WO2012099987A2

WO2012099987A2 - Multichannel spectrometers

Info

Publication number: WO2012099987A2
Application number: PCT/US2012/021761
Authority: WO
Inventors: Lian-Qin Xiang
Original assignee: Ningbo Yuanlu Electro-Optics, Co., Ltd.
Priority date: 2011-01-20
Filing date: 2012-01-18
Publication date: 2012-07-26
Also published as: WO2012099987A3

Abstract

The invention generally relates to spectrometers and optical systems useful therein. More particularly, the invention generally relates to optical systems and systems having improved functionalities, flexibilities, and design options. For example, optical systems of the invention employ an aberration-corrected concave grating along with an optical assembly comprising one or more transmissive aberration correctors.

Description

MULTICHANNEL SPECTROMETERS

Priority Claims and Related Applications

[0001] This application claims the benefit of U.S. Provisional Application No. 61/434,732 filed January 20, 2011, the entire content of which is expressly incorporated herein by reference.

Technical Field of the Invention

[0002] The invention generally relates to spectrometers and optical systems useful therein. More particularly, the invention generally relates to spectrometers and optical systems having two or more channels and improved functionalities, flexibilities, and related design options.

Background of the Invention

[0003] A spectrometer is an instrument used to measure and/or record properties of radiation such as visible or invisible light over a specific portion of the electromagnetic spectrum. A spectrometer separates incoming radiation into a frequency or wavelength spectrum and is used in spectroscopic analysis to identify and/or analyze materials, for example. Spectrometers produce spectral lines (energy bands) which allow measurement, recordation and analyses of components wavelengths and intensities thereof. Spectrometers typically operate over a pre-selected range of wavelengths, for example, from gamma rays and X-rays into the far infrared.

[0004] A spectrometer often includes a diffraction grating, which is an optical device with a periodic structure. A diffraction grating splits and diffracts light into constituent beams and directs them into different directions. The directions of these component beams depend on factors including the spacing of the grating, the wavelength of the input light and the incident angle. Each constituent wavelength of input beam spectrum is directed to a different direction, so as to produce a rainbow of wavelengths.

[0005] Spectrometers have evolved over time and have been designed for a variety of applications and utilities. While functionalities and qualities have improved from the traditional Czerny-Turner system, significant challenges remain in designing spectrometers that allow the combination of high quality spectroscopy, flexibility in system design and system, and unique functionalities such as compactness and portability. Summary of the Invention

[0006] The invention is based in part on the unexpected discovery of a novel spectrometer optical system that possesses a unique combination of various desired features and advantages, including compact size, portability, and high quality spectroscopy over large continuous wavelength ranges. As will be discussed later, optical systems of the invention employ two, three or more optical channels and an aberration-corrected concave grating along with one or more transmissive aberration correctors.

[0007] Beneficial features of the optical systems and spectrometers of the invention include:

[0008] (1) Compact design with physical dimensions substantially smaller than conventional spectrometers of similar functionalities. The compactness and light weight of the optical systems of the invention allows the production of portable, high resolution and dynamic range spectrometers.

[0009] (2) The system includes an aberration-corrected concave grating, for example with non-equal spaced and curved fringe patterns. This feature allows much more freedom and flexibility in the design and arrangement of the optical components in particular and the optical system in general.

[0010] (3) The optical systems of the invention offers superior dispersion than reflective Off er spectrometers, where dispersion cannot be large as the diffraction beam would be blocked by the convex grating if the dispersion of the grating increases beyond a certain threshold. The optical systems of the invention are not so constrained.

[0011] In one aspect, the invention generally relates to an optical system. The optical system includes: a plurality of optical entrances, each for receiving a radiation from a source object to be imaged; a first transmissive aberration corrector in optical communication with the plurality of entrances; an aberration-corrected concave diffraction grating in optical communication with the first transmissive aberration corrector, wherein the aberration- corrected concave diffraction grating includes a plurality of grooves that are non-parallel and unequally-spaced; a second transmissive aberration corrector in optical communication with aberration-corrected concave diffraction grating; and a plurality of image planes, corresponding to the plurality of optical entrances respectively, each of the image planes is in optical communication with the second transmissive aberration corrector for recording a spectral image of the corresponding entrance. The radiation of the source object is refracted through the first transmissive aberration corrector, projected onto and diffracted from the aberration-corrected concave diffraction grating, refracted through the second transmissive aberration corrector before projected on to one of the plurality of image planes to form the spectral image. The first and the second transmissive aberration corrector can be formed by a single lens or an optical assembly with a group of lenses. The surfaces of these lenses can be any suitable geometries, for example, planar, spherical or aspherical.

