RU2798087C1 - Mirror lens - Google Patents

Abstract

FIELD: optics.

SUBSTANCE: mirror lens contains two correction elements, a convex and a concave mirror, a two-lens aplanatic corrector and an aperture diaphragm on the spherical surface of the convex mirror, the annular zone of the concave mirror is located on the second spherical surface of the first correction element, the convex mirror is located on the first spherical surface of the second corrective element. Corrective elements and corrector lenses are made of the same optical material. Relations between the radii of curvature of the convex and concave mirrors and the diameters of the aperture diaphragm and the convex mirror are satisfied.

EFFECT: possibility of constructing an image in one plane for UV, visible and IR ranges of the spectrum from 0.15 to 10 µm with the same value of the focal length in different spectral ranges, protection of the input aperture from external influences, fastening of a convex mirror without vignetting of light beams, increasing aperture ratio and maintaining a wide field of view.

1 cl, 1 dwg, 1 tbl

Description

The present invention relates to the field of optoelectronic engineering and can be used in optoelectronic devices as a receiving lens operating in a wide spectral range of 0.15÷10 μm without refocusing and without the use of complex aspherical surfaces.

Known catadioptric system (patent RU 2446420 C1, publ. 27.03.2012), consisting of two hyperbolic mirrors and containing a lens corrector in the form of a single lens of the material BaF ₂ installed near the focal plane. The catadioptric system, made using a Ritchey-Chrétien mirror scheme, provides a high-quality image in the spectral range from 0.4 to 12.0 μm and an angular field of view of 1° with a relative aperture of 1:3 and a focal length of 1800 mm. Aberration correction was performed for the entire working spectral range.

The disadvantage of this catadioptric system is the presence of two aspherical surfaces, the absence of the UV spectral range, a small field of view (1°), low aperture ratio (1:3) and the need for refocusing when moving from one spectral range to another, which must be taken into account either by introducing a focusing shift , or in the design of a rotary device with replaceable radiation receivers. The change in the position of the image plane for different spectral ranges is due to the use of one lens in converging beams of rays as a field aberration corrector, which also does not ensure the equality of focal lengths for different spectral ranges. In addition, a catadioptric system made using the Ritchey-Chrétien mirror scheme must be equipped with a protective element in front of the entrance aperture and hoods on the primary and secondary mirrors to prevent spurious illumination, which complicates the design of the optical system. Mounting a secondary (convex) mirror requires the introduction of structural elements that partially overlap the light beams, thereby introducing additional vignetting.

Known optical system for ultraviolet, visible and near infrared spectral ranges (Vladimirov V.M., Yukseev V.A., Lapukhin E.G. Optical system for remote sensing in the UV, visible and near infrared ranges. Computer optics, No. 2 , volume 44, 2020), consisting of two hyperbolic mirrors and containing a two-lens corrector in converging beams of rays, which includes positive and negative elements with equal and opposite optical powers, which are made from the same brand of glass - fused quartz of the KI grade. The optical system, made using the Ritchey-Chretien mirror scheme, provides a focal length of 5539 mm, a relative aperture of 1:5.5 and an angular field of view of 4° in the spectral range from 0.2 to 3.3 μm. The two-lens corrector makes it possible to correct aberrations in one plane for the entire working spectral range.

The disadvantage of this optical system is the presence of aspherical surfaces, a small field of view (4°) and low aperture (1:5.5), which limits the use in the far IR range at wavelengths above 3.3 microns due to diffraction limitations. An optical system based on the Ritchey-Chrétien mirror scheme requires the installation of a protective element in front of the entrance aperture and the presence of hoods on the primary and secondary mirrors to prevent spurious illumination, which complicates the design of the optical system. The fastening of the secondary (convex) should contain structural elements that will partially block the light beams and introduce additional vignetting.

