Monolithic Offner Spectrometer

Description of related application

This application claims the benefits of US Provisional Patent Application No. 60/795916 filed on April 28, 2006 and US Provisional Patent Application No. 60/795917 filed on April 28, 2006. The contents of the specification of the above application are included herein as a reference.

The present invention relates to the field of high resolution spectral imaging, in particular to monolithic Offner spectrometers and various components such as gratings and slits, all made using the latest diamond machining processes.

A spectroscope is a device that receives an optical signal as an input and generates an optical signal as an output, which is spatially dispersed or dispersed according to various wavelength components of the input optical signal, that is, color. A detector attached to the spectroscope can analyze the output signal, called a spectrum, to quantify the magnitude of each wavelength component present in the input signal.

A unique type of spectroscope known as the Offner spectroscope can be used to form images of remote objects over a narrow continuous spectrum band. This type of imaging is known as high resolution spectral imaging and has recently emerged as an important element of military / aerospace solutions for aerial and space reconnaissance and remote exploration. Basically, a high resolution spectral imaging system uses an Offner spectrometer and advanced data processing technology to generate an image with embedded spectral identification characteristic data. This discriminating property data is useful in a wide range of applications such as (eg) targeting / recognition, missile flame identification and deposit detection.

In addition, high resolution spectral imaging systems can also be used in a wide range of consumer applications such as (eg) cancer detection, environmental monitoring, agricultural monitoring and mineral exploration. Due to the importance of high resolution spectral imaging systems in military, aerospace and commerce, manufacturers are new and better at creating and improving the performance of Offner spectrometers and ancillary components such as slits and gratings. We are actively working on the development of such means.

<p>Some new fabrication processes as well as Offner spectrometers created as a result of such processes and ancillary components such as slits and gratings are the subject of the present invention.</p>

<p> As used herein, various components such as monolithic Offner spectrometers and diffraction gratings and slits, all of which are made using the latest diamond machining processes, are described. In one embodiment, the monolithic Offner spectrometer is made directly using a diamond machining process. In another embodiment, the monolithic Offner spectrometer is made using a mold made in a diamond machining process. In yet another embodiment, the diffraction grating is created directly using a diamond machining process. In yet another embodiment, the diffraction grating is made using a mold made in a diamond machining process. In yet another embodiment, the slits are created directly using a diamond machining process.</p>

The present invention can be further fully understood by reference to the following detailed description provided with the accompanying drawings.

Referring to FIG. 1, a block diagram shows a high resolution spectral imaging system 100 incorporating a monolithic Offner spectroscope 102 configured and created in accordance with the present invention. The high resolution spectral imaging system 100 has a slit 104 and a detector 106, both of which protect the monolithic Offner spectroscope 102 (which could be made of the same material as the slit 104). It is attached to the body 107. As shown, the monolithic Offner spectroscope 102 has a light incoming surface 108, (formed when the exposed region 109 / first surface 109 of the translucent material 101 is coated with a reflective coating 118). 1 mirror 110, diffraction grating 112 (formed when the reflective coating 118 is applied to the exposed region 113 / second surface 113 of the translucent material 101), (exposed region 115 / th of the translucent material 101). A one-to-one optical relay made of a single translucent material 101 having a second mirror 114 and a light emitting surface 116 (formed when a reflective coating 118 is applied to the surface 115 of 3). The monolithic Offner spectrometer 102 could be constructed using one of the two methods 200 and 300 discussed below with respect to FIGS. 2 and 3.