[0012] In another aspect, the invention generally relates to a method for recording an optical image. The method includes: directing the radiation from a source object into a plurality of optical entrances; refracting the radiation through a first transmissive aberration corrector; projecting the refracted radiation onto an aberration-corrected concave diffraction grating thereby generating a diffracted radiation from the diffraction grating, wherein the aberration-corrected concave diffraction grating includes a plurality of grooves that are non- parallel and unequally-spaced; refracting the diffracted radiation through the second transmissive aberration corrector; and projecting the refracted radiation from the second transmissive aberration corrector on to a plurality of image planes to form spectral images.

[0013] In yet another aspect, the invention generally relates to a compact portable optical system. The compact portable optical system includes: three optical entrances, each for receiving a radiation from a source object to be imaged; a first transmissive aberration corrector in optical communication with the plurality of entrances; an aberration-corrected concave diffraction grating in optical communication with the first transmissive aberration corrector, wherein the aberration-corrected concave diffraction grating includes a plurality of grooves that are non-parallel and unequally-spaced; a second transmissive aberration corrector in optical communication with aberration-corrected concave diffraction grating; and three image planes, corresponding to the plurality of optical entrances respectively, each of the image planes is in optical communication with the second transmissive aberration corrector for recording a spectral image of the corresponding entrance. The radiation of the source object is refracted through the first transmissive aberration corrector, projected onto and diffracted from the aberration-corrected concave diffraction grating, refracted through the second transmissive aberration corrector before projected on to one of three image planes to form the spectral image, wherein the optical system having a resolution is about 20 pm to about 100 pm.

[0014] In yet another aspect, the invention generally relates to an optical system. The optical system includes: a plurality of optical entrances, each for receiving a radiation from a source object to be imaged; a first optical assembly in optical communication with the plurality of entrances; an aberration-corrected concave diffraction grating in optical communication with the first optical assembly, wherein the aberration-corrected concave diffraction grating includes a plurality of grooves that are non-parallel and unequally-spaced; a second optical assembly in optical communication with aberration-corrected concave diffraction grating; and a plurality of image planes, corresponding to the plurality of optical entrances respectively, each of the image planes is in optical communication with the second optical assembly for recording a spectral image of the corresponding entrance. The radiation of the source object is refracted through the first optical assembly, projected onto and diffracted from the aberration-corrected concave diffraction grating, refracted through the second optical assembly before projected on to one of the plurality of image planes to form the spectral image.

Brief Description of the Drawings

[0015] FIG. 1 schematically illustrates an exemplary embodiment of the optical system of the invention having a three-detector imaging system, showing the configuration in the y-z plane.

[0016] FIG. 2 schematically illustrates an exemplary embodiment of the optical system of the invention having a three-detector imaging system, showing the configuration in the x-z plane.

[0017] FIG. 3 schematically illustrates an exemplary embodiment of the optical system of the invention having a two-detector imaging system, showing the configuration in the y-z plane.

[0018] FIG. 4 schematically illustrates an exemplary embodiment of the optical system of the invention having a two-detector imaging system, showing the configuration in the x-z plane.

[0019] FIG. 5 schematically illustrates exemplary gratings useful in the invention.

[0020] FIG. 6 schematically illustrates an exemplary embodiment of the optical system of the invention having a three-detector imaging system.

[0021] FIG. 7 schematically illustrates an exemplary embodiment of the optical system of the invention having a two-detector imaging system.

[0022] FIG. 8 schematically illustrates an exemplary embodiment of the optical system of the invention having a four-detector imaging system.

[0023] FIG. 9 schematically illustrates an exemplary embodiment of the optical system of the invention having an out-of -plane configuration with a larger NA (0.60) and an aberration corrector with an optical assemble in y-z plane. The out-of-plane configuration is benefitial to reducing stray light on the image plane.

[0024] FIG. 10 schematically illustrates an exemplary embodiment of the optical system of the invention having a tilted in-plane configuration, showing the configuration in the x-z plane.

