator (“MO”). The system may also include a line-center analysis module (“LAM”)180. The LAM180may include an etalon spectrometer for fine wavelength measurement and a coarser resolution grating spectrometer. A MO wavefront engineering box (“WEB”)185may serve to redirect the output of the MO seed laser system140toward the amplification stage145, and may include, e.g., beam expansion with, e.g., a multi prism beam expander (not shown) and coherence busting, e.g., in the form of an optical delay path (not shown).

The amplification stage145may include, e.g., a PRA lasing chamber200, which may also be an oscillator, e.g., formed by seed beam injection and output coupling optics (not shown) that may be incorporated into a PRA WEB210and may be redirected back through the gain medium in the chamber200by a beam reverser220. The PRA WEB210may incorporate a partially reflective input/output coupler (not shown) and a maximally reflective mirror for the nominal operating wavelength (e.g., at around 193 nm for an ArF system) and one or more prisms.

A bandwidth analysis module (“BAM”)230at the output of the amplification stage145may receive the output laser light beam of pulses from the amplification stage and pick off a portion of the light beam for metrology purposes, e.g., to measure the output bandwidth and pulse energy. The laser output light beam of pulses then passes through an optical pulse stretcher (“OPuS”)240and an output combined autoshutter metrology module (“CASMM”)250, which may also be the location of a pulse energy meter. One purpose of the OPuS240may be, e.g., to convert a single output laser pulse into a pulse train. Secondary pulses created from the original single output pulse may be delayed with respect to each other. By distributing the original laser pulse energy into a train of secondary pulses, the effective pulse length of the laser can be expanded and at the same time the peak pulse intensity reduced. The OPuS240can thus receive the laser beam from the PRA WEB210via the BAM230and direct the output of the OPuS240to the CASMM250. Other suitable arrangements may be used in other embodiments.

The PRA lasing chamber200and the MO165are configured as chambers in which electrical discharges between electrodes may cause lasing gas discharges in a lasing gas to create an inverted population of high energy molecules, including, e.g., Ar, Kr, and/or Xe, to produce relatively broad band radiation that may be line narrowed to a relatively very narrow bandwidth and center wavelength selected in a line narrowing module (“LNM”)170, as is known in the art.

Typically, the tuning takes place in the LNM. A typical technique used for line narrowing and tuning of lasers is to provide a window at the back of the laser's discharge cavity through which a portion of the laser beam passes into the LNM. There, the portion of the beam is expanded with a prism beam expander and directed to a grating which reflects a narrow selected portion of the laser's broader spectrum back into the discharge chamber where it is amplified. The laser is typically tuned by changing the angle at which the beam illuminates the grating using an actuator such as, for example, a piezoelectric actuator.

In operation, the OPuS240stretches the excimer or other gas discharge laser, e.g., a molecular fluorine gas discharge laser, having a given pulse duration and TIS to a longer pulse having several peaks and a larger TIS.

FIG.3is a schematic diagram of front view of an example of an optical pulse stretcher401having first optical pulse stretcher401aand second optical pulse stretcher401b, according to some embodiments of the present disclosure. The optical pulse stretcher401receives input beam pulse411and stretches it to output a stretched output beam pulse413.

According to some embodiments, and as discussed in more detail below, second optical pulse stretcher401bcan include two or more (for example, three) stages of confocal optical pulse stretchers.

In some examples, these three stages of confocal optical pulse stretcher can be positioned approximately parallel to each other in second optical pulse stretcher401b. In some embodiments, second optical pulse stretcher401bcan be positioned perpendicular or approximately perpendicular to first optical pulse stretcher401a. In other words, in some embodiments, first optical pulse stretcher401a(e.g., an orthogonal optical pulse stretcher that may be positioned vertically) is positioned perpendicular or approximately perpendicular to the two or more (for example, three) stages of confocal optical pulse stretchers of second optical pulse stretcher401bwhich is positioned vertically in the figure. According to some embodiments, second optical pulse stretcher401bis designed such that it provides additional optical delay.

According to some embodiments, the extended optical pulse stretcher401combines two or more confocal optical pulse stretchers. For example, extended optical pulse stretcher401combines confocal optical pulse stretchers in the combination of 4 reflections, 4 reflections, 12 reflections, and 12 reflections per optical circuit configuration. According to some embodiments, the inclusion of the combination of different mirror separations and delay path lengths (e.g., 4 reflections and 12 reflections delay lengths) can result in very long pulse stretching and minimal efficiency losses.

