Energy detection optical system based on multi-stage suppression of pupil relay and stray light and space laser detection device thereof

Abstract

An energy detection optical system based on pupil relay and multi-stage stray light suppression design, which comprises Cassegrain telescope, pre-filter, field stop, relay lens group, narrow-band filter and detector in sequence along the optical path. The core of the present application is the synergistic architecture relationship between the relay lens group and the field stop and the narrow-band filter: the relay lens group is configured to simultaneously and co-optically realize triple function coupling, that is, ① imaging the system entrance pupil on the detector target surface to realize pupil matching; ② compressing the light beam into collimated light for the narrow-band filter to work; ③ transmitting the light beam energy filtered by the field stop to the detector target surface. This synergistic architecture, combined with the pre-filter and the post-narrow-band filter, constitutes a multi-stage stray light suppression system from wide to narrow, so that the system point source transmission ratio (PST) is better than 10 ‑9 , has the ability to detect photon level signals, and has compact structure and wide tolerance.

Description

Technical Field

[0001] This invention relates to the field of space optical detection technology, and in particular to an energy detection optical system and its space laser detection device based on pupil relay and stray light multi-level suppression design. Background Technology

[0002] In cutting-edge fields such as astronomical observation, space environment monitoring, and quantum communication, extreme demands are placed on the signal-to-noise ratio of optical systems, requiring them to be able to detect signals at the photon level. One of the key factors limiting detection sensitivity is the level of stray light in the system.

[0003] Traditional space optical system designs typically optimize image quality first, then suppress stray light through methods such as adding light-blocking rings and surface treatments. This approach has the following limitations: 1. Passive suppression: Stray light suppression measures are added after the optical design is finalized, and their effect is limited, making it difficult to achieve extremely low stray light levels (e.g., point source transmittance PST < 10). -9 ).

[0004] 2. System complexity: Additional light-shielding structures increase the size, weight and complexity of the system, which is not conducive to miniaturization and lightweight design.

[0005] 3. Performance bottleneck: When a narrowband filter operates under a non-parallel beam, its passband characteristics will shift and deteriorate, reducing the filtering efficiency and directly affecting the signal-to-noise ratio of the system.

[0006] 4. Difficult assembly and adjustment: The complex mechanical structure and post-installed suppression measures place higher demands on the system's assembly, adjustment, and tolerance, affecting engineering feasibility and long-term on-orbit stability.

[0007] Therefore, there is an urgent need for an integrated optical system configuration that takes stray light suppression as a core design principle from the initial stage of optical design. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of existing technologies and provide an energy detection optical system and its space laser detection device based on pupil relay and stray light multi-level suppression design. This system deeply integrates the stray light suppression concept into the optical configuration design, featuring a compact configuration, relaxed tolerance, easy assembly and adjustment, and good on-orbit stability. It can achieve extremely low stray light levels and extremely high detection signal-to-noise ratio, meeting the detection requirements of photon-level signals.

[0009] The technical solution of the present invention is as follows: An energy detection optical system based on pupil relay and stray light multi-level suppression design is characterized by comprising the following components arranged sequentially along the optical axis: A reflective telescope imaging component is used to collect incident light rays and converge them to form an intermediate image plane; A pre-filter is disposed in the converging optical path between the reflective telescope imaging component and the intermediate image plane; A field stop is positioned at the intermediate image plane, and its aperture defines the instantaneous field of view of the system. The relay lens group has its object-side field of view covering the aperture of the field stop; Narrowband filters, and The detector has a photosensitive target surface; The optical structure of the relay lens group is configured to image the entrance pupil of the reflective telescope imaging component onto the photosensitive target surface of the detector, so that the photosensitive target surface simultaneously serves as the exit pupil surface and signal receiving surface of the system; and to shape the beam passing through the field stop into a collimated beam or a low divergence angle beam; and to transmit the energy of the beam in the field of view after being filtered by the field stop to the detector target surface. The narrowband filter is disposed in the path of the collimated beam or low divergence angle beam inside the relay lens group; the pre-filter and the narrowband filter form a series spectral filtering chain, wherein the passband bandwidth of the pre-filter is greater than the passband bandwidth of the narrowband filter.

[0010] Furthermore, the reflective telescope imaging component is a Cassegrain telescope structure, including a primary mirror and a secondary mirror arranged coaxially; the primary mirror is a concave reflector, and the secondary mirror is a convex reflector, with light reflected by the primary mirror to the secondary mirror and then reflected to the intermediate image plane.

