A low-resolution dual-channel long-slit spectrograph system for an astronomical telescope and an imaging method thereof

Abstract

This invention discloses a low-resolution dual-channel long-slit spectrometer system and its imaging method for astronomical telescopes, belonging to the field of astronomical spectroscopic detection technology. The system includes a slit arranged along the optical path, a field lens, a dichroic cemented prism module, and collimating optical systems, dispersive gratings, imaging optical systems, and focal planes corresponding to the blue and red channels, respectively. The dichroic cemented prism module splits the incident beam into blue and red channels, which are then collimated, dispersed by the grating, and focused onto their respective focal planes after imaging. The blue and red channel focal planes are tilted along the spectral direction to compensate for chromatic aberration. This invention can achieve single-exposure coverage of a continuous wide wavelength range of 360nm to 985nm, with a spectral resolution of less than 1000 and a field of view greater than 3 arcminutes. It combines high system efficiency, compact structure, and low development cost, meeting the spectral observation needs of temporal astronomical transient sources and surface source targets.

Description

Technical Field

[0001] This invention belongs to the field of astronomical spectroscopic detection technology, and particularly relates to a low-resolution dual-channel long-slit spectrometer system for astronomical telescopes and its imaging method. Background Technology

[0002] Spectroscopic observations of time-domain astronomical transient sources are crucial tools in astronomical research, serving as key tools for decoding violent cosmic events, discovering entirely new physical phenomena, and expanding our understanding of the universe. These observations typically target extremely faint objects, demanding exceptionally high spectrometer efficiency. For example, telescopes based on the 2-meter class often require limiting magnitudes higher than 21. Furthermore, transient sources are celestial objects that change rapidly over time, requiring a single exposure to cover a broad spectral range from 360 nm in the ultraviolet to 985 nm in the near-infrared. Additionally, their spectral resolution is typically low, only a few hundred nm; to observe emerging sources such as galaxies, a field of view greater than 3 arcminutes is required to cover the vast majority of emerging sources. Moreover, the astronomical spectrometer is mounted at the telescope's focal point, and as the spectrometer rotates with the telescope, a compact optical path layout is usually necessary to minimize gravitational distortion.

[0003] Traditional spectrometers are mostly CT-structured reflective spectrometers, which are typically equipped with multiple gratings of varying line densities. By rotating or replacing the gratings, multiple exposures are performed to achieve full-band coverage of the observed spectrum.

[0004] For example, patent application number: CN202510429905.9.

[0005] Echo grating spectrometers utilize the high diffraction orders of echelle gratings to achieve full-spectrum coverage. These spectrometers employ cross-dispersion (typically using prisms or gratings as secondary dispersive elements) to expand different diffraction orders on a two-dimensional detector, allowing for the acquisition of broad-band spectral information in a single exposure, as illustrated in patent: 202411129095.7. The aforementioned existing technical solutions all have obvious limitations and are difficult to meet the special requirements of time-domain astronomical transient source observation: Traditional CT-type spectrometers typically employ multiple gratings of varying line densities, requiring multiple exposures to achieve full-spectrum coverage. However, this approach struggles to meet the real-time requirements of transient source observations. Reflective blazed gratings are difficult to deploy in Littrow mode, reducing the overall efficiency of both the grating and the spectrometer. While spectrometers based on echelle gratings can achieve full-spectrum coverage through multiple gratings, their field of view is relatively small, limiting their application to point source observations. Furthermore, their high spectral resolution makes them suitable for medium- to high-resolution spectral observations, thus reducing the observed magnitude.

[0006] In summary, existing spectrometer technologies are insufficient in terms of wide-band single-shot coverage, large field-of-view source observation capabilities, system efficiency, and structural compactness, making it difficult to simultaneously meet the comprehensive requirements of time-domain astronomical transient source observation for low resolution, wide band, large field of view, high efficiency, and real-time performance. Summary of the Invention

[0007] The purpose of this invention is to provide a low-resolution dual-channel long-slit spectrometer system and its imaging method for astronomical telescopes. This system aims to address the limitations of astronomical telescope spectroscopic instruments in meeting the demands for wide-band coverage and high efficiency, while also maintaining a compact structure. Through the coordinated design of a dual-channel beam-splitting architecture and a transmission optical system, it achieves continuous wide-band spectral detection from ultraviolet to near-infrared in a single exposure, while also being compatible with large-view surface source target observations. Furthermore, it achieves high system efficiency, excellent imaging quality, and a compact optical path layout to meet the spectroscopic observation requirements of temporal astronomical transient sources and surface source targets.

[0008] To achieve the above-mentioned objectives, this invention provides a low-resolution dual-channel long-slit spectrometer system for astronomical telescopes, the complete technical solution of which is as follows.

[0009] A low-resolution long-slit spectrometer for astronomical telescopes includes a slit arranged along the optical path, a field lens, a dichroic cemented prism, a blue channel collimating optical system, a blue channel dispersion grating, a blue channel imaging optical system and a blue channel focal plane, a red channel collimating optical system, a red channel dispersion grating, a red channel imaging optical system and a red channel focal plane.

[0010] The slit is positioned on the focal plane of the telescope, and simultaneously on the focal planes of both the blue channel collimating optical system and the red channel collimating optical system, to limit the field of view of the incident beam. The slit is elongated, with its width selected between 0.5 arcseconds and 5.0 arcseconds based on the atmospheric seeing requirements of the site and the target's spectral resolution. Its length corresponds to a field of view greater than 3 arcminutes to meet the observation requirements of surface-source (extended-source) targets.