According to some embodiments, second optical pulse stretcher401bcan include three stages of confocal optical pulse stretchers. However, the embodiments of this disclosure are not limited to these examples, and second optical pulse stretcher401bcan include other numbers of stages of confocal optical pulse stretchers. In some examples, the first stage of second optical pulse stretcher401bis discussed as having two mirrors. However, the embodiments of this disclosure are not limited to these examples and the first stage of second optical pulse stretcher401bcan include other numbers (for example two or more) and/or configurations of mirrors. In some examples, the plurality of mirrors used in the first stage of second optical pulse stretcher401bare configured to generate four reflections of the laser beam between them.

In some examples, the second stage of second optical pulse stretcher401bis discussed as having four mirrors. However, the embodiments of this disclosure are not limited to these examples and the second stage of second optical pulse stretcher401bcan include other numbers (for example four or more) and/or configurations of mirrors. In some examples, the plurality of mirrors used in the second stage of second optical pulse stretcher401bare configured to generate twelve reflections of the laser beam between them.

In some examples, the third stage of second optical pulse stretcher401bis discussed as having four mirrors. However, the embodiments of this disclosure are not limited to these examples and the third stage of second optical pulse stretcher401bcan include other numbers (for example four or more) and/or configurations of mirrors. In some examples, the plurality of mirrors used in the third stage of second optical pulse stretcher401bare configured to generate twelve reflections of the laser beam between them.

According to some embodiments, first optical pulse stretcher401aand the stages of second optical pulse stretcher401bare designed such that optical delay increases from first optical pulse stretcher401ato second optical pulse stretcher401b. Also, the optical delay of each stage of second optical pulse stretcher401bincreases from the first to the third stage. For example, first optical pulse stretcher401a(e.g., the orthogonal optical pulse stretcher) can have an optical delay. The first stage of second optical pulse stretcher401bcan have a first optical delay equal to or greater than the optical delay of first optical pulse stretcher401a. The second stage of second optical pulse stretcher401bcan have a second optical delay equal to or greater than the first optical delay. The third stage of second optical pulse stretcher401bcan have a third optical delay equal to or greater than the second optical delay. According to some embodiments, the optical delay can be determined based on the distance that the beam travels within an optical pulse stretcher.

According to some embodiments, a first stage of second optical pulse stretcher401bcan have an optical design including two mirrors (e.g., two lower mirrors of mirrors501and502inFIG.3) that produce four reflections of the laser beam between them. Although this example is discussed with two mirrors, the first stage of second optical pulse stretcher401bcan include other numbers of mirrors (for example, two or more mirrors). These mirrors can be positioned to generate four reflections of the laser beam between them. In some embodiments, the two mirrors of the first stage of second optical pulse stretcher401bcan be separated from each other by a physical distance of about 2 m-4 m. For example, the physical distance can be about 2.5 m to 3.5 m. These distances are provided by way of example only and other distances can be used in other embodiments. In some examples, the first stage of second optical pulse stretcher401bcan be capable of optical pulse stretching having, from example, an optical delay of about 60 ns-80 ns. For example, an optical delay of about 65 ns-75 ns. For example, an optical delay of about 70 ns-75 ns. It is noted that the example physical distance between the two mirrors and the example optical delays provided do not limit the embodiments of this disclosure. The first stage of second optical pulse stretcher401bcan be designed such that various other physical distances and/or various optical delays are achieved.

According to some embodiments, mirrors (e.g., the two lower mirrors of mirrors501and502) of the first stage of second optical pulse stretcher401bcan include rectangular concave mirrors. For example, two large rectangular concave mirrors can be used but in other embodiments other shapes are used. According to some embodiments, the reflective surface of the mirrors can be spherically concave such that the distance between the two mirrors (e.g., the surfaces of the two lower mirrors of mirrors501and502) of the first stage of second optical pulse stretcher401bis equal to (or about equal to) the radius of the curvature of each of the two mirrors. For example, the mirrors can be designed and positioned based on a telecentric design. The concave mirrors can be designed with orthogonal tip-tilt adjustment and also Z-axis (e.g., the direction of the propagation of beam) adjustment, according to some embodiments.