In the high resolution spectrum imaging system 100, the slit 104 receives the beam 120 from a remote object (not shown), diffracts the beam 120, and sends the diffracted beam 120'to the detector 106. When deriving, it works to form an image of a remote object over a narrow continuous spectral band. Specifically, the slit 104 guides the beam 120 to the diamond machined flat input surface 108. The first mirror 110 (spherical mirror 110) then receives the beam 120 that has entered the light entry surface 108 and directs the beam 120 toward the diffraction grating 112 (which has the same shape as the diffraction grating shown in FIGS. 5-8). reflect. The diffraction grating 112 receives the beam 120, diffracts it, and reflects the diffraction beam 120'on the second mirror 114 (spherical mirror 114). The second mirror 114 receives the diffracted beam 120'and reflects the diffracted beam 120'on the diamond machined light emitting surface 116. The detector 106 (eg, the two-dimensional focal plane array 106 (FPA106)) receives and processes the diffracted beam 120'that has passed through the light emitting plane 116. The particular type of detector 106 used will have wavelength (color) sensitivity based on the type of translucent material 101 used to make the monolithic Offner spectrometer 102. For example, if the monolithic Offner spectrometer 102 is made of plastic (eg, polymethylmethacrylate (PMMA), polystyrene, polycarbonate), the wavelength will be in the visible region and the detector 106 will be a complementary metal-oxide-semiconductor. It could be a (CMOS) video camera 106. If the monolithic Offner spectrometer 102 is made of an infrared transmissive material, the detector 106 must be an IR detector that can be based on mercury cadmium telluride (HgCdTe) or indium antimonide (InSb). Will not be.

The monolithic Offner spectrometer 102 described above has several desirable features and advantages, some of which are discussed next.

The monolithic Offner spectroscope 102 is lighter than a conventional outdoor Offner spectroscope (consisting of individual components).

The monolithic Offner spectrometer 102 is easy to thermalize, which is a desirable property for aerospace / aerial applications.

The Monolithic Offner Spectrometer 102 has a relatively small ground contact area, which not only makes it more cost effective, but also (eg) medical, analytical, head-up display (HUD), night vision and helmet-mounted display (HMD) applications. It is attractive to.

The monolithic Offner spectrometer 102 could form conical and aspheric outer surfaces, if desired.

The diffraction grating 112 has a larger wavelength dispersion / separation than an exposed diffraction grating having the same lattice period (groove spacing).

With reference to FIG. 2, a flowchart shows the steps of a preferred method 200 for making a directly machined monolithic offner spectroscope 102 according to the present invention. In step 202, the translucent material 101 used to form the monolithic Offner spectroscope 102 needs to be selected. The Monolithic Offner Spectrometer 102 is made of any type of diamond machined translucent (refractive optical) material such as (eg) PMMA, polystyrene, polycarbonate, silicon, germanium, zinc selenide, zinc sulfide. Let's be able to. However, there are several factors that can play a role in what type of translucent material 101 should be selected, such factors as the spectral region required for the particular application and the refraction of the translucent material 101. There is a rate.

When the translucent material 101 is selected, the translucent material 101 is attached and secured to a computer numerically controlled (CNC) diamond lathe so that a diamond tool can be used to form the monolithic Offner spectrometer 102. To. In step 204, a diamond tool is used to machine the translucent material 101 into a diamond machine to form the light entry surface 108. In step 206, a diamond tool is used to machine the translucent material 101 into a region that will become the first mirror 110. In step 208, a diamond tool is used to machine the translucent material 101 into a region that will become a grating (with the same shape as the grating shown in FIGS. 5-8). In step 210, a diamond tool is used to machine the translucent material 101 into a region that will become the second mirror 114. In step 212, a diamond tool is used to machine the translucent material 101 into a diamond light emitting surface 116. Once the diamond machining steps 204,206, ..., 212 have been completed, then in step 214, the diamond machined transparent to form the first mirror 110, the grating 112 and the second mirror 114. A reflective coating 118 (back coating 118) is applied to the corresponding exposed area of the light material 101. For example, the reflective coating 118 could be applied using any one of the vacuum techniques commonly used in the optical industry. At this point, the directly machined monolithic Offner spectrometer 102 has been created (see FIG. 1).