[0011] The field lens is positioned on the exit light path of the slit and is used to control the exit pupil positions of the blue channel collimating optical system and the red channel collimating optical system, ensuring that the exit pupil position is located behind the last lens of the collimating system, thus reserving space for the structural envelope installation of the blue channel dispersion grating and the red channel dispersion grating. The field lens is a plano-convex positive lens made of fused silica material with low ultraviolet absorption.

[0012] The dichroic cemented prism module is disposed and cemented tightly with the exit optical path of the field lens, and is used to split the incident beam into a blue channel beam and a red channel beam, which exit in different directions. Specifically, the dichroic cemented prism module includes a parallelogram prism and a folding optical path prism, and the cemented surfaces of the two are coated with a dichroic film. The blue channel beam is reflected at the cemented surface and exits from the parallelogram prism, while the red channel beam is transmitted through the cemented surface and exits from the folding optical path prism. The parallelogram prism is used to make the exit direction of the blue channel beam parallel to the direction of the incident beam, and the folding optical path prism is used to make the exit direction of the red channel beam parallel to the direction of the incident beam. The color-separating cemented prism module uses fused silica material with low ultraviolet absorption. By controlling the geometric dimensions of the parallelogram prism and the folding optical path prism, the center interval between the emitted beams from the blue channel and the red channel can be controlled, reserving space for the optical-mechanical structure design and camera installation, and avoiding structural interference.

[0013] The blue channel operates in the wavelength range of 360nm to 625nm, and the red channel operates in the wavelength range of 600nm to 985nm. The blue channel and the red channel form a transition zone in the 600nm to 625nm wavelength range, thereby achieving a continuous wide wavelength range of 360nm to 985nm in a single exposure.

[0014] The blue channel collimating optical system is positioned on the blue channel output light path of the dichroic cemented prism module, and is used to convert the blue channel beam into a collimated beam. It includes a blue channel collimating lens, a blue channel collimating lens, and a blue channel collimating lens arranged sequentially along the light path. The blue channel collimating lenses are negative meniscus lenses, and the blue channel collimating lens is a biconvex positive lens. The blue channel collimating lens, together with the field lens and the parallelogram prism, constitutes a blue channel transmission collimating optical system, whose focal ratio is the same as the incident focal ratio (F#=5~9) of the telescope. All blue channel collimating lenses are made of i-line glass material or optical crystal material with low ultraviolet absorption (e.g., PBM2Y, BSL7Y, CaF2).

[0015] The blue channel dispersion grating is positioned in the exit optical path of the blue channel collimating optical system and at its exit pupil, used to disperse the collimated beam of the blue channel. The blue channel dispersion grating consists of two prisms and a volume phase holographic grating (VPH grating) sandwiched between them. The two prisms have the same apex angle, which matches the center wavelength of the blue channel, ensuring that the blue channel dispersion grating operates at the Littrow incident angle, where diffraction efficiency is highest. Furthermore, the diffraction angle at the center wavelength of the blue channel is parallel to the incident angle, thus making the diffracted beam within the blue channel's operating wavelength symmetrical about the center wavelength. The blue channel dispersion grating is made of fused silica with low absorption in the ultraviolet band. The line density of its volume phase holographic grating is customized to match the target spectral resolution (e.g., 430 lines / mm).

[0016] The blue channel imaging optical system is positioned on the outgoing light path of the blue channel dispersive grating and is used to image the dispersed blue channel beam onto the blue channel focal plane. It includes, sequentially and closely connected along the optical path, a blue channel imaging lens, a blue channel imaging lens, a blue channel imaging lens, a blue channel imaging lens, a blue channel camera vacuum sealing glass. The blue channel imaging lenses are biconvex positive lenses, and the blue channel imaging lenses are meniscus lenses. The entrance pupil of the blue channel imaging optical system is located on the diffraction surface of the blue channel dispersive grating. The blue channel imaging lens uses a low-absorption ultraviolet i-line glass material or optical crystal material (e.g., S-FPL53, BSM51Y, PBM8Y, BAL35Y, etc.).

[0017] The blue channel focal plane is used to mount a scientific-grade CCD camera, the quantum efficiency curve of which matches the operating wavelength of the blue channel. The vacuum-sealed window glass of the blue channel camera is used to achieve vacuum sealing and deep cooling below -70°C for the scientific-grade CCD camera, thereby reducing dark current noise in the detector. The blue channel focal plane is tilted relative to the optical axis of the blue channel imaging optical system along the spectral dispersion direction (tilt angle less than 4°, e.g., 3.565°) to compensate for residual chromatic aberration in the blue channel imaging optical system, reduce the design complexity of the imaging optical system, and improve spectral imaging quality.

[0018] The red channel collimating optical system is positioned on the red channel exit optical path of the dichroic cemented prism module, and is used to convert the red channel beam into a collimated beam. It includes a red channel collimating lens, a red channel collimating lens, and a red channel collimating lens arranged sequentially along the optical path. The red channel collimating lenses are negative meniscus lenses, and the red channel collimating lens is a biconvex positive lens. The red channel collimating lens, together with the field lens and the folding prism, constitutes a red channel transmission collimating optical system, with a focal ratio identical to the incident focal ratio of the telescope (F#=5~9). All red channel collimating lenses utilize low-absorption optical materials within the operating wavelength range (e.g., PBM2Y, BSL7Y, CaF2).