According to some embodiments, the first stage of second optical pulse stretcher401bcan include additional optical elements. In one example, the first stage of second optical pulse stretcher401bcan include a beam splitter used to split the laser beam and to generate copies of the laser beam. The beam splitter of the first stage of second optical pulse stretcher401bcan have a reflectivity of, for example, about 45%-65%. In some examples, the beam splitter can have a reflectivity of about 50%-60%. But the embodiments of this disclosure are not limited to these examples and various other values of reflectivity can be used. In some examples, the reflectivity of the beam splitter can depend on and/or be calculated based on the reflectivity of the mirrors used in the first stage of second optical pulse stretcher401b.

According to some embodiments, a second stage of second optical pulse stretcher401bcan have an optical design including four mirrors (e.g., four middle mirrors of mirrors501and502inFIG.3) that produce 12 reflections of the laser beam between them. Although this example is discussed with four mirrors, the second stage of second optical pulse stretcher401bcan include other numbers of mirrors (for example, four or more mirrors). These mirrors can be positioned to generate twelve reflections of the laser beam between them. In some embodiments, the two pairs of mirrors of the second stage of second optical pulse stretcher401bcan be separated from each other by a physical distance of about 2 m-4 m. For example, the physical distance can be about 2.5 m to 3.5 m. These distances are provided by way of example only and other distances can be used in other embodiments. In some examples, the second stage of second optical pulse stretcher401bcan be capable of optical pulse stretching having, from example, an optical delay of about 170 ns-210 ns. For example, an optical delay of about 180 ns-190 ns. For example, an optical delay of about 185 ns-195 ns. It is noted that the example physical distance between the two pairs of mirrors and the example optical delays provided do not limit the embodiments of this disclosure. The second stage of second optical pulse stretcher401bcan be designed such that various other physical distances and/or various optical delays are achieved.

According to some embodiments, mirrors (e.g., the four middle mirrors of mirrors501and502) of the second stage of second optical pulse stretcher401bcan include rectangular concave mirrors. For example, four large rectangular concave mirrors can be used but in other embodiments other shapes are used. According to some embodiments, the reflective surface of the mirrors can be spherically concave such that the distance between the two pairs of mirrors (e.g., the surfaces of the two pairs of middle mirrors of mirrors501and502) of the second stage of second optical pulse stretcher401bis equal to (or about equal to) the radius of the curvature of each of the four mirrors. For example, the mirrors can be designed and positioned based on a telecentric design. The concave mirrors can be designed with orthogonal tip-tilt adjustment, according to some embodiments.

According to some embodiments, the second stage of second optical pulse stretcher401bcan include additional optical elements. In one example, the second stage of second optical pulse stretcher401bcan include a beam splitter (middle beam splitter of beam splitters503ofFIG.3) used to split the laser beam and to generate copies of the laser beam. The beam splitter of the second stage of second optical pulse stretcher401bcan have a reflectivity of, for example, about 45%-65%. In some examples, the beam splitter can have a reflectivity of about 50%-60%. But the embodiments of this disclosure are not limited to these examples and various other values of reflectivity can be used. In some examples, the reflectivity of the beam splitter can depend on and/or be calculated based on the reflectivity of the mirrors used in the second stage of second optical pulse stretcher401b.

Other details concerning optical pulse stretchers can be obtained from U.S. Pat. No. 7,369,597, titled “Laser Output Light Pulse Stretcher”, issued May 6, 2008, the entire contents of which are hereby incorporated by reference.

FIG.4illustrates a schematic view of part of the paths of laser beams in second optical pulse stretcher401b, according to some embodiments of the present disclosure.

As illustrated inFIG.4, laser beam601, which is optically stretched using the stage of first optical pulse stretcher401aenters second optical pulse stretcher401b. Using first beam splitter503a, laser beam601is split into laser beam603and laser beam605. Laser beam605enters the second stage of second optical pulse stretcher401b. Laser beam603enters the first stage of second optical pulse stretcher401b, which includes two mirrors. After four reflections from the two mirrors501a,502aof the first stage of second optical pulse stretcher401bas shown inFIG.5A, part of the laser beam enters the second stage of second optical pulse stretcher401bby reflecting off beam splitter503a, the rest of beam will continue to further loops inside the optical pulse stretcher400.

