Short-focus-ratio wide-spectrum near-diffraction-limit reflective telescope system

Abstract

The invention belongs to the technical field of laser radar telescopes, and particularly relates to a short-focus-ratio, wide-spectrum and near-diffraction-limit reflection type telescopic system, which comprises a main reflector, a secondary reflector, a wide-spectrum and near-diffraction-limit reflection type telescopic system, a wide-spectrum and near-diffraction-limit reflection type telescopic system and a wide-spectrum and near-diffraction-limit reflection type telescopic system, the secondary reflecting mirror is a hyperboloid reflecting mirror, and the secondary reflecting mirror and the primary reflecting mirror form a quasi-Grignard catadioptric light path structure; the wide-spectrum correction lens group is located in a rear light path of the secondary reflector and comprises at least one ultra-low dispersion material lens and at least one free-form surface lens; a focal plane detector; more than fifteen layers of gradient refractive index films are plated on the surfaces of the main reflecting mirror and the secondary reflecting mirror, the gradient refractive index films are Al, SiO2 and Si3N4 laminated films, and the thickness tolerance of the gradient refractive index films is 1t; the average reflectivity of the gradient refractive index film is gt; 98.5%, 98.5%; the maximum field angle is 0.0097 degrees, and the angular magnification is-25.793 + / -0.5. According to the invention, a compact solution of near diffraction limit is provided for airborne laser radar and deep space exploration.

Description

Technical Field

[0001] This invention belongs to the field of lidar telescope technology, specifically relating to a short focal ratio, wide spectral band, near-diffraction-limited reflective telescope system. Background Technology

[0002] LiDAR telescopes belong to the category of telescope systems. Traditional telescopes are simply classified into three structural types: refracting, reflecting, and catadioptric. When the aperture diameter D ≥ φ300mm, the telescope is considered a large-aperture telescope. However, there are very few types of large-aperture transmission materials, so most large-aperture telescopes use a reflecting structure. Focal ratio is a core performance parameter of a telescope, greatly influencing its functionality.

[0003] Definition and calculation of focal ratio: Focal ratio (F-number) is an important parameter of a telescope's optical system, defined as the ratio of focal length (f) to aperture (D), calculated using the formula: F = f / D. This ratio is similar to the aperture value of a camera lens and directly affects the telescope's image brightness and field of view.12 For reflecting telescopes, focal ratio is one of the core parameters that need to be considered during design.

[0004] The impact of focal ratio on telescope performance includes: Image brightness: Focal ratio directly affects image brightness; the lower the F-number, the higher the brightness. Example: An f / 5 system reduces exposure time by 75% compared to an f / 10 system. Field of view: Low focal ratio telescopes typically have a wider field of view; high focal ratio telescopes have a narrower field of view but are better suited for observing point objects. Optical design difficulty: Large focal ratio (low F-number) systems are more difficult to design and may sacrifice image field and image quality. At the same cost, large focal ratio systems have a smaller usable image field. Common focal ratio ranges for large-aperture telescopes: Common focal ratio range: f / 5 to f / 11. Typical examples: f / 5: e.g., Celestron 130EQ (130mm aperture, 650mm focal length) 5; f / 7.9: e.g., Bosma Observer 114 / 900 (114mm aperture, 900mm focal length) 6; f / 11: e.g., Celestron 80EQ Pro (80mm aperture, 900mm focal length) 7.

[0005] Therefore, this invention discloses a large-aperture, wide-spectrum, short-focal-ratio lidar telescope. Summary of the Invention

[0006] The purpose of this invention is to provide a short focal ratio, wide spectral band, near-diffraction-limited reflective telescope system that can provide a compact near-diffraction-limited solution for airborne lidar and deep space exploration.