Detailed Description of the Invention

[0025] The invention is based in part on a uniquely designed compact spectrometer optical system that possesses a novel combination of various desired advantages, including compactness, light-weight, design flexibilities, and high quality spectroscopy. Optical systems of the invention employ an optical assembly that may include one, two, three or more channel aberration-corrected concave grating system along with one or more transmissive aberration correctors. The system also may be designed to have an out-of-plane configuration and/or a titled in-plane configuration to optimize the image quality.

[0026] FIG. 1 schematically illustrates an exemplary embodiment of the optical system of the invention, showing the configuration in the y-z plane. A three channel optical system 100 includes three entrances 110a, 110b, and 110c (each being a slit or an aperture), which receives a radiation from a source object 104, which in general is not part of the optical system.

[0027] A transmissive aberration corrector 120 that is in optical communication with the entrance 110a, 110b, and 110c. The transmissive aberration corrector 120 is also in optical communication with the aberration-corrected concave diffraction grating 140. An image plane 180 (for display, measurement or recording) is in optical communication with the aberration-corrected concave diffraction grating 140. The transmissive aberration corrector 120 includes a receiving surface 124 in optical communication with the entrances 110a, 110b, and 110c and an output surface 128 in optical communication with the aberration- corrected concave diffraction grating 140. The transmissive aberration corrector 120 also includes a receiving surface 164 in optical communication with the aberration-corrected concave diffraction grating 140 and an output surface 168 in optical communication with the image plane 180, whereon spectroscopic images 190a, 190b, and 190c, are recorded, corresponding to entrances 110a, 110b, and 110c, respectively.

[0028] FIG. 2 schematically illustrates an exemplary embodiment 200 of the optical system of the invention having a three-channel system, showing the configuration in the x-z plane. In this embodiment, radiation from the source object 204 is first passed through three entrances 210a, 210b, and 210c, and the three beams then independently pass through the transmissive aberration corrector 220. The transmitted radiation beams arrive at the aberration-corrected concave diffraction grating 240 and are diffracted therefrom. The diffracted radiation beams are passed through the transmissive aberration corrector 220 again, after which the radiation beams are focused on the image plane 280 for display, producing spectroscopic images 290a, 290b, and 290c, measurement or recording.

[0029] FIG. 3 schematically illustrates another exemplary embodiment 300 of the optical system of the invention, showing the configuration in the y-z plane, where a two-channel system produces two sets of spectroscopic images on the imaging plane. The optical system 300 includes two entrances 310a and 310b (each being a slit or an aperture), which receives a radiation from a source object 304, which in general is not part of the optical system.

[0030] A transmissive aberration corrector 320 that is in optical communication with the entrance 310a and 310b. The transmissive aberration corrector 320 is in optical

communication with the aberration-corrected concave diffraction grating 340. An image plane 380 (for display, measurement or recording) is in optical communication with the aberration-corrected concave diffraction grating 340. The transmissive aberration corrector 320 includes a receiving surface 324 in optical communication with the entrance 310 and an output surface 328 in optical communication with the aberration-corrected concave diffraction grating 340. The transmissive aberration corrector 320 also includes a receiving surface 364 in optical communication with the aberration-corrected concave diffraction grating 340 and an output surface 368 in optical communication with the image plane 380, whereon spectroscopic images 390a and 390b, are recorded, corresponding to entrances 310a and 310b, respectively.

[0031] FIG. 4 schematically illustrates an exemplary embodiment 400 of the optical system of the invention, showing the configuration in the x-z plane, where a two-channel system produces two sets of spectroscopic images on the imaging plane. The optical system 400 includes two entrances 410a and 410b (each being a slit or an aperture), which receives a radiation from a source object 404, and the two beams then independently pass through the transmissive aberration corrector 420. The transmitted radiation beams arrive at the aberration-corrected concave diffraction grating 440 and are diffracted therefrom. The diffracted radiation beams are passed through the transmissive aberration corrector 420 again, after which the radiation beams are focused on the image plane 480 for display, producing spectroscopic images 490a and 490b, measurement or recording. [0032] A diffraction grating is a spectral optical component which separates an incident polychromatic beam into its constituent wavelength components, i.e., it is dispersive and directs component beams into different directions. The directions of these beams depend on the fringe spacing of the grating, the wavelength of the light, the incident angle of light and diffraction order.