Laser beam605(and/or the laser beam from the first stage of second optical pulse stretcher401b) is split into laser beam607and laser beam609. Laser beam609enters the third stage of second optical pulse stretcher401b. Laser beam607enters the second stage of second optical pulse stretcher401b, which includes four mirrors501c,501b,502b, and501cas shown inFIG.5B. After twelve reflections from the four mirrors, as indicated by the numbers 1-12, of the second stage of second optical pulse stretcher401bpart of the laser beam enters the third stage of enters second optical pulse stretcher401bby reflecting off beam splitter503b.

Laser beam609(and/or the laser beam from the second stage of the second optical pulse stretcher401b) is split into laser beam611and laser beam613. Laser beam613is reflected using mirrors505aand505bback to first optical pulse stretcher401a. Laser beam611enters the third stage of second optical pulse stretcher401b, which includes four mirrors. After twelve reflections from the four mirrors of the third stage of second optical pulse stretcher401b, part of the laser beam is reflected toward first optical pulse stretcher401ausing beam splitter503cand fold mirrors505aand505b(FIG.4).

FIG.6illustrates a schematic view of part of the paths of laser beams in second optical pulse stretcher401band parts of mirrors used in second optical pulse stretcher401b, according to some embodiments of the present disclosure.

InFIG.6, the five mirrors on one side of second optical pulse stretcher401bare illustrated. It will be understood that according to some embodiments an almost symmetric arrangement is also present in the second optical pulse stretcher401b. In this example, mirror502aof the first stage of second optical pulse stretcher401bis illustrated. A mirror (e.g., mirror501a) is on the other side of the first stage of second optical pulse stretcher401b, which is not illustrated in this view. In this example, one pair of mirrors502band502cof the second stage of second optical pulse stretcher401bis illustrated. Another pair of mirrors (e.g., a pair of mirrors501band501c) is on the other side of the second stage of second optical pulse stretcher401b, which is not illustrated in this view. Also, in this example, one pair of mirror502dand502eof the third stage of second optical pulse stretcher401bis illustrated. Another pair of mirrors (e.g., a pair of mirrors501dand501e) is on the other side of the third stage of second optical pulse stretcher401b, which is not illustrated in this view.

The following discussion is in terms of an arrangement in which the optical components within the OPuS such as mirrors are arranged in two banks which are almost left-right symmetric with respect to a central axis for the sake of having a concrete example to expedite explanation. It will be appreciated, however, that the principles elucidated herein may be applicable to other arrangements so that the specific examples described herein are not limiting. As sued herein, “almost symmetric” and “substantially symmetric” mean sufficiently symmetric that the OpuS can function for its intended purpose and an image integration module as described below can “see” all of the mirrors simultaneously. According to aspects of an embodiment, in such an arrangement an image integration module is arranged to collect object rays from both the left side optics and right side optics, which is this example are concave mirrors. Thus, in this arrangement, there are several right-left mirror pairs. A camera system including a camera and a lens system is positioned outside the sealed OPuS enclosure. The camera is arranged to collect rays through a sealing window which is transparent to light in the visible portion of the spectrum, that is, in the range of wavelengths from about 380 to about 700 nm. The rays produce an image with half of the image originating from left side concave mirror of a mirror pair and the other half of the image originating from the right side concave mirror of the mirror pair.

Against this backdrop, the conventional method of aligning the optical elements in an OPuS is described in connection withFIG.7. As seen inFIG.7, an OPuS700includes an enclosure710. Within the enclosure710are positioned for optical elements720,730,740, and750. These optical elements may be, for example, mirrors. These optical elements must be aligned so that an incoming beam strikes the optical elements at the proper position. To perform this alignment procedure, the enclosure710is opened and an alignment card760is placed adjacent to the position of the optical surface of one of the optical elements, in the figure, optical element750. The optical element is then aligned so that the beam falls on the proper position on the alignment card760. As set forth above, this method entails several disadvantages such as the need to open the enclosure710and break purge and the need for an operator to insert their hands into the enclosure710in an open beam situation, which can expose the operator's hands to ultraviolet radiation. It also increases the risk of optical contamination and the resultant decrease in the useful lifetime of the optics.