With reference to FIG. 3, a flowchart shows the steps of method 300, which is preferable for producing the molded monolithic Offner spectroscope 102 according to the present invention. In step 302, a first mold 402 (which could be made of nickel) is mounted and secured on a CNC diamond lathe. The first mold 402 is then diamond machined to form mirror images 404 and 406 in the first mold 402 that are associated with the regions to be the first mirror 110 and the second mirror 114, respectively. A diamond tool is used (step 304). FIG. 4 is a schematic diagram showing an exemplary first mold 402 in which mirror images 404 and 406 are formed associated with the regions to be the first mirror 110 and the second mirror 114, respectively.

In step 306, a second mold 408 (which could be made of nickel) is mounted and secured on a CNC diamond lathe. The second mold 408 is then diamond machined and associated with the region to be the light incoming surface 108, the diffraction grating 112 (same shape as the diffraction grating shown in FIGS. 5-8) and the light emitting surface 114, respectively. A diamond tool is used to form the mirror images 410, 412 and 414 into the second mold 408 (step 308). FIG. 4 is a schematic diagram showing an exemplary second mold 408 in which mirror images 410, 412 and 414 are formed, which are associated with regions that should be the incoming surface 108, the diffraction grating 112 and the outgoing surface 114, respectively. is there.

In step 310, the first mold 402 and the second mold 416 are connected / attached to both ends of the mold cavity 416, respectively (FIG. 4). In step 312, the translucent material 101 is injected / injected into the cavities formed in the first mold 402, the second mold 408, and the mold cavity 416. For example, step 312 could be part of an injection molding process, compression molding process or injection molding process. The translucent material 101 can be any type of refracting optical material (eg) such as PMMA, polystyrene, polycarbonate. However, there are several factors that can play a role in which type of translucent material 101 should be used, such factors as the spectral region required for the particular application and the index of refraction of the translucent material 101. is there.

In step 314, the first mold 402, the second mold 408, and the mold cavity 416 are separated from each other in order to expose the molded translucent material 101. In step 316, a reflective coating 118 (back coating 118) is applied to the exposed back region of the molded translucent material 101 in order to form the first mirror 110, the diffraction grating 112 and the second mirror 114. Again, the reflective coating 118 could be applied using any one of the vacuum techniques commonly used in the optical industry. At this point, the molded monolithic Offner spectrometer 102 has been created (see FIG. 1).

Referring to FIG. 5, there is a block diagram of a free-standing diffraction grating 502 formed according to the present invention (the free-standing diffraction grating 502 has the same characteristics as the diffraction grating 112 discussed above in FIG. 1, but is not the same. Absent). As shown, the diffraction grating 502 has a large number of gratings 504 formed within the beam deflection plane 506 (eg, spherical surface 506, torus plane 506). Each line grid 504 has a blaze surface 508 (or a double facet blaze surface 508a or a beam deflection blaze surface 508b) tilted according to a blaze angle 510 that varies within the beam deflection surface 506. Further, each line grid 504 has a period 512 defined at intervals of two ruled lines 514a and 514b. Each of the ruled lines 514a and 514b has a region referred to herein as a blaze reset 516. A discussion of how the diffraction grating 502 can be made is given next with respect to FIG.

With reference to FIG. 6, a flowchart shows the steps of method 600, which is preferable for producing the diffraction grating 502 according to the present invention. In step 602, the grating blank 502'(which later becomes the grating 502) is mounted and fixed on the CNC diamond lathe. In one embodiment, the grating blank 502'is mounted at an angle of 90 ° with respect to the spindle axis of the CNC diamond lathe. Therefore, in one plane, the grating blank 502'shows a circular cross section. On the other plane, the grating blank 502'shows a side surface that is diamond machined according to the CNC program to form a pre-determined grating 502.

In step 602, the CNC program of the diamond tool 520 (preferably having a radius smaller than the blaze reset 516) spans the path defined by the grid profile to form the grid 504 on the beam deflection plane 506 (curved surface 506). Control movement and movement. Changes in the blaze angle 510 along the beam deflection surface 506 are also controlled by the CNC program. This process can be used to form a lattice period 512 in the range of a few μm to a few mm. 7A and 7B show photographs and two profile measurement results for an exemplary diffraction grating 502 made according to the present invention, respectively.