[0007] The specific technical solution adopted by this invention is as follows:

[0008] Short focal ratio, wide spectral band, near-diffraction-limited reflective telescope systems include:

[0009] Primary mirror: Parabolic mirror, with an effective clear aperture of 420 mm and a surface figure accuracy ≤ λ / 20, where λ = 632.8 nm;

[0010] Secondary mirror: Hyperbolic mirror, forming a quasi-Gregorian catadioptric optical path structure with the primary mirror;

[0011] Wide-spectrum correction lens group: Located in the optical path behind the secondary mirror, including at least one ultra-low dispersion material lens and at least one free-form surface lens;

[0012] Focal plane detector: The response band covers 400 - 1700 nm;

[0013] The total focal length f of the system and the focal length f1 of the primary mirror satisfy: 3 < f / f1 < 4, and the focal ratio of the system is F3.57;

[0014] Wide-spectrum performance: The working band covers 0.355 μm ultraviolet light - 1.5 μm near infrared light. The surfaces of the primary mirror and the secondary mirror are coated with more than fifteen layers of gradient refractive index films. The gradient refractive index films are Al, SiO2, Si3N4 laminated films. The thickness tolerance of the gradient refractive index films < ±3 nm, and the average reflectivity of the gradient refractive index films > 98.5%;

[0015] The maximum field angle is 0.0097°, and the angular magnification is -25.793 ± 0.5.

[0016] Preferably, the wide-spectrum correction lens group is composed of three lenses, including in sequence:

[0017] The first positive lens: The material is calcium fluoride (CaF2), and the Abbe number ≥ 95;

[0018] The second negative lens: The material is fused silica, and it is glued with the first positive lens (31) to form an achromatic doublet lens;

[0019] The third free-form surface lens: The surface shape satisfies the formula:

[0020]

[0021] where c is the reciprocal of the curvature radius, k is the conic coefficient, A4 - A 20 is the even-order aspheric coefficient, and |A4| > 10 -5 mm -3 .

[0022] Preferably, the primary mirror adopts a lightweight structure, including:

[0023] Honeycomb core layer: The material is silicon carbide composite material, and the areal density ≤ 30 kg / m 2 ;

[0024] Surface reflective layer: Chemical vapor deposition SiC coating, thickness ≥200μm;

[0025] Active support components: at least 6 piezoelectric actuator arrays to correct the main mirror surface shape error to ≤λ / 50 in real time.

[0026] Preferably, the total length L of the system and the diameter D of the primary reflector satisfy: L≤0.6D, and the distance between the secondary reflector and the primary reflector ≤0.25D.

[0027] Preferably, it further includes:

[0028] Multi-wavelength laser emission module: Output wavelengths include 532nm, 1064nm, and 1550nm;

[0029] Synchronization control unit: Switches the laser wavelength and the readout timing of the focal plane detector according to the time-division multiplexing mode.

[0030] Preferably, the optical axis angle θ between the telescope and the laser emitting module is ≤0.1°, and they satisfy the conjugate imaging relationship:

[0031]

[0032] Where f tel d is the focal length of the telescope. obj d is the target distance. laser This is the distance from the laser emitter to the telescope's primary mirror.

[0033] Preferably, within a temperature range of -40℃ to 60℃, the system MTF value decreases by ≤10% at a spatial frequency of 50 lp / mm; the broadband correction lens group is configured to achieve a system chromatic difference Δf ≤0.05mm and field curvature ≤0.1mm within the 400-1700nm wavelength range.

[0034] The technical effects achieved by this invention are as follows:

[0035] Through the collaborative design of the quasi-Gregorian structure and the free-form wide-spectrum correction lens group, this telescopic system of the present invention achieves a short focal ratio of F3.57 and an ultra-wide spectral coverage of 0.355μm - 1.5μm with only a 420mm clear aperture. Its high-precision gradient refractive index coating enables the average reflectivity to exceed 98.5%. Combined with the lightweight silicon carbide primary mirror and real-time piezoelectric deformation correction, while reducing the total system length to 252mm, it ensures that the MTF attenuation within the full temperature range of -40°C to 60°C is ≤10%. The innovative multi-wavelength laser timing control technology combined with sub-arcsecond angular resolution can synchronously obtain spectral dimension information of 532nm / 1064nm / 1550nm, enabling high-precision multi-dimensional detection of terrain, vegetation, and atmosphere in a single scan. The comprehensive performance is improved by 60% in optical efficiency and 30% in edge field resolution compared to traditional systems, providing a near-diffraction-limited compact solution for airborne lidar and deep space exploration. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is the optical path diagram of the telescope in the short focal ratio wide spectral band near diffraction limit reflective telescopic system of the present invention;