[0033] FIG. 5 schematically illustrates an embodiment of the aberration-corrected concave diffraction gratings (e.g., 140, 240) according to the invention. A portion of the concave diffraction grating (e.g., 140, 240) is depicted. The grooves (e.g., 145, 245) are etched or otherwise produced on the grating. The groove lines in this embodiment are not straight (i.e., curved) and are non-equally spaced. The grooves are generally non-parallel (although may be parallel and equally spaced for certain applications). The diffraction concave grating spatially disperses light by wavelengths of component colors (with each color diffracted along a distinct direction).

[0034] FIG. 6 schematically illustrates an exemplary three-detector system according to the invention, wherein the three detectors record wavelengths in the ranges of 520 nm - 380 nm, 380 nm - 240 nm, 240 nm - 170 nm, respectively. These are out-of-plane configurations. The spectral length of each wavelength range can be, for example, from about 15 mm to about 50 mm or longer.

[0035] FIG. 7 schematically illustrates an exemplary two-detector system according to the invention, wherein the two detectors record wavelengths in the ranges of 415 nm - 250 nm, 250 nm - 170 nm, respectively. These are out-of -plane configurations. The spectral length of each wavelength range can be, for example, from about 15 mm to about 50 mm or longer.

[0036] FIG. 8 schematically illustrates an exemplary three-detector system according to the invention, wherein the three detectors record wavelengths in the ranges of 520 nm - 380 nm, 380 nm - 240 nm, 240 nm - 170 nm, 170 nm - 125 nm, respectively. These are out-of - plane configurations. The spectral length of each wavelength range can be, for example, from about 15 mm to about 50 mm or longer.

[0037] FIG. 9 schematically illustrates an exemplary out- of- plane configuration, which has a large NA (0.6) and an assembly of aberration corrector. Out-of-plane configuration are are designed to maximize stray light reduction on the image plane. An exemplary

embodiment 900 of the optical system of the invention is shown in the y-z plane. The optical system 900 includes an entrance 910, which receives a radiation from a source object 904, which in general is not part of the optical system. An optical assembly 920 is in optical communication with the entrance 910 and is in optical communication with the aberration- corrected concave diffraction grating 940. An image plane 980 (for display, measurement or recording) is in optical communication with the aberration-corrected concave diffraction grating 940. The optical assembly 920 may include one, two or more optical lenses or devices. This configuration and related embodiments direct undesired light beams deflected from the grating away from the image plane, thereby minimizing the noise such deflected beams may cause.

[0038] FIG. 10 schematically illustrate an exemplary the tilted-in-plane configuration, which is also designed to minimize noise. An exemplary embodiment 1000 of the optical system of the invention is shown in the y-z plane. The optical system 1000 includes an entrance 1010, which receives a radiation from a source object 1004, which in general is not part of the optical system. An optical assembly 1020 is in optical communication with the entrance 1010 and is in optical communication with the aberration-corrected concave diffraction grating 1040. An image plane 1080 (for display, measurement or recording) is in optical communication with the aberration-corrected concave diffraction grating 1040. The optical assembly 1020 may include one, two or more optical lenses or devices. This configuration and related embodiments direct undesired light beams defiected from the grating away from the image area of the image plane, thereby minimizing the noise such deflected beams may cause.

[0039] The material and formation of the diffraction grating may be selected and accomplished dependent on the applications. Table 1 lists examples of materials useful for manufacturing of the diffraction gratings of the invention.

Table 1 Exemplary Materials useful for Manufacturing of Diffraction Gratings

Protective materials

Metal coatings

Photoresistant materials

Plastic, glass or metal substrate

[0040] A useful method for producing gratings is to use a diamond or similar tools to mechanically create the lines into the surface of the grating substrate such as a metal or plastic material. Mechanical ruling typically produces a grating having a triangular or staircase style cross-section. [0041] Photolithographic techniques allow gratings to be created from a holographic interference pattern. This is usually called holographic gratings. Holographic gratings have sinusoidal grooves and may not be as efficient as ruled gratings.