According to an aspect of an embodiment, as shown inFIG.8A, an OPuS800enabling an improved method of alignment includes enclosure810. Located within the enclosure810are optical features820,830,840, and850. Located in a central portion of the enclosure810is an image integration module860. As will be described in further detail below, this image integration module860collects light from the optical features and presents the light to a camera890through a sealing window870and a lens880. In effect, the camera890“sees” all of the optical features within the enclosure810at the same time without any need to open the enclosure810. This permits continuous observation of the alignment state of the OPuS800while avoiding the disadvantages of the prior methods. In some embodiments, the image integration module860is placed as closely to the camera system as possible to maximize the available field of view. Elements835and855are adjustors as will be explained in more detail below.FIG.8Bshows the placement of the image integration module860in relation to the arrangement shown inFIG.5B. Again, the numbers 1-12 indicate the positions of the twelve reflections from the four mirrors.

FIG.9Ashows a possible implementation of the image integration module860according to an aspect of an embodiment. As shown, the image integration module860may be implemented as a pair of mirrored prisms910,920. The prism910is arranged receive light from a region of interest825including at least one optical feature820and redirect the light as shown out through the sealing window870. Similarly, the prism920is arranged to receive light from a region of interest835and redirect the light as shown through the sealing window870. Thus, a camera system including a camera and one or more lenses placed on the other side of the sealing window870simultaneously receives image-forming light from both the left side region of interest825and right side region of interest835. In other words, the image integration module860collects object rays from both left side optical feature and the right side optical feature. A camera and lens system positioned outside the sealed OPuS enclosure820camera collects the object rays through the visible transparent sealing window and produces an image, half of the image being from left side optical feature and the other half being from right side optical feature.

FIG.9Bis a diagram showing the manner in which the image integration module860receives light from both the left side region of interest825containing at least one optical feature and right side region of interest835containing at least one optical feature and redirects the light to a position A from which a virtual object825awhich is an image of the left side region of interest825and from which a virtual object835awhich is an image of the right side region of interest835appear to be collocated, that is, positioned side-by-side, so that they can be viewed simultaneously by a single camera system placed at position A.

According to an aspect of an embodiment, the image integration module860may also be implemented using a pair of mirrored surfaces. As an example, a mirror950, is shown inFIG.10, the other mirror being placed substantially symmetrically across axis970. The conditions for a maximal field of view in such an arrangement are established geometrically also as shown inFIG.10. In the figure, h is the height of the field of interest960, d is the vertical distance between the center of the field to the center of the mirror950, and s is the horizontal distance between the field and the mirror950. The upper part of the figure is the position of a virtual image viewed from below (in the figure) mirror. The angle θs for a maximal field of view between a line980parallel to the field of interest960and passing through a center of the mirror950is then given by the relationships:

θ⁢1=a⁢tan⁡(ds)θ⁢2=a⁢tan[h2-w2⁢2s]θ⁢3=90-θ⁢1-θ⁢22
so that the angle θs, which is the angle of inclination of the mirror950with respect to the optical vertical is given by

θ⁢s=θ⁢2+θ⁢3=90-θ⁢1-θ⁢22=45+[a⁢tan[h2-w2⁢2s]-a⁢tan(ds)]/2

As mentioned, the image integration module860may be implemented in any one of a number of ways. According to aspects of some embodiments, the image integration module860may be implemented as a pair of prisms910,920as shown inFIG.9A, or as a single prism1000with two mirrored surfaces1010and1020as shown inFIG.11A, or as two flat beveled mirrors1030and1040as shown inFIG.11B. However, the image integration module860is implemented, in some embodiments the gap between the optical elements or mirrored surfaces is minimized so as not to waste the portion of the field of view lost to gaps as depicted inFIG.11C. InFIG.11Cthe arrow A depicts the field of view from one of the optical features, e.g., mirror and the arrow B depicts the field of view from the other, paired optical feature, and the arrow C depicts the field of view lost due to the gap between the prisms910,920.

FIG.9Adepicts an arrangement in which the light passing through the sealing window870travels directly in a straight line to the lens system880. For some embodiments it may be advantageous to interpose additional optical elements in the path from the sealing window870to the lens system880. For example,FIG.12Ashows an arrangement in which a folding mirror1100is placed in this path to fold the optical path and create the possibility of providing more compact arrangements. In the arrangement inFIG.12Athe mirror1100is positioned within the enclosure to obtain a larger field of view. This arrangement also provides the ability to adjust the image orientation and improve matching of the size and shape of the field and the image sensor in the camera.FIG.12Bshows an arrangement in which the prisms910a,920aare partially rotated to fold the optical path.FIG.12Bshows the manner in which the image integration module860areceives light from both the left side region of interest825and right side region of interest835and redirects the light to a position B from which a virtual object825bwhich is an image of the left side region of interest825and from which a virtual object835bwhich is an image of the right side region of interest835appear to be collocated, that is, positioned side-by-side, so that they can be viewed simultaneously by a single camera system placed at position B. As shown, this arrangement also provides the ability to adjust the image orientation and improve matching of the size and shape of the field and the image sensor in the camera.