[0019] The red channel dispersion grating is disposed in the exit optical path of the red channel collimating optical system and located at its exit pupil position, for dispersing the red channel collimated beam. The red channel dispersion grating consists of two prisms and a volume phase holographic grating (VPH grating) sandwiched between them. The two prisms have the same apex angle, which matches the center wavelength of the red channel, ensuring that the red channel dispersion grating operates at a Litterrow incident angle, and that the diffraction angle at the center wavelength of the red channel is parallel to the incident angle, thus making the diffracted beam within the red channel operating band symmetrical about the center wavelength. The material of the red channel dispersion grating is a low-absorption fused silica material within the operating band. The line density of its volume phase holographic grating is customized to match the target spectral resolution (e.g., 330 lines / mm).

[0020] The red channel imaging optical system is positioned on the outgoing light path of the red channel dispersive grating and is used to image the dispersed red channel beam onto the red channel focal plane. It includes, sequentially and closely arranged along the optical path, a red channel imaging lens, a red channel imaging lens, a red channel imaging lens, a red channel imaging lens, a red channel camera vacuum sealing glass. The first and second red channel imaging lenses are biconvex positive lenses, while the third and fourth red channel imaging lenses are meniscus lenses. The entrance pupil of the red channel imaging optical system is located on the diffraction surface of the red channel dispersive grating. The red channel imaging lenses utilize low-absorption optical materials within the operating wavelength range (e.g., S-FPL53, S-LAH51, PBM2Y, S-LAH58, S-LAL54, etc.).

[0021] The red channel focal plane is used to mount a deep-depletion scientific-grade CCD camera. The quantum efficiency curve of the deep-depletion scientific-grade CCD camera is matched with the operating wavelength of the red channel to improve the detection efficiency in the near-infrared band. The vacuum sealing glass of the red channel camera is used to achieve vacuum sealing and deep cooling below -70°C for the deep-depletion scientific-grade CCD camera. The red channel focal plane is tilted relative to the optical axis of the red channel imaging optical system along the spectral dispersion direction (tilt angle less than 4°, for example, 0.975°) to compensate for the residual chromatic aberration of the red channel imaging optical system.

[0022] The blue channel grating line density is custom-matched to the spectral resolution. The spectral resolution satisfies the following relationship: in, The Littoral angle of the blue channel dispersion grating or the red channel dispersion grating. This refers to the focal length of the corresponding channel collimating optical system. The physical width of the slit is given.

[0023] This invention also provides a low-resolution broadband long-slit spectral imaging method for astronomical spectroscopic observations, characterized by employing the aforementioned low-resolution dual-channel long-slit spectrometer system, comprising the following steps: Step 1: The incident beam from the telescope is limited to the field of view by the slit and then enters the field lens; Step 2: The beam emitted from the field lens enters the dichroic cemented prism module, where the incident beam is split into a blue channel beam and a red channel beam at the cemented surface. The blue channel beam is reflected and then emitted from the dichroic cemented prism module, while the red channel beam is transmitted and then emitted from the dichroic cemented prism module. Step 3: The blue channel beam is collimated by the blue channel collimating optical system, dispersed by the blue channel dispersive grating, and imaged by the blue channel imaging optical system in sequence, and then focused on the blue channel focal plane; at the same time, the red channel beam is collimated by the red channel collimating optical system, dispersed by the red channel dispersive grating, and imaged by the red channel imaging optical system in sequence, and then focused on the red channel focal plane. Step four: Collect blue channel spectral data and red channel spectral data respectively through detectors set at the blue channel focal plane and the red channel focal plane, and stitch the two channel data together to obtain complete spectral data covering a wide band of 360nm to 985nm under a single exposure.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: In this application, the observation spectrum of the long-slit spectrometer is divided into red and blue channels by using a dichroic prism. A single exposure can cover a wide spectral range from ultraviolet to near-infrared, meeting the real-time requirements of astronomical transient sources for spectral observation.

[0025] Divided into red and blue channels, the collimating optical system, dispersive grating, imaging optical system and detector of each channel can be designed and matched specifically, which improves the average efficiency in the red and blue bands and meets the requirements of astronomical spectrometers for observing limiting magnitudes.

[0026] By using two small-panel scientific cameras, full-band coverage can be achieved, reducing the development cost of the spectrometer.

[0027] The color separation element is designed as a cemented prism, the dispersive element adopts a prism grating design, the incident beam and the diffracted beam are designed to be on the same optical axis, and the collimation and imaging spectrum adopt a transmission optical system design. The structure is symmetrical and compact, which is beneficial to the mechanical structure design and reduces the gravitational deformation of the spectrometer, resulting in better stability. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the optical path structure of a dual-channel slit spectrometer provided in an embodiment of this application; Figure 2 This is a schematic diagram of the installation of the device at the focal point of a 2-meter telescope according to an embodiment of this application; Figure 3 This is a schematic diagram of the field mirror and prism color separation unit in an embodiment of this application; Figure 4 This is a schematic diagram of the blue channel optical path structure in the embodiments of this application; Figure 5 This is a schematic diagram of the blue channel collimating optical system structure in the embodiments of this application; Figure 6 This is a schematic diagram of the blue channel imaging optical system structure in an embodiment of this application; Figure 7 This is a schematic diagram of the blue channel prism in an embodiment of this application; Figure 8 This is a schematic diagram of the red channel optical path structure in an embodiment of this application; Figure 9 This is a schematic diagram of the red channel collimating optical system structure in the embodiments of this application; Figure 10 This is a schematic diagram of the red channel imaging optical system structure in an embodiment of this application; Figure 11This is a schematic diagram of the red channel prism provided in the embodiments of this application; Figure 12 This is a curve showing the change in blue channel RMS diffusion spot size with wavelength in an embodiment of this application.

