RU2769088C1 - Catadioptric lens - Google Patents

Abstract

FIELD: optics.SUBSTANCE: invention can be used in space-based telescopes for remote probing of the Earth in the infrared region of the spectrum. Catadioptric lens comprises a mirror lens consisting of a main concave hyperbolic mirror and a convex hyperbolic mirror, a lens projection lens with an optical axis aligned with the optical axis of the mirror lens. In the plane of the intermediate image created by the mirror lens, a collective is installed in the form of a biconcave lens, and in the plane of its image there is an optoelectronic receiver. Lens projection lens is made of two components. Optical power of the lenses satisfies the conditions specified in the claims. Lens is supplemented with a cryostat, and the exit pupil of the lens is aligned with the cryostat window and is located at a distance from the optoelectronic receiver of not more than 0.01÷0.02f'.EFFECT: high resolution by reducing aberrations in the pupils and increasing aperture ratio and angular field.1 cl, 2 dwg

Description

The present invention relates to the field of optical instrumentation, in particular, to space-based mirror-lens telescopes designed for remote sensing of the Earth (ERS) in the infrared (IR) region of the spectrum (3-5 microns, 8-14 microns).

The following basic requirements are imposed on space optical systems operating in the IR region of the spectrum in the range of 3-5 microns or 8-14 microns:

, где Н - высота орбиты.1. Large focal lengths f' (more than 1÷2 m) provide the minimum dimensions of the projection (α') of the optoelectronic receiver (OED) element - α (matrix pixel) on the Earth's surface and, accordingly, the minimum linear resolution is equal to the size of the pixel projection, determined by formula

, where H is the height of the orbit.

, где D - диаметр входного зрачка для получения требуемой освещенности в плоскости оптико-электронных приемников.2. Large bore

, where D is the diameter of the entrance pupil to obtain the required illumination in the plane of optoelectronic receivers.

3. Registered objects are self-emitting radiation sources with spectra determined by Planck's law.

OED registers the radiation of both the object and all possible elements of the lens design that create an unacceptable background. To exclude it, a part of the optical system from the plane of the exit pupil to the optoelectronic receiver is placed in a cryostat.

The cryostat window should strictly match the size of the exit pupil, and to save the energy of the apparatus, the length of the cryostat should be as short as possible, for example, 20–30 mm.

Known mirror-lens lenses for remote sensing of the Earth, consisting of the main concave and second convex mirrors and lens field aberration corrector, installed after the second convex mirror in front of the focal plane of the entire lens [1].

The disadvantage of the known lens is the absence of a valid image of the pupil.

The pupil of the lens - the main mirror has an imaginary position, i.e. located in front of the focal plane near the second convex mirror. In such a system, it is impossible to install the cryostat so that its window coincides with the exit pupil. In this case, the background illumination exceeds the operating signal, and the system becomes inoperable in the IR range.

The closest technical solution to the proposed invention is a mirror-lens lens [2], containing a main concave mirror, a second hyperbolic convex mirror, a lens projection lens with an optical axis aligned with the optical axis of the lens, in the plane of the intermediate image of the lens created by the first and the second mirrors, a collective is installed, and an optoelectronic receiver is installed in the image plane of the lens.

The disadvantage of the mirror-lens lens adopted as a prototype is the limited relative aperture and angular field due to the use of aspherical surfaces of the main and second mirrors: elliptical plus hyperbolic surfaces, respectively, the location of the exit pupil near the projection lens. In addition, there are large aberrations in the pupils. Those. due to aberrations in the pupils, the size of the exit pupil is larger than its size along the aperture beam.

The main problem to be solved by the invention is to increase the resolving power of a mirror-lens objective by reducing aberrations in the pupils and increasing the relative aperture and the angular field.

To solve this problem, a mirror-lens lens is proposed, which, like the prototype, contains a mirror lens consisting of a main concave mirror and a second hyperbolic convex mirror installed in series, a lens projection lens with an optical axis aligned with the optical axis of the mirror lens in the plane of the intermediate image of the object created by the main concave and the second convex mirrors, a collective is installed, and an optoelectronic receiver is installed in the plane of its image.