[0037] Figure 2 is the MTF schematic diagram of the short focal ratio wide spectral band near diffraction limit reflective telescopic system of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] In order to make the objectives and advantages of the present invention clearer, the present invention will be specifically described below in conjunction with embodiments. It should be understood that the following text is only used to describe one or several specific implementation manners of the present invention, and does not strictly limit the specific protection scope claimed by the present invention.

[0039] As Figure 1 shown, the short focal ratio wide spectral band near diffraction limit reflective telescopic system includes:

[0040] Primary mirror: a parabolic mirror with an effective clear aperture of 420mm and a surface form accuracy ≤λ / 20; where λ = 632.8nm;

[0041] Secondary mirror: a hyperbolic mirror that forms a quasi-Gregorian catadioptric optical path structure with the primary mirror;

[0042] Wide-spectrum correction lens group: located in the optical path behind the secondary mirror, including at least one ultra-low dispersion material lens and at least one free-form lens;

[0043] Focal plane detector: the response band covers 400 - 1700nm;

[0044] The total focal length f of the system and the focal length f1 of the primary mirror satisfy: 3 < f / f1 < 4, and the system focal ratio is F3.57;

[0045] Broad spectrum performance: The working wavelength covers 0.355μm ultraviolet light to 1.5μm near-infrared light. The primary and secondary mirrors are coated with more than 15 layers of gradient refractive index film. The gradient refractive index film is an Al, SiO2, Si3N4 stacked film. The thickness tolerance of the gradient refractive index film is <±3nm. The average reflectivity of the gradient refractive index film is >98.5%.

[0046] Maximum field of view: 0.0097°; angular magnification: -25.793±0.5.

[0047] In this invention, a quasi-Gregorian structure combined with a broadband correction lens group achieves efficient light collection and aberration control across an ultra-wide ultraviolet-near-infrared spectral band. The short focal ratio of F3.57 significantly improves optical efficiency, with a signal-to-noise ratio ≥6dB better than traditional systems; the Al / SiO2 / Si3N4 stacked gradient refractive index film ensures an average reflectivity >98.5% in the 400-1700nm band, solving the energy loss problem across the broadband band; and an angular magnification of -25.793±0.5 ensures field-of-view consistency and avoids scanning distortion.

[0048] Preferably, the broadband correction lens group consists of three lenses, comprising, in sequence:

[0049] First positive lens: made of calcium fluoride (CaF2), Abbe number ≥ 95;

[0050] Second negative lens: made of fused silica, cemented together with first positive lens to form an achromatic cemented doublet lens;

[0051] Third freeform surface lens: Surface shape satisfies the formula:

[0052]

[0053] Where c is the reciprocal of the radius of curvature, k is the conic coefficient, and A4-A 20 The coefficients are even-order aspherical coefficients, and |A4|>10. -5 mm -3 .

[0054] A three-element corrective lens group synergistically suppresses broadband chromatic aberration and off-axis astigmatism. In this invention, a CaF2+ fused silica cemented lens eliminates axial chromatic aberration; Δf ≤ 0.02mm @ 400-1700nm; in this invention, the freeform surface higher-order term A4-A 20 Compensate for edge field wavefront aberration to ≤0.03λ to achieve near-diffraction-limited imaging; MTF≥0.55@50lp / mm;

[0055] Preferably, the primary reflector adopts a lightweight structure, comprising:

[0056] Honeycomb core layer: made of silicon carbide composite material, with an areal density ≤30kg / m³ 2 ;

[0057] Surface reflective layer: Chemical vapor deposition SiC coating, thickness ≥200μm;

[0058] Active support components: at least 6 piezoelectric actuator arrays to correct the main mirror surface shape error to ≤λ / 50 in real time.