[0030] Figure 13 This is a curve showing the change in the size of the red channel RMS diffusion spot as a function of wavelength in an embodiment of this application.

[0031] Figure 14 This is the blue channel diffusion speckle matrix in the embodiments of this application.

[0032] Figure 15 This is the red channel diffusion speckle matrix in the embodiments of this application.

[0033] Figure 16 The figures show the spectral resolution curves of the red and blue channels in the embodiments of this application.

[0034] In the picture: Detailed Implementation The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0035] In the description of this application, it should be noted that, unless otherwise stated, "multiple" means two or more; the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicating orientation or positional relationships are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific manner, and therefore should not be construed as limiting the application. Furthermore, the terms "first," "second," and "third," etc., are only used to describe within permissible ranges. "Parallel" is not parallel in the strict sense, but rather within the permissible range of error.

[0036] To better understand this application, the characteristics of the spectrometer as "low resolution", "wide band" and "long slit spectrometer" will be briefly described first.

[0037] "Low resolution" mainly refers to a spectral resolution of approximately 0.5 nm to 1 nm. The term "wideband" specifically refers to a single exposure that can cover the near-infrared band from 310nm ultraviolet to 1100nm.

[0038] The term "long slit spectrometer" specifically refers to a spectrometer whose entrance slit is a long strip-shaped field of view along the spectral spatial direction.

[0039] This application provides a dual-channel long-slit spectrometer for astronomical telescopes, the optical path structure of which is as follows: Figure 1 As shown. The spectrometer is fixedly mounted at the focal point of the telescope (e.g., Figure 2 As shown), its entrance slit 1 is placed on the focal plane of the telescope, and simultaneously on the object-side focal plane of the subsequent blue and red channel collimating optical systems.

[0040] It includes a slit 1 set along the optical path, a field lens 2, a dichroic cemented prism 3, a blue channel collimating optical system, a blue channel dispersion grating 7, a blue channel imaging optical system and a blue channel focal plane 14, a red channel collimating optical system, a red channel dispersion grating 19, a red channel imaging optical system and a red channel focal plane 26.

[0041] like Figure 1 As shown, the low-resolution long-slit spectrometer, after passing through slit 1 and field lens 2, uses a dichroic prism module to divide the observed spectral band into red and blue channels. The blue channel reflects the light, while the red channel transmits it. The beam reflected from the blue channel is reflected again by the prism and becomes parallel to the incident beam from the telescope; the transmitted beam from the red channel is also reflected twice by the prism surface and becomes parallel to the incident beam. The beam exiting the dichroic prism module becomes a parallel beam after passing through the blue channel collimating optical system and the red channel collimating optical system. The blue channel dichroic grating and the red channel dichroic grating are located on the exit pupil surfaces of the blue channel and red channel collimating optical systems, respectively. The beam dispersed by the gratings is then imaged onto the focal plane of the spectrometer by the blue channel imaging system and the red channel imaging system, respectively.

[0042] like Figure 2 As shown, optionally, a schematic diagram of the optical path of the slit spectrometer installed at the focal point of a 2-meter telescope is presented. The slit 1 of the slit spectrometer is located at the focal plane of the telescope, and simultaneously at the focal point of the blue channel collimating optical system and the red channel collimating optical system.

[0043] In the embodiments of this application, the incident focal ratio F# of the telescope is mostly between 5 and 9. Figure 2 In the illustrated embodiment, the telescope has an aperture of 2 meters and a focal ratio of F6.

[0044] In some embodiments, the slit width is optional from 0.5 arcsec to 5.0 arcsec, and the slit length is 6.94 arcmin.

[0045] In this embodiment, the field lens 2 is located in the slit and is glued tightly to the dichroic prism module. It is used to control the exit pupil position of the blue channel collimating optical system and the red channel collimating optical system. The exit pupil position is located after the last lens of the collimating system, and the structural envelope installation position of the blue channel dispersion grating 7 and the red channel dispersion grating 19 is expected.

[0046] In this embodiment, the field lens is a plano-convex positive lens, and optionally, the optical material is fused silica.

[0047] In some embodiments, the exit pupil of the blue channel collimation system is located at -27.44 mm in front of the last lens of the blue channel collimation system; the exit pupil of the red channel collimation system is located at 24.47 mm in front of the last lens of the red channel collimation system.

[0048] The dichroic prism module is located close to the right side of field lens 2; the blue channel reflected beam is folded 90 degrees and transmitted upwards, and after passing through a 45-degree folding mirror, its propagation direction is parallel to the incident beam; the red channel transmitted beam propagates along the original optical path, and after passing through a 45-degree folding mirror, its direction is deviated by 90 degrees from the incident beam, and after passing through another 45-degree folding mirror, the red channel transmitted beam is parallel to the incident beam.