For some embodiments it may also be advantageous to enhance the visibility of the region of interest by providing an alignment feature and by using visible (to the camera) light from fluorescence produced by absorption of ultraviolet light. Using the example of a dichroic mirror as the optical element to be aligned, the mirror in general is supported by a mirror supporting plate1300which includes a support1310and at least one alignment feature1320. According to some embodiments, as shown inFIG.13, a dichroic mirror assembly1330includes a substrate1340which transmits visible light as shown inFIG.13Band a UV reflective coating1360(FIG.13D). The dichroic mirror assembly1330is overlaid on top of the mirror supporting plate1300to produce the sandwich-like structure shown inFIGS.13C and13D. UV radiation striking the dichroic mirror assembly1330will create a visible beam fluorescence footprint1350in a manner described more fully below. The fluorescence generated by the ultraviolet radiation and the back alignment feature can be observed by the camera operating in, for example, the visible spectrum range. By comparing the location of the fluorescence and the alignment feature through the mirror or substrate the system can easily be aligned as described below. While visible light is used in this example, it will be understood that radiation outside of the visible portion of the spectrum may be used.

According to aspects of various embodiments, the illuminated beam footprint may be generated on exposure to UV in any one of a number of different ways. For example, as shown inFIG.14A, the UV reflective coating1360may be selected to be one that exhibits intrinsic fluorescence properties upon exposure to UV. This is indicated inFIGS.14A-14Dwith the thick arrow indicating incident UV radiation and the wavy arrows indicating light produced by fluorescence. Alternatively, as shown inFIG.14B, a back surface of the substrate1340may be provided with a fluorescent coating1370with light being generated by leakage of UV through the reflective coating1360. The term “back surface” when referring to the substrate1340means the substrate surface that faces away from the incoming UV radiation. Alternatively, as shown in FIG.14C, a front surface of the support1310may be provided with a fluorescent coating1380with light being generated by leakage of UV through the reflective coating1360. The term “front surface” when referring to the support1310means the support surface that faces in the direction of incoming UV radiation. Alternatively, as shown inFIG.14D, the support1310may be made of a fluorescent material with light being generated by leakage of UV through the reflective coating1360.

FIG.15Ais a plan view of dichroic mirror assembly1330overlaid on top of the mirror supporting plate1300with alignment feature1320. The mirror supporting plate1300with alignment feature1320are shown in phantom as they are behind the dichroic mirror assembly1330. UV radiation striking the dichroic mirror assembly1330creates a visible beam fluorescence footprint1350as described. In other words, the UV radiation beam will strike the dichroic mirror assembly1330at one or more specific locations as shown, for example, inFIG.5B. The specific area struck by the beam will fluoresce as indicated by the fluorescence footprint1350. The rest of the surface of the dichroic mirror assembly1330not struck by the beam will not fluoresce.FIG.15Ashows an unaligned position in which the fluorescence footprint1350does not sufficiently coincide with the alignment feature1320.FIG.15Bshows an aligned position in which the fluorescence footprint1350does sufficiently coincide with the alignment feature1320. This is accomplished by alignment so that the UV beam lands on the dichroic mirror assembly1330in correct locations (two in the example) which due to fluorescence light up and reveal the relative positioning of the UV footprint and the alignment feature. To correct alignment, the orientation of one or more mirrors is adjusted so that the beam lands in the correct positions on all of the mirrors. The image of the beam landing juxtaposed with the alignment feature is captured by the camera, that is, converted to a digital image which an operator can view while performing an alignment operation.

According to some embodiments, the alignment of the pulse stretcher requires that at least some of the mirrors be adjustable, e.g., in the case of a four mirror arrangement, at least two of the four imaging relay mirrors be adjustable. Each of the two adjustable mirrors has tip/tilt adjustment creating a total of four degrees of freedom. The two adjustable mirrors may be located at opposite ends of the OPuS because of the confocal design of the system. The adjustable mirrors can also be designed with Z-axis (e.g., the direction of the propagation of beam) adjustment, according to some embodiments.