[0011] Furthermore, the center wavelength of the pre-filter coincides with the center wavelength of the narrowband filter, the full width at half maximum (FWHM) bandwidth of the pre-filter is 10 nm to 40 nm, and the full WHM bandwidth of the narrowband filter is 0.5 nm to 5 nm.

[0012] Furthermore, it also includes an aperture stop; the aperture stop is disposed between the relay lens group and the detector, or integrated into the edge of the photosensitive target surface of the detector; the aperture size of the aperture stop is less than or equal to the size of the entrance pupil image formed by the relay lens group on the photosensitive target surface, and is used to block stray light formed by the scattering of light from the edge field of view.

[0013] Furthermore, the relay lens group converts the first F-number beam output by the reflective telescope imaging component into a second F-number beam; wherein the first F-number ranges from F / 4 to F / 5, and the second F-number ranges from F / 4 to F / 20, to ensure that the light passes through the narrowband filter at an angle close to normal incidence.

[0014] Furthermore, the system is configured such that the target signal within the field of view converges on the photosensitive target surface, while stray light entering the system from outside the field of view is blocked outside the aperture stop; on the photosensitive target surface, the energy density of stray light from outside the field of view per unit area is less than one billionth of the energy density of the target signal within the field of view.

[0015] Furthermore, the system exhibits a point source transmittance (PST) better than 10 at large off-axis angles θ. -9 .

[0016] Furthermore, the large off-axis angle θ is 50°~80°.

[0017] Second, the present invention also provides a space laser detection device, characterized in that it includes an energy detection optical system based on pupil relay and multi-level stray light suppression as described in any one of claims 1 to 9, and a signal processing circuit; the signal processing circuit is electrically connected to the output terminal of the detector and is used to process the photoelectric signal output by the detector.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. System-level integrated suppression design: Taking stray light suppression as the core design metric, a highly efficient stray light suppression system is constructed in principle through a dual mechanism of "field stop spatial filtering" and "entry pupil relay imaging filtering," achieving a performance of PST<10. -9 This laid the foundation for photon-level detection.

[0019] 2. Extremely high system detection signal-to-noise ratio: The optimized beam shaping by the relay mirror group ensures the performance limit of the narrowband filter, greatly suppresses background noise, and significantly improves the signal-to-noise ratio of the entire receiving system.

[0020] 3. Compact and efficient receiving system configuration: All functions are achieved through the optical design itself, resulting in a compact structure that avoids complex external light-shielding devices, making it particularly suitable for space applications.

[0021] 4. Excellent engineering feasibility and stability: The Cassegrain configuration itself and the coordination of its relay mirrors make the system have a loose tolerance, simple assembly, adjustment and testing, high reliability, and ensure the performance stability of long-term on-orbit operation.

[0022] 5. Synergistic effect of spectral suppression: By setting a pre-filter with a bandwidth of 20nm, in synergy with a narrower band filter, a two-stage spectral screening from wide to narrow is achieved. The pre-filter filters out most of the out-of-band radiation in advance, reducing the thermal load and drift risk of the narrowband filter, and ensuring the long-term stability and ultimate performance of its core filtering performance. This is a key design for achieving an extremely high signal-to-noise ratio. Attached Figure Description

[0023] Figure 1This is a schematic diagram of the overall optical path structure of the energy detection optical system based on pupil relay and multi-level stray light suppression of the present invention.

[0024] Figure 2 This is a schematic diagram illustrating the beam angle compression and narrowband filter operation of the relay imaging lens assembly.

[0025] Figure 3 To illustrate the entrance pupil imaging onto the detector target surface, the outer circles of the light trails representing each field of view all coincide within a circular region with a diameter of 5.24 mm.

[0026] The numbers in the diagram are: 1-primary mirror; 2-secondary mirror; 3-pre-filter; 4-intermediate image plane / field stop; 5-narrowband filter; 6-relay mirror group; 7-detector target surface. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0028] like Figure 1 As shown, this embodiment provides an energy detection optical system based on pupil relay and multi-level stray light suppression, which includes, along the optical axis, a Cassegrain telescope module consisting of a primary mirror 1 and a secondary mirror 2, a pre-filter 3, a field stop 4, a relay mirror group 6, a narrowband filter 5, and a detector 7.

[0029] In this embodiment, the Cassegrain telescope module serves as the front-end receiving unit of the system, responsible for collecting weak light signals and performing the first imaging. The primary mirror 1 is a concave reflector, and the secondary mirror 2 is a convex reflector, both coaxially arranged. Light rays are reflected from the primary mirror 1 to the secondary mirror 2, and then reflected again by the secondary mirror 2, converging at the field stop 4, effectively blocking light rays outside the field of view. This embodiment preferably employs a Cassegrain structure to eliminate spherical aberration and coma, ensuring imaging quality over a large field of view.