Unlike the prototype, the main concave mirror of the mirror lens is made hyperbolic, the collective is made in the form of a biconcave lens with an optical power ϕ _to satisfy the condition: 40 < |ϕ _to /ϕ| < 80, where ϕ is the optical power of the entire mirror lens, the lens projection lens is made of two components, the first of which is a positive meniscus, convexly facing the image plane, with an optical power ϕ _I , the second component is made of three lenses, of which the first lens is biconvex with optical power ϕ _II,1 , the second lens is a negative meniscus, convexly facing the image plane, with optical power ϕ _II,2 , the third lens is a positive meniscus, concavity facing the image plane, with optical power ϕ _{II, 3} , while the optical powers of the lenses satisfy the condition:

20 < ϕ _I /ϕ < 40 14 < ϕ _II,1 / ϕ < 22

4 < ϕ _II,2 /ϕ < 8 18 < ϕ _II,3 / ϕ < 30

0.8 < ϕ _I / ϕ _II < 1.2,

in addition, the lens is supplemented with a cryostat, and the exit pupil of the lens is aligned with the cryostat window and located at a distance of no more than 0.01÷0.02f' from the optoelectronic receiver.

The essence of the proposed mirror-lens objective is as follows:

- Implementation of the surface of the main mirror of a hyperbolic shape in conjunction with the hyperbolic shape of the surface of the second convex mirror, i.e. with two eccentricities e ₁ and e _{2 of} the mirrors, spherical aberration and coma of the mirror lens are corrected.

- The implementation of the collective in the form of a negative biconcave lens with an optical power ϕ _to / ϕ, together with the projection lens, transfers the image of the exit pupil of the lens - (the image of the main mirror through the second convex mirror) into space, near the optoelectronic receiver at a distance of 20-30 mm from it surface, in particular, in the present invention, the distance is 25 mm or 0.01-0.02f'.

Implementation of the collective in the form of a biconcave lens with an optical power f ₁ that satisfies the condition: 40 < |ϕ _to /ϕ| < 80, where ϕ is the optical power of the entire mirror-lens objective, allowed the Seidel aberration sums for spherical aberration, coma and astigmatism to obtain negative values and, together with the projection lens, to correct the projections of the aperture diaphragm - the surface of the main mirror onto the entrance window of the cryostat. This made it possible to exclude background illumination from reaching the optical-electronic receiver and to increase the signal-to-noise ratio of the system.

The lens projection lens, together with the team, performs two tasks.

The first one, in the mode of projection of a distant object onto the optoelectronic receiver, corrects the residual curvature of the image of the mirror lens and forms an image of the aperture diaphragm on the cryostat window near the optoelectronic receiver.

The second one projects the aperture diaphragm onto the cryostat window.

In both modes, the aberrations at the optoelectronic receiver and in the cryostat window plane were corrected.

This is achieved by making the lens projection lens of two components I and II.

In this case, the shapes of the lenses and their optical powers have the form:

20 < ϕ _I /ϕ < 40 14 < ϕ _II,1 / ϕ < 22

4 < ϕ _II,2 /ϕ < 8 18 < ϕ _II,3 / ϕ < 30

0.8 < ϕ _I / ϕ _II < 1.2,

In particular, in the I-th projection mode, the collective introduces small spherical aberration and coma, and large positive astigmatism and image curvature.

Both are compensated by the first component of the projection lens, which has negative astigmatism and image curvature.

In the second operating mode of the system, the collective has large positive values of spherical aberration, coma and astigmatism, zero image curvature, which are compensated by the second lens of the second II-th component of the lens projection lens.

Thus, the combination of the above features allows us to solve the problem.

The present invention is illustrated in the drawings, where in Fig. 1 - presents the optical scheme of the mirror-lens objective, Fig. 2 shows graphs of the frequency-contrast response, as well as the Appendix, which shows the parameters and optical characteristics of a particular sample.

The mirror-lens lens consists of a mirror lens 1, consisting of the main concave mirror 2, the second convex mirror 3 of a hyperbolic shape, a lens projection lens 4, a collective 5 located near the intermediate image plane 6 of the mirror lens 1 and an optoelectronic receiver 7.

Lens projection lens 4 consists of two components 8 and 9, the first 8 of which is a positive meniscus, convexly facing the image plane, the second component 9 consists of three lenses, of which the first lens 10 is biconvex, the second lens 11 is a negative meniscus, facing the convexity to the image plane, the third lens 12 is a positive meniscus facing the concavity to the image plane.

Between the third lens 12 of the second component 9 and the optoelectronic receiver 7, a cryostat 13 is installed with an entrance window 14, which is the exit pupil of the entire lens as a whole, coupled with the aperture diaphragm of the lens - the main concave mirror 2.

The work of the proposed mirror-lens objective is carried out as follows.