[0049] In this embodiment, the color-separating prism module is formed by bonding a parallelogram prism 3 and a folding optical path prism 15 together. A color-separating film is coated on the bonding surface of the parallelogram prism 3 and the folding optical path prism 15 to achieve the separation of red and blue channels.

[0050] In some embodiments, the dichroic center wavelength of the dichroic film is 612.5 nm, with the blue channel reflecting light from 360 nm to 625 nm and the red channel transmitting light from 600 nm to 985 nm. The 600 nm to 625 nm band is the transition band of the dichroic film. This transition band occurs because, when the dichroic film is incident at a certain angle, the reflection initiation wavelengths of S-polarized light and P-polarized light are different, causing the dichroic film to gradually increase from reflection to transmission.

[0051] The adhesive bonding design of the dichroic prism module reduces the difficulty of assembling and adjusting the optical path of the spectrometer. By controlling the size of the parallelogram prism and the folding optical path prism, the dichroic prism module controls the distance between the red and blue channels, reserving structural space for the optomechanical structure design and camera installation, avoiding structural interference. It also provides sufficient distance for the collimation and imaging mechanical support structure design and camera installation, preventing interference between the red and blue channels.

[0052] In some embodiments, such as Figure 3 As shown, the center-to-center distance between the beams emitted from the blue channel dichroic prism and the red channel dichroic prism is 80 mm.

[0053] In the embodiments of this application, such as Figure 5As shown, the blue channel collimating optical system is located after the blue colorimetric prism and is a transmission optical system, including blue channel collimating lens 4, blue channel collimating lens 5, and blue channel collimating lens 6. Blue channel collimating lenses 4, 5, and 6 are connected sequentially. Together with field lens 1 and blue colorimetric prism 3, blue channel collimating lenses 4, 5, and 6 form a blue channel transmission collimating optical system, which deforms the diverging beam exiting the slit into parallel light.

[0054] In this embodiment, the focal ratio of the blue channel transmission collimating optical system is the same as the incident focal ratio of the telescope; in some embodiments, the focal ratio of the blue channel collimating system is F6, or any value between F4 and F12. The focal length of the red channel collimating optical system can be the same as or different from that of the blue channel. In some embodiments, the focal length of the collimating system is 183.6 mm, and the exit pupil diameter of the collimating system is 30.6 mm.

[0055] The blue channel collimating lens 4, blue channel collimating lens 5 and blue channel collimating lens 6 in the blue channel collimating optical system are all made of i-line glass material with low ultraviolet absorption.

[0056] In some embodiments, the optical materials of the blue channel lens 4, the blue channel collimating lens 5, and the blue channel collimating lens are PBM2Y, BSL7Y, and CaF2 materials.

[0057] In this embodiment, the blue channel collimating lens 4 and blue channel collimating lens 5 are negative meniscus lenses, and the blue channel collimating lens 6 is a biconvex positive lens.

[0058] In some embodiments, the focal length of the blue channel collimating lens 4 is -153.89mm, the focal length of the blue channel collimating lens 5 is -91.49mm, and the focal length of the blue channel collimating lens 6 is 58.82mm.

[0059] In the embodiments of this application, such as Figure 7 As shown, the blue channel dispersive grating 7 is located at the pupil plane of the collimated beam in the blue channel. The blue channel dispersive grating consists of two prisms and a volume-phase holographic grating. The apex angle of the prisms matches the center wavelength of the blue channel, allowing the blue channel grating to operate at the Littoral angle of incidence, where diffraction efficiency is highest. The diffraction angle at the center wavelength of the blue channel is parallel to the incident angle, ensuring symmetry of the diffracted beam about the center wavelength within the blue channel's operating band. The identical apex angles of the two prisms in the blue channel grating facilitate optical fabrication.

[0060] In some embodiments, the apex angle of the blue channel prism is 13.06 degrees, and the prism material is fused silica. The volume phase holographic grating has a line density of 430 lines per millimeter.

[0061] In the embodiments of this application, such as Figure 6As shown, the blue channel imaging system, located after the blue channel dispersive grating, comprises blue channel imaging lenses 8, 9, 10, 11, and 12, and a blue channel camera plane window 13. These lenses are sequentially connected along the beam propagation path. The entrance pupil of the blue channel imaging system is located on the diffraction surface of the blue channel dispersive grating.

[0062] In this embodiment, the blue channel imaging system is a transmission optical system, and the lens materials used are all i-line glass or optical crystal materials, which reduces the internal absorption of the optical materials and improves the overall transmittance of the spectrometer.

[0063] In some embodiments, the materials of blue channel imaging lens 8, blue channel imaging lens 9, blue channel imaging lens 10, blue channel imaging lens 11, and blue channel imaging lens 12 are S-FPL53, BSM51Y, PBM8Y, BAL35Y, and BSM51Y, respectively.

[0064] In this embodiment, blue channel imaging lens 8 and blue channel imaging lens 11 are positive biconvex lenses; blue channel imaging lens 9, blue channel imaging lens 10, and blue channel imaging lens 12 are meniscus lenses. In some embodiments, the blue channel imaging system has a focal length of 98.5 mm. Blue channel imaging lens 8 has a focal length of -65.66 mm; blue channel imaging lens 9 has a focal length of 97.31 mm; blue channel imaging lens 10 has a focal length of -111.07 mm; blue channel imaging lens 11 has a focal length of 45.74 mm; and blue channel imaging lens 12 has a focal length of -73.88 mm.