[0042] In one aspect, the invention generally relates to an optical system. The optical system includes: a plurality of optical entrances, each for receiving a radiation from a source object to be imaged; a first transmissive aberration corrector in optical communication with the plurality of entrances; an aberration-corrected concave diffraction grating in optical communication with the first transmissive aberration corrector, wherein the aberration- corrected concave diffraction grating includes a plurality of grooves that are non-parallel and unequally-spaced; a second transmissive aberration corrector in optical communication with aberration-corrected concave diffraction grating; and a plurality of image planes,

corresponding to the plurality of optical entrances respectively, each of the image planes is in optical communication with the second transmissive aberration corrector for recording a spectral image of the corresponding entrance. The radiation of the source object is refracted through the first transmissive aberration corrector, projected onto and diffracted from the aberration-corrected concave diffraction grating, refracted through the second transmissive aberration corrector before projected on to one of the plurality of image planes to form the spectral image.

[0043] In another aspect, the invention generally relates to a method for recording an optical image. The method includes: directing the radiation from a source object into a plurality of optical entrances; refracting the radiation through a first transmissive aberration corrector; projecting the refracted radiation onto an aberration-corrected concave diffraction grating thereby generating a diffracted radiation from the diffraction grating, wherein the aberration-corrected concave diffraction grating includes a plurality of grooves that are non- parallel and unequally-spaced; refracting the diffracted radiation through the second transmissive aberration corrector; and projecting the refracted radiation from the second transmissive aberration corrector on to a plurality of image planes to form spectral images.

[0044] In yet another aspect, the invention generally relates to a compact portable optical system. The compact portable optical system includes: three optical entrances, each for receiving a radiation from a source object to be imaged; a first transmissive aberration corrector in optical communication with the plurality of entrances; an aberration-corrected concave diffraction grating in optical communication with the first transmissive aberration corrector, wherein the aberration-corrected concave diffraction grating includes a plurality of grooves that are non-parallel and unequally-spaced; a second transmissive aberration corrector in optical communication with aberration-corrected concave diffraction grating; and three image planes, corresponding to the plurality of optical entrances respectively, each of the image planes is in optical communication with the second transmissive aberration corrector for recording a spectral image of the corresponding entrance. The radiation of the source object is refracted through the first transmissive aberration corrector, projected onto and diffracted from the aberration-corrected concave diffraction grating, refracted through the second transmissive aberration corrector before projected on to one of three image planes to form the spectral image. The optical system having a resolution is about 20 pm to about 100 pm.

[0045] The entrance is designed according to the application and is used to receive a radiation from the object source. The entrance may be a slit or an aperture of appropriate shape and dimension.

[0046] In certain embodiments, the first transmissive aberration corrector comprises a transparent block of material that is transmissive to radiation having a wavelength of from about 0.12 μιη to about 20 μιη. In certain embodiments of the optical system, the first transmissive aberration corrector comprises a transparent block of material that is

transmissive to radiation having a wavelength of from about 0.2 μιη to about 2.5 μιη.

[0047] In certain other embodiments the optical system, the second transmissive aberration corrector comprises a transparent block of material that is transmissive to radiation having a wavelength of from about 0.12 μιη to about 20 μιη. In certain embodiment of the optical system, the second transmissive aberration corrector comprises a transparent block of material that is transmissive to radiation having a wavelength of from about 0.2 μιη to about 2.5 μιη.

[0048] In some embodiments, the aberration-corrected concave diffraction grating includes non-parallel and unequally spaced grooves. In certain preferred embodiments, the aberration- corrected concave diffraction grating includes non-parallel and unequally spaced grooves having a density from about 50 lines/mm to about 3,000 lines/mm. In certain preferred embodiments, the aberration-corrected concave diffraction grating includes non-parallel and unequally spaced grooves having a density from about 200 lines/mm to about 2,000 lines/mm. [0049] The first and the second transmissive aberration corrector may be formed by a single lens or an optical assembly with a group of lenses. The surfaces of these lenses can be any suitable geometries, such as planar, spherical or aspherical.

[0050] Depending on the specific application and design, the first transmissive aberration corrector may include a flat or curved receiving surface that is in optical communication with the entrance.

[0051] Depending on the specific application and design, the first transmissive aberration corrector may include a curved output surface in optical communication with the aberration- corrected concave diffraction grating (although rarely the first transmissive aberration corrector could include a flat output surface in optical communication with the aberration- corrected concave diffraction grating).