The rays emanating from an infinitely distant object after reflection from the main concave mirror 2 and the second convex mirror 3 are formed in the plane of the intermediate image 6 of the mirror lens 1.

The team 5 together with the lens projection lens 4 reproject the intermediate image into the plane of the optical-electronic receiver 7, where the image of the object is recorded.

Since all structural elements surrounding the optoelectronic receiver 7 (body, lens frames, mechanical elements, etc.) are sources of IR radiation, a background is created on the optoelectronic receiver 7 that is many times greater than the signal from the object. To exclude the background, it is necessary to exclude all non-working radiation sources. For example, cool to a temperature at which the wavelength λ _f radiation is less than the operating wavelength (λ _p ): λ _f << λ _p .

Let us consider a working “light tube” limited on one side by the diameter of the aperture diaphragm, and on the other hand by the diameter of the image of the working field, in our case, this is the diameter of the main concave mirror 2 and the diameter of the intermediate image 6.

If the "light tube" is redesigned into the space of the optoelectronic receiver 7, then it will occupy a volume limited on the one hand by the window 14 of the cryostat 13 - the image of the aperture diaphragm, and on the other hand by the size of the optoelectronic receiver 7.

If the received volume from the window 14 to the optoelectronic receiver 7 is cooled, then no rays that cause the background will fall on the optoelectronic receiver 7.

Thus, in the proposed mirror-lens lens, an increase in the resolution of the lens has been achieved by reducing aberrations in the pupils and increasing the relative aperture and the angular field.

INFORMATION SOURCES

1. Russian Federation, patent for invention No. 2670237, IPC: G02B 17/08, G02B 23/00, 10/19/2018

2. Russian Federation, utility model patent No. 41161, IPC: G02B 17/06, 10.10.2004 - prototype.

APPENDIX

Mirror lens:

- spectral range - 3-5 microns;

- focal length of the mirror lens - f'=2000 mm;

- the diameter of the entrance pupil - the diameter of the aperture diaphragm, the diameter of the main mirror - 500 mm;

- linear image size - 19.7 mm;

- diameter of the exit pupil, the diameter of the entrance window of the cryostat - 6.35 mm;

- distance from the exit pupil to the focal plane, the plane of the optical-electronic receiver - 25.7=0.013f';

- main mirror:

R _o \u003d 1613 mm, e ₁ ² \u003d 1.3224

secondary mirror

R _o =1007.7 mm, e ₂ ² =11.5383;

- Distance between mirrors - 522.69 mm;

- optical powers of lens components:

|ϕ _to /ϕ|=76.9;

_ϕI /ϕ=34;

ϕII _,1 /ϕ=17.9;

ϕII.2 _/ϕ=6.47 ;

ϕII.3 _/ϕ=25.25 ;

_ϕI / _ϕII =1,2,

Lenses with optical powers: ϕ _to ; φ _I ; ϕ _II,1 ; ϕ _II,3 are made of zinc selenide (ZnSe), the lens with ϕ _II,2 is made of fluorite CaF ₂ .

In FIG. 2 shows graphs of the frequency-contrast response.

Claims (7)

Mirror-lens lens containing a mirror lens consisting of a main concave mirror and a second hyperbolic convex mirror installed in series, a lens projection lens with an optical axis aligned with the optical axis of the mirror lens, in the plane of the intermediate image of the object created by the main concave and second convex mirrors , a collective is installed, and in the plane of its image an optoelectronic receiver, characterized in that the main concave mirror is made hyperbolic, the collective is made in the form of a biconcave lens with an optical power ϕ _to satisfying the condition: 40 < |ϕ _to /ϕ| < 80, where ϕ is the optical power of the entire mirror lens, the lens projection lens is made of two components, the first of which is a positive meniscus, convexly facing the image plane, with an optical power ϕ _I , the second component is made of three lenses, of which the first lens is biconvex with optical power ϕ _II,1 , the second lens is a negative meniscus, convexly facing the image plane, with optical power ϕ _II,2 , the third lens is a positive meniscus, concavity facing the image plane, with optical power ϕ _{II, 3} , while the optical powers of the lenses satisfy the condition: 20 < _ϕI /ϕ < 40, 14 < ϕ _II,1 / ϕ < 22, 4 < ϕ _II,2 /ϕ < 8, 18 < ϕ _II,3 / ϕ < 30, 0.8 < ϕ _I / ϕ _II < 1.2, in addition, the lens is supplemented with a cryostat, and the exit pupil of the lens is aligned with the cryostat window and located at a distance of no more than 0.01÷0.02f' from the optoelectronic receiver.

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