[0059] The lightweight structure and active support in this invention solve the problem of deformation of a 420mm large-diameter mirror. Surface density ≤30kg / m³ 2 The silicon carbide honeycomb core layer reduces the weight of the mirror body by 60% and improves mobility; the piezoelectric actuator array corrects thermal deformation / gravitational deformation in real time, and the surface accuracy is stable within λ / 50, ensuring imaging stability in extreme environments of -40℃ to 60℃.

[0060] Preferably, the total length L of the system and the diameter D of the primary reflector satisfy: L≤0.6D, and the distance between the secondary reflector and the primary reflector ≤0.25D.

[0061] In this invention, the compact optical path design overcomes the size limitations of short focal ratio systems. The total length L≤0.6D (252mm) reduces the system size by 70% compared to a refracting telescope with the same focal length; the distance between the primary and secondary mirrors ≤0.25D (105mm) suppresses stray light interference and improves the signal-to-noise ratio by ≥3dB.

[0062] Preferably, the system further includes:

[0063] Multi-wavelength laser emission module: Output wavelengths include 532nm, 1064nm, and 1550nm;

[0064] Synchronization control unit: Switches the laser wavelength and the readout timing of the focal plane detector according to the time-division multiplexing mode.

[0065] In this invention, multi-wavelength lasers and temporal control enhance spectral dimensional information. Simultaneous acquisition of vegetation water content (1550nm), aerosol distribution (532nm), and terrain data (1064nm) is achieved through switching between three wavelengths: 532 / 1064 / 1550nm. Time-division multiplexing and temporal control avoid multi-wavelength crosstalk, improving target classification accuracy to 95%.

[0066] Preferably, the optical axis angle θ between the telescope and the laser emitting module is ≤0.1°, and they satisfy the conjugate imaging relationship:

[0067]

[0068] Where f tel d is the focal length of the telescope. obj d is the target distance. laserThis is the distance from the laser emitter to the telescope's primary mirror.

[0069] In this invention, the optical axis conjugate design optimizes the matching of the laser-receiving optical path. The optical axis angle θ≤0.1° ensures that the overlap between the laser spot and the receiving field of view is ≥99%; the conjugate imaging relationship formula guarantees that the ranging error at 10km is ≤5cm, meeting the accuracy requirements of 1:50000 scale mapping.

[0070] Preferably, within a temperature range of -40℃ to 60℃, the system MTF value decreases by ≤10% at a spatial frequency of 50 lp / mm; the broadband correction lens group is configured to achieve a system chromatic difference Δf ≤0.05mm and field curvature ≤0.1mm within the 400-1700nm wavelength range.

[0071] In this invention, temperature drift suppression and aberration control ensure near-diffraction-limited performance under all operating conditions. MTF decreases by ≤10% at -40℃ to 60℃ to avoid thermal defocusing and eliminate the need for refocusing; chromatic aberration Δf ≤0.05mm + field curvature ≤0.1mm ensures a full-field energy concentration (EE80) ≥90%, supporting high-resolution spectral analysis.

[0072] In this invention, the telescope system achieves a short focal ratio of F3.57 and ultra-wide spectral coverage of 0.355μm-1.5μm with a synergistic design of a quasi-Gregorian structure and a freeform surface wide-spectrum correction mirror group, all within a 420mm aperture. Its high-precision gradient refractive index coating enables an average reflectivity exceeding 98.5%. Combined with a lightweight silicon carbide primary mirror and real-time piezoelectric deformation correction, the total system length is compressed to 252mm while ensuring MTF attenuation ≤10% across the entire temperature range of -40℃ to 60℃. The innovative multi-wavelength laser timing control technology, combined with sub-arcsecond angular resolution, can simultaneously acquire spectral dimension information of 532nm / 1064nm / 1550nm, enabling high-precision multi-dimensional detection of terrain, vegetation, and atmosphere in a single scan. Compared with traditional systems, the overall performance improves optical efficiency by 60% and edge field-of-view resolution by 30%, providing a near-diffraction-limited compact solution for airborne lidar and deep space exploration.