[0052] Depending on the specific application and design, the second transmissive aberration corrector may include a curved receiving surface that is in optical communication with the grating (although rarely but in some embodiments, the second transmissive aberration corrector could include a flat receiving surface in optical communication with the grating).

[0053] Depending on the specific application and design, the second transmissive aberration corrector may include a flat or curved output surface in optical communication with the image plane.

[0054] The first and second transmissive aberration correctors may be made of MgF₂, UV grade fused silica, BK7 (Schott), Sapphire, CaF₂, Ge or Si (or a combination thereof), for example.

[0055] The aberration-corrected concave diffraction grating may include a plastic material, a glass material, metal (or a combination thereof).

[0056] In certain embodiments, the first and second transmissive aberration correctors each is proximally tilted towards the source object and distally tilted away from the source object. In certain embodiments, the first and second transmissive aberration correctors together forms a single transmissive aberration corrector.

[0057] In yet another aspect, the invention generally relates to an optical system. The optical system includes: a plurality of optical entrances, each for receiving a radiation from a source object to be imaged; a first optical assembly in optical communication with the plurality of entrances; an aberration-corrected concave diffraction grating in optical communication with the first optical assembly, wherein the aberration-corrected concave diffraction grating includes a plurality of grooves that are non-parallel and unequally-spaced; a second optical assembly in optical communication with aberration-corrected concave diffraction grating; and a plurality of image planes, corresponding to the plurality of optical entrances respectively, each of the image planes is in optical communication with the second optical assembly for recording a spectral image of the corresponding entrance. The radiation of the source object is refracted through the first optical assembly, projected onto and diffracted from the aberration-corrected concave diffraction grating, refracted through the second optical assembly before projected on to one of the plurality of image planes to form the spectral image.

[0058] In certain embodiments, the first optical assembly and the second optical assembly together forms a combined optical assembly comprising at least a transmissive aberration corrector. In certain embodiment, the combined optical assembly comprising two

transmissive aberration correctors.

[0059] Exemplary two detector optical system of the invention has the following specifications.

2 detector system:

F# of incident beam: 10.0

Entrance slit: 200 xlOum

Wavelength on detector 1 : 170nm to 250nm

wavelength on detector 2: 250nm to 415nm

diffraction (pm) 94 74 62 54

[0060] Exemplary three detector optical system of the invention has the following specifications.

3 detector system:

F# of incident beam: 10.0

Entrance slit: 200 xlOum

Wavelength on detector 1 : 170nm to 240nm

Wavelength on detector 2: 240nm to 380nm

Wavelength on detector 3: 380nm-520nm

spectral

length(mm) 28.66 35.59 39.73 50.16 maximum

FWHM(um) 12.4 15.7 16.51 13.03

Resolution from

raytrace(pm) 59 60 57 38

Resolution

considered

diffraction (pm) 90 85 79 54

[0061] The design flexibility of this invention may be accomplished through distance and angles between the components, radius of curvature of gratings, aberration corrector, materials of aberration corrector, etc. (See, e.g., Chapter 7 in "Diffraction Gratings" by M.C. Hutley; Chapter 7 in "Diffraction Gratings and Applications" by Erwin G. Loewen and Evgeny Popov.) The design of the optical systems may be designed by optical design software such as Zemax, Code V, etc.

[0062] Beneficial features of the optical systems and spectrometers of the invention include:

[0063] (1) The system includes an aberration-corrected concave grating, for example with non-equal spaced and curved fringe patterns. A particular fringe pattern (e.g., grooves) may be designed in association with the transmissive aberration corrector(s) for particular applications or utilities. This feature allows much more freedom and flexibility in the design and arrangement of the optical components in particular and the optical system in general. Additional geometric freedom and positioning options among the entrance slit, the aberration corrector(s), the concave grating, and the image recorder (or detector) enable the

spectrometers of the invention to provide unique functionalities and utilities. For example, the invention provides optical systems having high NA (numerical aperture) values.

[0064] (2) In common flat field concave grating, its flatness of spectral image plane and its spatial resolution is improved from those in Rowland gratings. But there are still not good enough, especially when the field of view increases. The optical system of the invention is superior to common flat field concave gratings in both spectral resolution and spatial resolution in large field of view.