In a preferred embodiment, the diamond tool 520 has a tip with a radius in the range of 0.5 μm to 20 μm. Since the tip radius of the diamond tool is very small, the feed rate of the CNC diamond lathe needs to be very slow to obtain the desired optical finish. In addition, the CNC diamond lathe needs to operate with a feedback resolution of less than 10 nm. This type of manufacturing process takes a long time, and as a result, the uniformity of the lattice period 512 can be sensitive to the thermal stability of the CNC diamond lathe. To address this issue, the blaze surface 508 / blaze angle 510 can be machined first, and then the blaze reset 516 (which defines the period 512) can be machined using another more time-efficient CNC program. You can do it. When this is completed, the grating 512 will have a surface finish with the characteristic "fingerprint". FIG. 8 is a graph showing a repeating structure of the exemplary property "fingerprint" as seen in an optical profiler for one of the blaze planes 508. This particular property "fingerprint" had a roughness (Ra) of ~ 1 nm. The repeating structure of this property "fingerprint" is a means that could be used to determine if a diffraction grating is made according to the present invention.

The fabrication method 600 described above and the grating 512 created have some desirable features and advantages, some of which are discussed next.

The making method 600 can be used to form a convex or concave surface, which means that a mold for duplicating a plurality of diffraction gratings 502 can be made (see, for example, FIG. 4). This is desirable because it allows the molded diffraction grating 502 to be mass-produced with the high cost efficiency required for consumer applications.

The fabrication method 600 could be used to fabricate the grating 112 as is part of the monolithic Offner spectrometer 102 discussed above with respect to FIGS. 1-4. In this case, the diffraction grating 112 has the following features: (1) line grating 504, (2) beam deflection surface 506, (3) blaze surface (double facet blaze surface 508a, beam deflection blaze surface 508b), (4) blaze. It will have angles 510 (variable blaze angle 510) and (5) blaze reset 516.

The diffraction grating 502 has a profile of a metal (eg, nickel, copper, aluminum) or a glass-like material (eg, germanium, silicon, CaF)._２), So it is mechanically and environmentally stable.

The grating 502 can also have a mounting / alignment structure (eg, screw holes) that is machined during the machining process.

The CNC program and the small diamond tool 520 together ensure that the change in blaze angle 510 is machined to match a particular light incident angle at a particular position on the beam deflection plane 506. This change in blaze angle 510 improves efficiency. Moreover, this change in blaze angle 510 is an additional degree of freedom in design that would not have been previously available.

The blaze surface 508 need not be a flat surface having a blaze angle 510 optimized for one wavelength. Alternatively, the blaze surface 508 can be a faceted surface or a "beam deflection surface" to optimize performance over the extended operating wavelength range. FIG. 5 shows an exemplary double facet blaze surface 508a and an exemplary beam deflection blaze surface 508b.

The designer can control the manufacturing process to vary the period 512 to correct for optical aberrations. Alternatively, the designer can vary the period 512 so that multiple openings with different periods can be used on a common substrate.

The blaze reset 516 between the two blaze surfaces 508 can have an angle that changes as well as a change in the blaze angle 510. However, this is not a requirement of the present invention. The small diamond tool 520 makes it possible to obtain the ability to change the blaze reset angle at a different angle than the blaze angle 510 associated with the blaze surface 508, using the same points on the tool 520.

-This preparation process has been demonstrated to be applicable to nickel plating, copper plating, crystal materials (eg germanium, silicon, etc.) and aluminum alloys (eg Corning NetOptix LLC aluminum alloys). Aluminum alloys are of particular importance because many military applications happen to have an aluminum mounting structure and also have a wide operating temperature. That is, the ability of the grating 502 to be made of an aluminum alloy is beneficial because it will not be as significantly deformed as it would be if the grating was made of a (coated) two-layer metal substrate.