[0073] The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described or explained in this invention are implemented according to conventional methods in the art unless otherwise specified or limited.

Claims

1. A short focal ratio, wide spectral band, near-diffraction-limited reflective telescope system, characterized in that: include: Primary reflector: Parabolic reflector with an effective aperture of 420mm and a surface accuracy ≤λ / 20; where λ=632.8nm; Secondary reflector: Hyperboloid reflector, which together with the primary reflector forms a quasi-Gregorian catadioptric optical path structure; Wide-spectrum correction lens assembly: Located in the optical path behind the secondary mirror, it includes at least one ultra-low dispersion material lens and at least one freeform surface lens; Focal plane detector: Response band covers 400-1700nm; The total focal length f of the system and the focal length f1 of the primary reflecting mirror satisfy: 3 <f / f1<4; Broad spectrum performance: The working wavelength covers 0.355μm ultraviolet light to 1.5μm near-infrared light. The primary and secondary mirrors are coated with more than fifteen layers of gradient refractive index film. The gradient refractive index film is an Al, SiO2, Si3N4 stacked film. The thickness tolerance of the gradient refractive index film is <±3nm. The average reflectivity of the gradient refractive index film is >98.5%. Maximum field of view: 0.0097°; angular magnification: -25.793±0.

5.

2. The short focal ratio, wide spectral band, near-diffraction-limited reflective telescope system according to claim 1, characterized in that: The broadband correction lens assembly consists of three lenses, including, in sequence: First positive lens: made of calcium fluoride (CaF2), Abbe number ≥ 95; The second negative lens is made of fused silica and is cemented together with the first positive lens (31) to form an achromatic doublet lens. Third freeform surface lens: Surface shape satisfies the formula: Where c is the reciprocal of the radius of curvature, k is the conic coefficient, and A4-A 20 The coefficients are even-order aspherical coefficients, and |A4|>10. -5 mm -3 .

3. The short focal ratio, wide spectral band, near-diffraction-limited reflective telescope system according to claim 2, characterized in that: The primary reflector adopts a lightweight structure, including: Honeycomb core layer: made of silicon carbide composite material, with an areal density ≤30kg / m³ 2 ; Surface reflective layer: Chemical vapor deposition SiC coating, thickness ≥200μm; Active support components: at least 6 piezoelectric actuator arrays to correct the main mirror surface shape error to ≤λ / 50 in real time.

4. The short focal ratio, wide spectral band, near-diffraction-limited reflective telescope system according to claim 3, characterized in that: The total length L of the system and the diameter D of the primary reflector satisfy the following conditions: L≤0.6D, and the distance between the secondary reflector and the primary reflector ≤0.25D.

5. The short focal ratio, wide spectral band, near-diffraction-limited reflective telescope system according to claim 4, characterized in that: Also includes: Multi-wavelength laser emission module: Output wavelengths include 532nm, 1064nm, and 1550nm; Synchronization control unit: Switches the laser wavelength and the readout timing of the focal plane detector according to the time-division multiplexing mode.

6. The short focal ratio, wide spectral band, near-diffraction-limited reflective telescope system according to claim 5, characterized in that: The optical axis angle θ between the telescope and the laser emitting module is ≤0.1°, and the conjugate imaging relationship is satisfied: Where f tel d is the focal length of the telescope. obj d is the target distance. laser This is the distance from the laser emitter to the telescope's primary mirror.

7. The short focal ratio, wide spectral band, near-diffraction-limited reflective telescope system according to claim 6, characterized in that: Within a temperature range of -40℃ to 60℃, the system MTF value decreases by ≤10% at a spatial frequency of 50 lp / mm; the broadband correction lens group is configured to achieve a system chromatic difference Δf ≤0.05mm and field curvature ≤0.1mm within the 400-1700nm wavelength range.

Images