Typically, adjustments on these components to carry out alignment are made using a through-the-wall adjustor (“TWA”) such as adjustors855and835(FIG.8A). These involve the use of a hand-manipulated hex driver to tip or tilt or translate an optic or module. TWAs may provide a sealed mechanical feed through to certain adjustments, e.g., accessed through the covers via a sealed mechanical feed-through. Adjustment can also be carried out with an electrically actuated TWA instead of a manually actuated TWA. A motor is mechanically coupled to the TWA. For example, the motor may have a shaft to which a hex adaptor is attached so that when the motor turns the shaft, the hex driver also turns, causing the end of the TWA to translate along its axis according to the direction of rotation of the shaft. Use of an electrically actuated TWA enables automation of the alignment process with the digital images from the camera890being conveyed to the control system135(FIG.1) which in turn analyzes the images and actuates the TWAs to carry out alignment.

It should be understood that alignment may entail adjusting only one optical feature and that causing the beam to impinge on the proper part of a first optical feature may require adjusting a second optical feature optical feature

FIG.16is a flow chart showing a process for aligning optical features positioned within a sealed enclosure in accordance with aspects of embodiments. In a step S10the optical features within the enclosure are exposed to a beam of UV radiation. The beam of UV radiation makes the footprint of the UV radiation beam visible. In a step S20the light generated by the UV radiation beam fluorescence is combined into a single image from the optical features. The single image is conveyed outside of the enclosed chamber to a camera in a step S30. In a step S40the features are aligned based on the image made from the light combined from the features, either by a technician while viewing the image captured by the camera or by a control system as described above. In essence, in instances where each of the features includes an alignment feature, the alignment is determined based on the positional relationship within the image of the beam footprint and the alignment feature for each optical feature.

The present invention has been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed.

The foregoing description of the specific embodiments will so fully reveal the general nature of the present invention that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance.

Other aspects of the invention are set out in the following numbered clauses:1. An optical component comprising:a sealed enclosure, the sealed enclosure including a window transparent to visible light;a first optical feature positioned at a first position within the enclosure;a second optical feature positioned at a second position within the enclosure; andan image integration module arranged to receive first optical feature light from the first optical feature and second optical feature light from the second optical feature and adapted to redirect the first optical feature light and the second optical feature light through the window to form an image from the first optical feature light collocated with an image from the second optical feature light.2. The optical component as in clause 1 wherein the optical component is an optical pulse stretcher.3. The optical component as in clause 1 wherein the first optical feature comprises a first mirror and wherein the second optical feature comprises a second mirror.4. The optical component as in clause 3 wherein the first mirror comprises a first concave dichroic mirror and wherein the second mirror comprises a second concave dichroic mirror.5. The optical component as in clause 1 wherein the first optical feature and the second optical feature are positioned substantially symmetrically with respect to the image integration module.6. The optical component as in clause 1 wherein the image integration module comprises a first reflective surface arranged to redirect light from the first optical feature and a second reflective surface arranged to redirect light from the second optical surface.7. The optical component as in clause 6 wherein the first reflective surface comprises a first prism reflective surface of a first prism and wherein the second reflective surface comprises a second prism reflective surface of a second prism.8. The optical component as in clause 1 wherein the image integration module comprises a prism having a first reflective surface oriented toward the first optical feature and a second reflective surface oriented toward the second optical feature.9. The optical component as in clause 1 wherein the image integration module comprises two flat beveled mirrors.10. The optical component as in clause 1 further comprising:a third optical feature positioned at a third position within the enclosure; anda fourth optical feature positioned at a fourth position within the enclosure;wherein the image integration module is arranged to receive third optical feature light from the third optical feature and fourth optical feature light from the fourth optical feature and adapted to combine and redirect the third optical feature light and the fourth optical feature light through the window to form an image from the third optical feature light collocated with an image from the fourth optical feature light.11. The optical component as in clause 1 further comprising a camera system arranged to receive the first optical feature light and the second optical feature light through the window.12. The optical component as in clause 11 wherein the camera system comprisesa lens system arranged to receive the first optical feature light and the second optical feature light through the window anda camera arranged to receive the first optical feature light and the second optical feature light from the lens system.13. The optical component as in clause 11 further comprising a folding mirror optically positioned between the image integration module and the window for turning an optical path of the first optical feature light and the second optical feature light.14. The optical component as in clause 1 wherein at least one of the first optical feature and the second optical feature is adjustable, and further comprising an actuator mechanically coupled to the at least one of the first optical feature and the second optical feature to adjust an orientation of the at least one of the first optical feature and the second optical feature.15. The optical component as in clause 1 wherein the first optical feature comprises a first fluorescent material and a first alignment feature and wherein the second optical feature comprises a second fluorescent material and a second alignment feature.16. The optical component as in clause 1 whereinthe first optical feature comprises a first mirror comprising a first substrate transparent to visible light and first reflective coating that is reflective to UV radiation and a first mirror support, and wherein the second optical feature comprises a second mirror comprising a second substrate transparent to visible light and second reflective coating that is reflective to UV radiation and a second mirror support.17. The optical component as in clause 16 wherein the first mirror support comprises a first alignment feature on a front surface of the first mirror support and wherein the second mirror support comprises a second alignment feature on a front surface of the second mirror support.18. The optical component as in clause 17 wherein the first alignment feature corresponds to a position of an aligned beam footprint on the first mirror and wherein the second alignment feature corresponds to a position of an aligned beam footprint on the second mirror.19. The optical component as in clause 18 wherein the first optical feature further comprises a first fluorescent material and wherein the second optical feature further comprises a second fluorescent material.20. The optical component as in clause 19 wherein the first optical feature comprises a first reflective coating including the first fluorescent material and wherein the second optical feature comprises a second reflective coating including the second fluorescent material.21. The optical component as in clause 19 wherein the first fluorescent material is provided on a back surface of the first substrate and wherein the second fluorescent material is provided on a back surface of the second substrate.22. The optical component as in clause 19 wherein the first fluorescent material is provided on a front surface of the first mirror support and wherein the second fluorescent material is provided on a front surface of the second mirror support.23. The optical component as in clause 19 wherein the first mirror support comprises the first fluorescent material and wherein the second mirror support comprises the second fluorescent material.24. An optical component comprising:a sealed enclosure, the sealed enclosure including a window transparent to visible light;a first optical feature positioned within a first field of view within the enclosure;a second optical feature positioned within the first field of view within the enclosure; andan image integration module arranged to receive first field of view light from the first field of view and adapted to combine and redirect the first field of view light through the window, whereinthe image integration module comprises a planar mirrored surface inclined with respect to a line passing through a center of the planar mirrored surface and substantially parallel to the first field of view by an angle θ given by the relationship