[0065] (3) The optical systems of the invention offers superior dispersion than reflective Offner spectrometers, where dispersion cannot be large as the diffraction beam would be blocked by the convex grating if the dispersion of the grating increases beyond a pertain threshold. The optical systems of the invention are not so constrained. [0066] (4) The optical systems of the invention allow dimension flexibilities. For example, more compact imaging systems may be designed. Each image plane can be designed to have its own position and orientation to accommodate system design needs.

Incorporation by Reference

[0067] References and citations to other documents, such as patents, patent applications, patent publications, journals, books, papers, web contents, have been made in this disclosure. All such documents are hereby incorporated herein by reference in their entirety for all purposes.

Equivalents

[0068] The representative examples are intended to help illustrate the invention, and are not intended to, nor should they be construed to, limit the scope of the invention. Indeed, various modifications of the invention and many further embodiments thereof, in addition to those shown and described herein, will become apparent to those skilled in the art from the full contents of this document, including the examples disclosed and the references to the scientific and patent literature cited herein. The examples contain important additional information, exemplification and guidance which can be adapted to the practice of this invention in its various embodiments and equivalents thereof.

What is claimed is:

Claims

1. An optical system, comprising: a plurality of optical entrances, each for receiving a radiation from a source object to be imaged; a first transmissive aberration corrector in optical communication with the plurality of entrances; an aberration-corrected concave diffraction grating in optical communication with the first transmissive aberration corrector, wherein the aberration-corrected concave diffraction grating includes a plurality of grooves that are non-parallel and unequally-spaced; a second transmissive aberration corrector in optical communication with aberration- corrected concave diffraction grating; and a plurality of image planes, corresponding to the plurality of optical entrances respectively, each of the image planes is in optical communication with the second transmissive aberration corrector for recording a spectral image of the corresponding entrance, wherein the radiation of the source object is refracted through the first transmissive aberration corrector, projected onto and diffracted from the aberration-corrected concave diffraction grating, refracted through the second transmissive aberration corrector before projected on to one of the plurality of image planes to form the spectral image.

2. The optical system of Claim 1, wherein the plurality of optical entrances are two optical entrances and wherein the plurality of image planes are two image planes.

3. The optical system of Claim 1, wherein the plurality of optical entrances are three optical entrances and wherein the plurality of image planes are three image planes.

4. The optical system of Claim 1, wherein the plurality of optical entrances are four or more optical entrances and wherein the plurality of image planes are four image planes.

5. The optical system of Claim 2, wherein the two image planes record wavelength ranges of from about 170 nm to about 250 nm and from about 250 nm to about 415 nm, respectively.

6. The optical system of Claim 3, wherein the three image planes record wavelength ranges from about 170 nm to about 240 nm, from about 240 nm to about 380 nm, and from about 380 nm to about 520 nm, respectively.

7. The optical system of Claim 4, wherein the four image planes record wavelength ranges from about 125 nm to about 170 nm, from about 170 nm to about 240 nm, from about 240 nm to about 380 nm, and from about 380 nm to about 520 nm, respectively.

8. The optical system of Claim 1, wherein the aberration-corrected concave diffraction grating comprises non-parallel and unequally spaced grooves having a density from about 50 lines/mm to about 3,000 lines/mm.

9. The optical system of Claim 8, wherein the aberration-corrected concave diffraction grating comprises non-parallel and unequally spaced grooves having a density from about 200 lines/mm to about 2,000 lines/mm.

10. The optical system of Claim 1 having an optical resolution of about 20 pm to about 100 pm.

11. The optical system of Claim 1 , wherein the first and second transmissive aberration correctors are made of MgF₂, UV grade fused silica, standard grade fused silica, BK7 (Schott), Sapphire, CaF₂, Ge or Si.

12. The optical system of Claim 1, wherein the first and second transmissive aberration correctors are made of UV grade fused silica or BK7.

13. The optical system of Claim 1, wherein the aberration-corrected concave diffraction grating comprises a photoresistant material.

14. The optical system of Claim 1, wherein the aberration-corrected concave diffraction grating comprises a metal coating.

15. The optical system of Claim 1, wherein the aberration-corrected concave diffraction grating comprises a protective layer.

16. The optical system of Claim 1, wherein the first and second transmissive aberration correctors each is proximally tilted towards the source object and distally tilted away from the source object.

17. The optical system of Claim 16, wherein the first and second transmissive aberration correctors together forms a single transmissive aberration corrector.