[0065] In this embodiment, the blue channel imaging lens 13 is the vacuum sealing glass of the blue channel camera, which realizes the vacuum sealing of the detector and the deep cooling of the detector below -70°C, thereby reducing the dark current noise of the detector.

[0066] In this embodiment, the focal plane of the blue channel detector is used to mount a scientific-grade CCD camera; the quantum effect curve of the scientific-grade CCD camera matches the working band of the blue channel, achieving high efficiency within the working band. The focal plane of the blue channel detector is tilted at an angle of less than 4 degrees along the spectral direction to compensate for the chromatic aberration of the blue channel imaging system, reduce the complexity of the blue channel imaging optical system, and improve the spectral imaging quality.

[0067] In some embodiments, the scientific-grade CCD camera has 1024×1024 pixels and a pixel size of 13µm. The detector is tilted at an angle of 3.565 degrees along the spectral direction.

[0068] In the embodiments of this application, such as Figure 9 As shown, the red channel collimating optical system is located after the red channel folding prism and includes red channel collimating lens 16, red channel collimating lens 17, and red channel collimating lens 18. Red channel collimating lenses 16, 17, and 18 are connected sequentially. Together with field lens 1 and red channel folding dichroic prism 3, red channel collimating lenses 16, 17, and 18 form a red channel transmission collimating optical system, which deforms the diverging beam exiting the slit into parallel light.

[0069] In this embodiment, the focal ratio of the red channel transmission collimating optical system is the same as the incident focal ratio of the telescope; in some embodiments, the focal ratio of the red channel collimating system is F6, or any value between F4 and F12. In some embodiments, the focal length of the collimating system is 183.6 mm, and the exit pupil diameter of the collimating system is 30.6 mm.

[0070] In this embodiment, the red channel collimating lens 16, red channel collimating lens 17, and red channel collimating lens 18 all employ optical materials with low absorption within the operating wavelength band. In some embodiments, the optical materials of the red channel collimating lens 16, red channel collimating lens 17, and red channel collimating lens 18 are PBM2Y, BSL7Y, and CaF2, or corresponding non-i-line glass materials of the same grade may be selected.

[0071] In this embodiment, the red channel collimating lens 16 and 17 are negative meniscus lenses, and the red channel collimating lens 18 is a biconvex positive lens. In some embodiments, the focal length of the red channel collimating lens 16 is -131.56mm, the focal length of the red channel collimating lens 17 is -166.3mm, and the focal length of the red channel collimating lens 18 is 73.1mm.

[0072] In the embodiments of this application, such as Figure 11 As shown, the red channel dispersive grating consists of two prisms and a volume phase holographic grating. The apex angle of the prisms matches the center wavelength of the red channel, allowing the red channel grating to operate at the Littoral angle of incidence, where diffraction efficiency is highest. The diffraction angle at the center wavelength of the red channel is parallel to the angle of incidence, ensuring that the diffracted beam is symmetrical about the center wavelength within the red channel's operating band. The identical apex angles of the two prisms in the red channel grating facilitate optical fabrication.

[0073] In some embodiments, the apex angle of the red channel prism is 16.24 degrees, and the prism material is fused silica. The volume phase holographic grating has a line density of 330 lines per millimeter.

[0074] In the embodiments of this application, such as Figure 10As shown, the red channel imaging system is located after the red channel dispersive grating and includes red channel imaging lenses 20, 21, 22, 23, and 24, and a red channel camera plane window 25. These lenses are sequentially connected along the beam propagation direction. The entrance pupil of the red channel imaging system is located on the diffraction surface of the blue channel dispersive grating.

[0075] In this embodiment, the red channel imaging system is a transmission optical system, employing a similar optical path structure to the blue channel imaging system. All lens materials used have low transmission loss within the operating wavelength band, reducing internal absorption of the optical materials and improving the overall transmittance of the spectrometer.

[0076] In some embodiments, the optical materials of the red channel imaging lens 20, red channel imaging lens 21, red channel imaging lens 22, red channel imaging lens 23, red channel imaging lens 24 and red channel camera plane window 25 are S-FPL53, S-LAH51, PBM2Y, S-LAH58, S-LAL54 and fused silica, respectively.

[0077] In this embodiment, the red channel imaging lens 20 and red channel imaging lens 23 are positive biconvex lenses; the red channel imaging lens 21, red channel imaging lens 22, and red channel imaging lens 24 are meniscus lenses. In some embodiments, the focal length of the red channel imaging system is 98.5 mm. Red channel imaging lens 20 has a focal length of 57.58 mm; red channel imaging lens 21 has a focal length of -88.44 mm; red channel imaging lens 22 has a focal length of -78.72 mm; red channel imaging lens 23 has a focal length of 46.97 mm; and red channel imaging lens 24 has a focal length of -94.64 mm.

[0078] In this embodiment, the red channel camera plane sealing window 25 is the vacuum sealing window glass of the red channel camera, which realizes the vacuum sealing of the detector and deep cooling below -70°C, and reduces the dark current noise of the detector.

[0079] In some embodiments, the focal plane of the red channel detector can be used to mount a deep depletion scientific-grade CCD camera; the quantum effect curve of the deep depletion scientific-grade CCD camera is matched with the operating band of the red channel to achieve high system efficiency at the red end.