θ=45+[a⁢tan[h2-w2⁢2s]-a⁢tan⁡(ds)]/2.where h is a height of the first field of view, d is a vertical distance between the center of the first field of view to the center of the planar mirrored surface, and s is a horizontal distance between the first field of view and the center of the planar mirrored surface.25. A method of aligning a plurality of optical features arranged in sealed enclosure having a window, the method comprising:combining light from each of the optical features to produce a combined light signal;directing the combined light signal out of the enclosure through the window; andaligning at least some of the plurality of optical features based at least in part on the combined light signal.26. The method as in clause 25 further comprising imaging the combined light signal after directing the combined light signal out of the enclosure through the window using a camera system positioned outside of the sealed enclosure and arranged to receive the combined light signal.27. The method as in clause 25 wherein each of the plurality of optical features comprises an alignment feature and a fluorescent material arranged to generate a visible footprint of a UV beam impinging on the optical feature and further comprising, before combining light from each of the optical features to produce a combined light signal,exposing each of the optical features to a beam of UV radiation, andgenerating an illuminated footprint of the beam of UV radiation on each of the optical features,wherein aligning at least some of the plurality of optical features based at least in part on the combined light signal comprises aligning at least some of the plurality of optical features based at least in part on a positional relationship of the illuminated footprint and the alignment feature for each optical feature.28. The method as in clause 25 wherein aligning comprises adjusting one or more of the plurality of optical features.29. The method as in clause 28 wherein adjusting one or more of the plurality of optical features comprises manually operating one or more actuators respectively mechanically coupled to the one or more of the plurality of optical features.30. The method as in clause 28 wherein adjusting one or more of the plurality of optical features comprises supplying a signal to actuate one or more motor driven actuators respectively mechanically coupled to the one or more of the plurality of optical features.31. The method as in clause 28 wherein adjusting one or more of the plurality of optical features comprises adjusting an orientation of one or more of the plurality of optical features.