With reference to FIGS. 9A-9D, each figure shows a slit 900 formed according to the present invention. In practice, the slit 900 will be located in front of the incoming surface of the spectroscope. For example, the slit 900 could be placed in front of the incoming surface 108 of the monolithic Offner spectrometer 102 shown in FIG. The main function of most spectroscopes (including the Monolithic Offner spectrometer 102) is to divide the line image into 2D spectral images, one dimension being space and the other dimension being spectrum. Should be noted. The main function of the slit 900 is to act as a field diaphragm and accept only a single line image (generally slightly wider than the individual detector elements).

The illustrated slit 900 is diamond machined, having a first surface having a region 906 removed in a diamond ball cutting edge milling process to determine the length of the slit opening 908 (see step 1002 in FIG. 10). It can be made of a possible substrate 902 (eg copper, nickel, aluminum, silicon, germanium, gold, calcium fluoride). The diamond machinable substrate 902 is removed in a diamond flycut process to form a groove 914 that penetrates the first surface 904 to form a slit opening 908 (see step 1004 in FIG. 10) region 912. Also has a second surface 910. Finally, a precision mounting structure 916 can also be formed on the diamond machined substrate 902 (see step 1006 in FIG. 10). A detailed discussion of how slits could be formed is given next with respect to FIGS. 11 and 12.

With reference to FIGS. 11A-11B, two photographs of the exemplary slit 900 made according to the present invention are shown. This particular slit 900 was made by providing a stress-relieved aluminum blank 902, which was plated with ~ 0.015 inch (about 0.38 mm) thick electroless nickel plating (element 902). Is shown in FIGS. 9A-9D). Nickel was used because it has a much lower ductility than aluminum and the combined use of nickel gives a slit 908 of significantly better quality than would be obtained if only aluminum were used. The faces of this part 902 were then diamond fly cut on a diamond lathe to remove ~ 0.005 inches (about 0.13 mm) from each face so as to maintain precise parallelism. A diamond tool 1202 with a single corrugated cutting edge (see Figure 12A) was attached to a 3-axis diamond machining system (similar to a 3-axis milling machine, but with higher precision, air bearings, etc.). Using a diamond tool 1202, nickel and aluminum were pierced and bitten into the nickel layer on the second surface 910 of the part 902 by ~ 0.005 inch to machine the columnar groove 906 and the length of the slit 908. (See step 1002 in FIG. 10) (elements 906, 908 and 910 are shown in FIGS. 9A-9D). At this point, ~ 0. A 005 inch thick nickel "skin" is left in the slit area. Part 902 was then attached to another diamond lathe known as a 3-axis fly cutter. A diamond tool 1204 (see FIG. 12B) was attached to the outer diameter of the fly cutter head with the sharp "tip" of the tool 1204 facing outward in the radial direction from the axis of rotation of the fly cutter. The shape and dimensions of the diamond tool 1204 were also determined by the optical F-number that the slit 900 must have and also by the width of the slit opening 908. The part 902 was then attached and a V-groove 914 was cut out on the second surface 910 to form the final slit 908 (elements 902, 908, 910 and 914 are shown in FIGS. 9A-9D). FIG. 11B is an image of a 30 μm wide slit 908 at a magnification of 400, showing the quality that can be obtained by the present production method 1000.

The fabrication method 1000 and the slit 900 created described above have some desirable features and advantages, some of which are discussed next.

The slit 900 can be made of the same material as the optical enclosure (which houses the Offner spectroscope or other spectroscope). This is desirable because it will enhance the thermal performance and structural robustness of the imaging system. For example, two known fabrication methods for slits utilize substrates made of chrome / glass and copper electroformed. None of these materials have good thermal alignment with the aluminum housing.

-Diamond tools 1202 and 1204 can have any one of various shape dimensions such as sphere, plane, pointed, etc.