[0080] In this embodiment, the focal plane of the red channel detector is tilted at an angle of less than 4 degrees along the spectral direction to compensate for chromatic aberration in the red channel imaging system, reduce the complexity of the red channel imaging optical system, and improve the spectral imaging quality. In some embodiments, the tilt angle of the focal plane of the red channel detector along the spectral direction is 0.975 degrees.

[0081] In some embodiments, a single exposure of the long-slit spectrometer can cover a wide spectral range from 360 nm in the ultraviolet to 985 nm in the near-infrared. The blue channel covers the spectral range from 360 nm to 625 nm, and the red channel covers the spectral range from 600 nm to 985 nm.

[0082] In some implementations, such as Figure 16 As shown, with a slit width of 1.0”, the spectral resolution of the blue channel increases from 566 to 982, and the spectral resolution of the red channel increases from 649 to 1066. The spectral resolution decreases linearly with increasing slit width, and conversely, the spectral resolution increases with decreasing slit width.

[0083] In some embodiments, such as Figure 12 The curve showing the variation of the blue channel RMS speckle radius with wavelength is shown. Figure 14 The blue channel RMS speckle matrix shown has a wavelength range of 360nm to 625nm, an RMS dispersion radius of less than 7.5µm, and the average speckle value clearly shows that the energy is concentrated in a range with a diameter of less than 1.0”.

[0084] In some embodiments, such as Figure 13 The curve showing the variation of the red channel RMS speckle radius with wavelength is shown. Figure 15 The red channel RMS dispersion matrix shown has a red channel range from 600nm to 985nm. The RMS dispersion radius is less than 5µm, and the average dispersion value can also be seen to show that the energy is concentrated in a range with a diameter of less than 1.0”.

Claims

1. A low-resolution dual-channel long-slit spectrometer system for astronomical telescopes, characterized in that, Including those arranged sequentially along the optical path: A slit (1) is set on the focal plane of the telescope to limit the field of view of the incident beam; A field lens (2) is placed in the outgoing light path of the slit (1) to control the exit pupil position of the subsequent optical system; The dichroic cemented prism module is set on the outgoing light path of the field lens (2) to split the incident beam into a blue channel beam and a red channel beam, and the blue channel beam and the red channel beam are emitted in different directions respectively. A blue channel collimating optical system is disposed on the blue channel output light path of the dichroic cemented prism module, and is used to convert the blue channel beam into a collimated beam; A blue channel dispersion grating (7) is disposed on the outgoing optical path of the blue channel collimating optical system and located at its exit pupil position, for dispersing the blue channel collimated beam; The blue channel imaging optical system is set in the outgoing light path of the blue channel dispersive grating (7) and is used to image the dispersive blue channel beam onto the blue channel focal plane (14). A red channel collimating optical system is disposed on the red channel output light path of the dichroic cemented prism module to convert the red channel beam into a collimated beam. The red channel dispersion grating (19) is disposed on the outgoing light path of the red channel collimating optical system and located at its exit pupil position, for dispersing the red channel collimated beam; as well as The red channel imaging optical system is set in the outgoing light path of the red channel dispersive grating (19) and is used to image the dispersed red channel beam onto the red channel focal plane (26). The blue channel focal plane (14) and the red channel focal plane (26) are respectively tilted along the spectral dispersion direction of their respective channels to compensate for the residual chromatic aberration of the corresponding imaging optical system.

2. The low-resolution dual-channel long-slit spectrometer system for astronomical telescopes according to claim 1, characterized in that, The color-separating adhesive prism module includes a parallelogram prism (3) and a refracting optical path prism (15), and the adhesive surfaces of the parallelogram prism (3) and the refracting optical path prism (15) are coated with a color-separating film. The blue channel beam is reflected at the glued surface and exits from the parallelogram prism (3), while the red channel beam is transmitted through the glued surface and exits from the refracting prism (15). The parallelogram prism (3) is used to make the blue channel beam exit direction parallel to the incident beam direction, and the refracting prism (15) is used to make the red channel beam exit direction parallel to the incident beam direction.

3. The low-resolution dual-channel long-slit spectrometer system for astronomical telescopes according to claim 2, characterized in that, The field lens (2) is a plano-convex positive lens, and the field lens (2) is closely bonded to the dichroic cemented prism module.

4. The low-resolution dual-channel long-slit spectrometer system for astronomical telescopes according to claim 1, characterized in that, The blue channel collimating optical system includes a first blue channel collimating lens (4), a second blue channel collimating lens (5), and a third blue channel collimating lens (6) arranged sequentially along the optical path; the first blue channel collimating lens (4) and the second blue channel collimating lens (5) are negative meniscus lenses, and the third blue channel collimating lens (6) is a biconvex positive lens; The red channel collimating optical system includes a first red channel collimating lens (16), a second red channel collimating lens (17), and a third red channel collimating lens (18) arranged sequentially along the optical path; the first red channel collimating lens (16) and the second red channel collimating lens (17) are negative meniscus lenses, and the third red channel collimating lens (18) is a biconvex positive lens.

5. The low-resolution dual-channel long-slit spectrometer system for astronomical telescopes according to claim 1, characterized in that, The blue channel dispersion grating (7) is composed of two prisms and a volume phase holographic grating sandwiched between them. The apex angle of the prism is matched with the center wavelength of the blue channel, so that the blue channel dispersion grating (7) operates at the Littoral incident angle. The red channel dispersion grating (19) is composed of two prisms and a volume phase holographic grating sandwiched between them. The apex angle of the prism is matched with the center wavelength of the red channel, so that the red channel dispersion grating (19) operates at the Littoral incident angle.