[0030] The pre-filter 3 is positioned before the focal plane of the Cassegrain telescope module, specifically on the converging path of the beam reflected from the secondary mirror 2. Its function is to perform first-stage spectral screening, filtering out most of the background radiation outside the target wavelength band. In this embodiment, for a 532nm laser echo detection application, the center wavelength of the pre-filter 3 is 532nm, and its full width at half maximum (FWHM) bandwidth is 20nm. This pre-filter not only reduces the thermal load on subsequent optical components but also effectively prevents detector saturation or narrowband filter performance drift caused by strong background light.

[0031] Field stop 4 is positioned at the central image plane (focal plane) of the Cassegrain telescope module. The aperture of this field stop is matched to the instantaneous field of view (IFOV) designed for the system. Target signal beams from within the field of view can pass through field stop 4 without loss, while stray light from outside the field of view (such as the Earth's background, direct sunlight, etc.) is directly blocked by the solid portion of field stop 4.

[0032] The input of relay lens group 6 receives the diverging beam from field stop 4. For example... Figure 2 As shown, in this embodiment, the relay lens group 6 consists of four spherical lenses, divided into a front group and a rear group. The front group is used for beam collimation, and the rear group is used for beam convergence. The relay lens group 6, as a single component, is designed to simultaneously perform three core functions: (1) Pupil relay function: The relay lens group 6 clearly images the entrance pupil (i.e. the aperture of the primary mirror 1) of the system onto the target surface of the detector 7, so that the target surface also becomes the exit pupil of the system, realizing pupil matching. (2) Beam compression function: The relay mirror group 6 converts the converging beam with an F number of 4.3 from the Cassegrain telescope module into a collimated beam, providing a beam that meets the working angle requirements of the narrowband filter 5 in the collimated optical path; (3) Energy transmission function: The relay mirror group 6 transmits the energy of the beam in the field of view after being filtered by the field stop 4 to the target surface of the detector 7.

[0033] Narrowband filter 5 is positioned in the optical path of the collimated beam generated by repeater lens group 6, specifically between the front and rear groups of repeater lens group 6. Since the beam is nearly collimated at this location, with an incident angle close to 0 degrees, narrowband filter 5 can operate with its designed center wavelength and extremely narrow bandwidth, avoiding blue shift of the passband and decrease in transmittance caused by large-angle incident light. In this embodiment, the center wavelength of narrowband filter 5 is 532 nm, and its bandwidth is 1.5 nm. Together with pre-filter 3, it forms a two-stage spectral filtering system of "20 nm + 1.5 nm," significantly improving the overall suppression ratio.

[0034] Detector 7 is located at the output end of relay mirror group 6. Its target surface is not only the photoelectric conversion interface, but also the pupil surface of the system. In a preferred embodiment, an aperture stop is also provided in front of the target surface of detector 7. The aperture of the aperture stop is slightly smaller than the size of the entrance pupil image, which is used to further block residual stray light generated by diffraction or scattering from the edge of the optical element, forming the final spatial filtering closed loop.

[0035] Example system design parameters: telescope focal length 1124mm, aperture 260mm, f-number 4.3, field of view 1.2°. The relay mirror group compresses and focuses the beam onto the energy detector (PMT). Simulation results show that the PST is better than 10 at an off-axis angle of 60°. -9It meets the requirements for detecting extremely weak signals in orbit. The system features a modular design, is easy to assemble and adjust, and has high stability.

[0036] The pre-filter 3 has a center wavelength of 532nm and a bandwidth of 20nm, and is used to filter out most of the background light near this wavelength. The narrowband filter 5 has a center wavelength of 532nm and a bandwidth of <5nm. Precise spectral selection is performed based on the pre-filter. The two work together to form a highly efficient spectral suppression chain.

[0037] The workflow and stray light suppression mechanism of this system are as follows: Signal Acquisition and Pre-Filtering: External light signals (including weak target signals and strong background noise) enter the Cassegrain telescope. Pre-filter 3 first filters out most of the broadband background light outside the 532nm band (such as other components in the solar spectrum) to reduce the system's thermal effects.

[0038] Spatial coarse screening: The beam converges at field stop 4. The target signal within the field of view passes smoothly; strong stray light outside the field of view is physically blocked by the stop blades. At this point, most of the off-axis stray light has been eliminated.

[0039] Beam shaping and fine filtering: The beam passing through the field stop enters the repeater group 6. The repeater group collimates the beam, and the narrow-band filter 5 "fine-processes" the spectrum in this collimated optical path, allowing only the target signal within a 1.5nm bandwidth to pass through, further filtering out out-of-band noise and atmospheric scattered light remaining from the pre-filter.