The production method 1000 enables the formation of the precision mounting structure 916 used for determining the position and orientation of the slit 900 in the final assembly device into the slit 900. Most imaging systems require precise alignment between the slit 900 and the gratings 112 and 502 (see FIGS. 1 and 5), and therefore the formation of such a precision mounting structure 916 when creating the slit 900 is considerable. Benefits can be realized.

With reference to FIGS. 13A-13B, the two schematics show a slit 900'with a curved slit opening 908' and a slit 900'with a plurality of slit openings 908', respectively, according to the present invention. To create the slit 900', step 1004 of method 1000 would be performed by off-axis and mounting the substrate 902 on a diamond lathe. If this were done, a curved slit opening 908'would be created. The curved slit 900'can be beneficial to the Offner and Dyson spectrometers, as best optical performance is obtained over a curve that is symmetric to the axis of the spectrometer. This is not commonly used because the detector usually has a linear pixel sequence. However, the use of curved slits 900'may be desirable for certain applications. Also, in order to create the slit 900 ", the diamond machining steps 1002 and 1004 of Method 1000 could be repeated more than once on the substrate 902. The slit 900" could be used in a 3D high resolution spectrum imaging system. It could be used.

Some embodiments of the present invention are shown in the accompanying drawings and described in detail above, but are not limited to the embodiments disclosed by the present invention, as described and defined in the appended claims. It goes without saying that numerous reconstructions, modifications and substitutions can be made without departing from the spirit of the present invention.

<figref num="1">FIG. 3 is a block diagram showing a high resolution spectral imaging system incorporating a monolithic Offner spectrometer formed according to the present invention.</figref><figref num="2">It is a flowchart which shows the process of the preferable method for making a direct machined monolithic Offner spectroscope according to this invention.</figref><figref num="3">It is a flowchart which shows the process of the preferable method for making the molded monolithic Offner spectroscope according to this invention.</figref><figref num="4">FIG. 3 is a block diagram showing three molds that can be used to create a molded monolithic Offner spectrometer using the method shown in FIG. 3 according to the present invention.</figref><figref num="5">It is a block diagram which shows the diffraction grating formed according to this invention.</figref><figref num="6">It is a flowchart which shows the process of the preferable method for making a direct machined diffraction grating according to this invention.</figref><figref num="7A">The photograph of the example diffraction grating made according to this invention is shown.</figref><figref num="7B">Two profile measurement results for an exemplary diffraction grating created according to the present invention are shown.</figref><figref num="8">It is a graph which shows the roughness characteristic of the iterative structure on the blaze plane of the line lattice in the diffraction grating produced according to this invention.</figref><figref num="9A">It is a figure which shows the slit formed according to this invention.</figref><figref num="9B">It is another figure which shows the slit formed according to this invention.</figref><figref num="9C">It is another figure which shows the slit formed according to this invention.</figref><figref num="9D">It is another figure which shows the slit formed according to this invention.</figref><figref num="10">It is a flowchart which shows the process of the preferable method for making a slit according to this invention.</figref><figref num="11A">It is a photograph of an exemplary slit created using the method shown in FIG. 10 according to the present invention.</figref><figref num="11B">Another photograph of an exemplary slit made using the method shown in FIG. 10 according to the present invention.</figref><figref num="12A">FIG. 5 shows a type of diamond tool used to create the exemplary slits shown in FIGS. 11A-11B according to the present invention.</figref><figref num="12B">FIG. 5 shows another type of diamond tool used to create the exemplary slits shown in FIGS. 11A-11B according to the present invention.</figref><figref num="13A">It is a figure which shows the slit which has the curved slit opening according to this invention.</figref><figref num="13B">It is a figure which shows the slit which has a plurality of slit openings according to this invention.</figref>

Code description

100 high resolution spectral imaging system 101 Translucent material 102 Monolithic Offner Spectrometer 104 slit 106 detector 107 Optical housing 108 Incoming surface 109 Exposed area / First surface 110,114 mirror 112 diffraction grating 113 Exposed area / Second surface 115 exposed area / third surface 116 Idemitsu surface 118 Reflective coating 120 beam 120'diffraction beam