6. The low-resolution dual-channel long-slit spectrometer system for astronomical telescopes according to claim 1, characterized in that, The blue channel imaging optical system includes a first blue channel imaging lens (8), a second blue channel imaging lens (9), a third blue channel imaging lens (10), a fourth blue channel imaging lens (11), a fifth blue channel imaging lens (12), and a blue channel camera vacuum sealing glass (13) arranged sequentially along the optical path; the first blue channel imaging lens (8) and the fourth blue channel imaging lens (11) are biconvex positive lenses, and the second blue channel imaging lens (9), the third blue channel imaging lens (10), and the fifth blue channel imaging lens (12) are meniscus lenses; The red channel imaging optical system includes a first red channel imaging lens (20), a second red channel imaging lens (21), a third red channel imaging lens (22), a fourth red channel imaging lens (23), a fifth red channel imaging lens (24), and a red channel camera vacuum sealing glass (25) arranged sequentially along the optical path; the first red channel imaging lens (20) and the fourth red channel imaging lens (23) are biconvex positive lenses, and the second red channel imaging lens (21), the third red channel imaging lens (22), and the fourth red channel imaging lens (24) are meniscus lenses.

7. The low-resolution dual-channel long-slit spectrometer system for astronomical telescopes according to claim 1, characterized in that, The tilt angle of the blue channel focal plane (14) relative to the optical axis of the blue channel imaging optical system is less than 4°, and the tilt angle of the red channel focal plane (26) relative to the optical axis of the red channel imaging optical system is less than 4°.

8. The low-resolution dual-channel long-slit spectrometer system for astronomical telescopes according to claim 1, characterized in that, The blue channel operates in the wavelength range of 360nm to 625nm, and the red channel operates in the wavelength range of 600nm to 985nm. The blue channel and the red channel form a spectral connection in the wavelength range of 600nm to 625nm.

9. The low-resolution dual-channel long-slit spectrometer system for astronomical telescopes according to claim 1, characterized in that, The focal ratios of both the blue channel collimating optical system and the red channel collimating optical system are the same as the incident focal ratio of the telescope, and the incident focal ratio F# is 4 to 12.

10. The low-resolution dual-channel long-slit spectrometer system for astronomical telescopes according to claim 1, characterized in that, The blue channel focal plane (14) is equipped with a scientific-grade CCD camera, and the quantum efficiency curve of the scientific-grade CCD camera matches the working band of the blue channel; the red channel focal plane (26) is equipped with a deep-depletion scientific-grade CCD camera, and the quantum efficiency curve of the deep-depletion scientific-grade CCD camera matches the working band of the red channel.

11. The low-resolution dual-channel long-slit spectrometer system for astronomical telescopes according to claim 1, characterized in that, The exit pupil of the blue channel collimating optical system is located behind its last lens, and the exit pupil of the red channel collimating optical system is located behind its last lens. The blue channel dispersion grating (7) and the red channel dispersion grating (19) are respectively installed at the exit pupil positions of their respective collimating optical systems.

12. The low-resolution dual-channel long-slit spectrometer system for astronomical telescopes according to claim 1, characterized in that, The entrance pupils of the blue channel imaging optical system and the red channel imaging optical system are located on the diffraction surfaces of the blue channel dispersion grating (7) and the red channel dispersion grating (19), respectively.

13. The low-resolution dual-channel long-slit spectrometer system for astronomical telescopes according to claim 1, characterized in that, The vacuum sealing glass (13) of the blue channel camera and the vacuum sealing glass (25) of the red channel camera are used for vacuum sealing of the corresponding detectors to achieve deep cooling with a cooling temperature below -70℃.

14. A terminal spectroscopic observation device for an astronomical telescope, characterized in that, The system includes a telescope and a low-resolution dual-channel long-slit spectrometer system as described in any one of claims 1 to 13, wherein the slit (1) of the low-resolution dual-channel long-slit spectrometer system is located at the focal point or focal point of the telescope.

15. A low-resolution, wide-band, long-slit spectral imaging method for astronomical spectroscopic observations, characterized in that, The low-resolution dual-channel slit spectrometer system according to any one of claims 1 to 13 includes the following steps: Step 1: The incident beam from the telescope is limited to the field of view by the slit (1) and then enters the field lens (2). Step 2: The beam emitted from the field lens (2) enters the dichroic cemented prism module, where the incident beam is split into a blue channel beam and a red channel beam at the cemented surface. The blue channel beam is reflected and then emitted from the dichroic cemented prism module, while the red channel beam is transmitted and then emitted from the dichroic cemented prism module. Step 3: The blue channel beam is collimated by the blue channel collimating optical system, dispersed by the blue channel dispersive grating (7), and imaged by the blue channel imaging optical system, and then focused on the blue channel focal plane (14); at the same time, the red channel beam is collimated by the red channel collimating optical system, dispersed by the red channel dispersive grating (19), and imaged by the red channel imaging optical system, and then focused on the red channel focal plane (26). Step 4: Collect blue channel spectral data and red channel spectral data respectively through detectors set at the blue channel focal plane (14) and the red channel focal plane (26), and stitch the two channel data together to obtain complete spectral data covering a wide band of 360nm to 985nm under a single exposure.

Images