18. A method for recording an optical image, comprising: directing the radiation from a source object into a plurality of optical entrances; refracting the radiation through a first transmissive aberration corrector; projecting the refracted radiation onto an aberration-corrected concave diffraction grating thereby generating a diffracted radiation from the diffraction grating, wherein the aberration-corrected concave diffraction grating includes a plurality of grooves that are non- parallel and unequally-spaced; refracting the diffracted radiation through the second transmissive aberration corrector; and projecting the refracted radiation from the second transmissive aberration corrector on to a plurality of image planes to form spectral images.

19. The optical system of Claim 18, wherein the plurality of optical entrances are two optical entrances and wherein the plurality of image planes are two image planes.

20. The optical system of Claim 18, wherein the plurality of optical entrances are three optical entrances and wherein the plurality of image planes are three image planes.

21. The optical system of Claim 18, wherein the plurality of optical entrances are four optical entrances and wherein the plurality of image planes are four image planes.

22. The optical system of Claim 18, wherein the two image planes record wavelength ranges of from about 170 nm to about 250 nm and from about 250 nm to about 415 nm, respectively.

23. The optical system of Claim 20, wherein the three image planes record wavelength ranges from about 170 nm to about 240 nm, from about 240 nm to about 380 nm, and from about 380 nm to about 520 nm, respectively.

24. The method of Claim 18, wherein the radiation comprises a wavelength from about 0.12 μιη to about 20 μιη.

25. The method of Claim 18, wherein the radiation comprises a wavelength from about 0.2 μιη to about 2.5 μιη.

26. The method of Claim 18, wherein the transmissive aberration corrector is made of MgF₂, UV grade fused silica, BK7, Sapphire, CaF₂, Ge or Si.

27. The method of Claim 26, wherein the transmissive aberration corrector is made of UV grade fused silica or BK7.

28. The method of Claim 18, wherein the aberration-corrected concave diffraction grating comprises a photoresistant material.

29. The method of Claim 28, wherein the aberration-corrected concave diffraction grating comprises a metal coating.

30. The method of Claim 28, wherein the aberration-corrected concave diffraction grating comprises a protective layer.

31. The method of Claim 18, wherein the aberration-corrected concave diffraction grating includes a plurality of grooves that are non-parallel and unequally-spaced.

32. A compact portable optical system, comprising: three optical entrances, each for receiving a radiation from a source object to be imaged; a first transmissive aberration corrector in optical communication with the plurality of entrances; an aberration-corrected concave diffraction grating in optical communication with the first transmissive aberration corrector, wherein the aberration-corrected concave diffraction grating includes a plurality of grooves that are non-parallel and unequally-spaced; a second transmissive aberration corrector in optical communication with aberration- corrected concave diffraction grating; and three image planes, corresponding to the plurality of optical entrances respectively, each of the image planes is in optical communication with the second transmissive aberration corrector for recording a spectral image of the corresponding entrance, wherein the radiation of the source object is refracted through the first transmissive aberration corrector, projected onto and diffracted from the aberration-corrected concave diffraction grating, refracted through the second transmissive aberration corrector before projected on to one of three image planes to form the spectral image, wherein the optical system having a resolution is about 20 pm to about 100 pm.

33. An optical system, comprising: a plurality of optical entrances, each for receiving a radiation from a source object to be imaged; a first optical assembly in optical communication with the plurality of entrances; an aberration-corrected concave diffraction grating in optical communication with the first optical assembly, wherein the aberration-corrected concave diffraction grating includes a plurality of grooves that are non-parallel and unequally-spaced; a second optical assembly in optical communication with aberration-corrected concave diffraction grating; and a plurality of image planes, corresponding to the plurality of optical entrances respectively, each of the image planes is in optical communication with the second optical assembly for recording a spectral image of the corresponding entrance, wherein the radiation of the source object is refracted through the first optical assembly, projected onto and diffracted from the aberration-corrected concave diffraction grating, refracted through the second optical assembly before projected on to one of the plurality of image planes to form the spectral image.

34. The optical system of Claim 33, wherein the first optical assembly and the second optical assembly together forms a combined optical assembly comprising at least a transmissive aberration corrector.

35. The optical system of Claim 34, wherein the combined optical assembly comprising two transmissive aberration correctors.