[0040] Pupil matching and final suppression: The spectrally filtered beam converges in the latter half of the relay mirror group and is finally imaged onto detector 7. The key is that the relay mirror group simultaneously images the primary mirror 1 (entry pupil) onto detector 7.

[0041] For signals within the field of view: their energy is concentrated and fills the entrance pupil image, and they are efficiently received by the detector.

[0042] For residual stray light (such as specular scattered light): Due to the pupil relay characteristics, this stray light is outside the detector pupil region. With the help of a possible aperture stop, the energy density of this diffuse stray light is greatly diluted, and the peak power is far below the detection threshold.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art can make various improvements and modifications without departing from the spirit and principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An energy detection optical system based on pupil relay and stray light multi-level suppression design, characterized in that, Including those arranged sequentially along the optical axis: A reflective telescope imaging component is used to collect incident light rays and converge them to form an intermediate image plane; A pre-filter is disposed in the converging optical path between the reflective telescope imaging component and the intermediate image plane; A field stop is positioned at the intermediate image plane, and its aperture defines the instantaneous field of view of the system. The relay lens group has its object-side field of view covering the aperture of the field stop; Narrowband filters, and The detector has a photosensitive target surface; The optical structure of the relay lens group is configured to image the entrance pupil of the reflective telescope imaging component onto the photosensitive target surface of the detector, so that the photosensitive target surface simultaneously serves as the exit pupil surface and signal receiving surface of the system; and to shape the beam passing through the field stop into a collimated beam or a low divergence angle beam; and to transmit the energy of the beam in the field of view after being filtered by the field stop to the detector target surface. The narrowband filter is disposed in the path of the collimated beam or low divergence angle beam inside the relay lens group; the pre-filter and the narrowband filter form a series spectral filtering chain, wherein the passband bandwidth of the pre-filter is greater than the passband bandwidth of the narrowband filter.

2. The energy detection optical system based on pupil relay and stray light multi-level suppression design according to claim 1, characterized in that, The reflective telescope imaging assembly is a Cassegrain telescope structure, including a primary mirror and a secondary mirror arranged coaxially; the primary mirror is a concave reflector, and the secondary mirror is a convex reflector. Light is reflected by the primary mirror to the secondary mirror and then reflected to the intermediate image plane.

3. The energy detection optical system based on pupil relay and stray light multi-level suppression design according to claim 1, characterized in that, The center wavelength of the pre-filter coincides with the center wavelength of the narrowband filter. The full width at half maximum (FWHM) bandwidth of the pre-filter is 10 nm to 40 nm, and the full WHM bandwidth of the narrowband filter is 0.5 nm to 5 nm.

4. The energy detection optical system based on pupil relay and stray light multi-level suppression design according to claim 1, characterized in that, It also includes an aperture stop; the aperture stop is disposed between the relay lens group and the detector, or integrated into the edge of the photosensitive target surface of the detector; the aperture size of the aperture stop is less than or equal to the size of the entrance pupil image formed by the relay lens group on the photosensitive target surface, and is used to block stray light formed by the scattering of light from the edge field of view.

5. The energy detection optical system based on pupil relay and stray light multi-level suppression design according to claim 1, characterized in that, The relay lens group converts the first F-number beam output by the reflective telescope imaging component into a second F-number beam; wherein the first F-number ranges from F / 4 to F / 5, and the second F-number ranges from F / 4 to F / 20, to ensure that the light passes through the narrowband filter at an angle close to normal incidence.

6. The energy detection optical system based on pupil relay and stray light multi-level suppression design according to claim 1, characterized in that, The system is configured such that target signals within the field of view converge on the photosensitive target surface, while stray light entering the system from outside the field of view is blocked outside the aperture stop. On the photosensitive target surface, the energy density of stray light outside the field of view per unit area is less than one billionth of the energy density of the target signal within the field of view.

7. The energy detection optical system based on pupil relay and stray light multi-level suppression design according to claim 1, characterized in that, The system has a point source transmittance (PST) better than 10 at large off-axis angles θ. -9 .

8. The energy detection optical system based on pupil relay and stray light multi-level suppression design according to claim 1, characterized in that, The maximum off-axis angle θ is 50°~80°.

9. A space laser detection device, characterized in that, The system includes an energy detection optical system based on pupil relay and multi-level stray light suppression as described in any one of claims 1 to 9, and a signal processing circuit; the signal processing circuit is electrically connected to the output terminal of the detector and is used to process the photoelectric signal output by the detector.

Images