Known mirror-lens lens (Dobrunov S.V., Polessky A.V., Semenchenko N.A., Smirnova E.A., Shketov A.I. Mirror-lens lens for measuring photoelectric coupling in the IR range. Proceedings of the XXIII International Scientific and Technical Conference on Photoelectronics and Night Vision Devices - M.: JSC "NPO Orion", 2014), containing two spherical mirrors and a two-lens afocal compensator in parallel beams of rays (in front of the entrance pupil of the lens. A mirror-lens lens made with using the Schwarzschild mirror scheme, provides high resistance to flare and does not require the use of protective hoods in front of the entrance aperture.The afocal compensator is installed in front of the entrance aperture, provides correction of axial beam aberrations and serves as a protective window. visible range of the spectrum.

The disadvantage of this mirror-lens objective is the absence of the UV spectral range and a small field of view due to the metrological specifics of the application (the image of a 0.2 mm aperture was simulated). Mounting the main (convex) mirror requires the introduction of structural elements that partially block the light beams and introduce additional vignetting.

A two-mirror lens of the recognition channel is known in an optoelectronic complex observation and recognition system operating in the UV, visible and IR regions of the spectrum (patent RU 2305303 C2, publ. 27.08.2007), containing the main mirror, made in the form of an annular segment with a convex spherical surface , an aplanatic corrector in the form of an external spherical mirror annular zone, and a matrix radiation receiver. It also contains a protective window in the form of a fairing with spherical surfaces and with a spectral transparency range of 0.235 ... 3 μm, which simultaneously carries an annular zone of a mirror aplanatic corrector on the second spherical surface. A two-mirror lens of the recognition channel with an entrance window in the form of a radome with spherical surfaces ensures the construction of an image in one plane for all spectral ranges. With a focal length of the lens of the recognition channel F=120 mm and a geometric relative aperture of 1:0.8, a field of view of 1.5° is achieved. The version of the two-mirror lens of the recognition channel, made using the Schwarzschild mirror scheme, is closed from external influences by a spherical protective window, provides high resistance to flare and does not require the use of protective hoods.

The disadvantage of this two-mirror recognition channel lens is the small field of view (1.5°). The design of the lens also becomes more complicated, since the mounting of the main (convex) mirror requires the introduction of structural elements that partially block the light beams and introduce additional vignetting.

The closest in technical essence is a mirror-lens objective (patent RU 188678 U1, published on April 22, 2018), consisting of two spherical, convex and concave, concentric mirrors, in the center of curvature of which there is an aperture diaphragm with a double-glued aplanatic meniscus installed near it, the lenses of which are made of optical materials with a difference in refractive indices for the average wavelength not exceeding 0.001, and a difference in the average dispersion coefficients exceeding 20. blend, allows you to create mirror-lens objectives for various applications for the visible, UV and IR regions of the spectrum. In the version of the mirror-lens objective, its aplanatic meniscus is made with lenses made of STK9 and TF4 glasses and achromatized in the visible range of the spectrum. The focal length is 100 mm, an angular field of view of 20° is provided with a geometric relative aperture of 1:2.5. The value of the effective relative aperture reaches a value of 1:2.8.

The disadvantage of this mirror lens is the need to manufacture different versions of the lens for different spectral ranges - UV, visible or IR, which is due to the use of an aplanatic meniscus in converging beams of rays as a field aberration corrector, as well as a small value of the effective relative aperture. The mirror-lens objective, made using the Schwarzschild mirror scheme, is open to external influences and requires the installation of a protective element in front of the entrance aperture. Mounting a spherical convex mirror requires the introduction of structural elements that partially block the light beams and introduce additional vignetting, which will further reduce the value of the effective relative aperture.

The objective of the present invention is to ensure the construction of an image in one image plane for the UV, visible and IR spectral ranges from 0.15 to 10 μm, maintaining the same focal length in different spectral ranges, increasing the effective relative aperture, simplifying the technological and design of the mirror image. lens objective, providing protection of the input aperture from external influences without vignetting by the fastening elements of a spherical convex mirror, ensuring the required image quality and maintaining a wide field of view.

The technical result, due to the task, is achieved by the fact that in a mirror-lens lens consisting of two spherical mirrors, convex and concave, an aperture diaphragm and an aplanatic corrector made of two lenses, in contrast to the known one, the aperture diaphragm is located on the spherical surface of the convex mirror, the aplanatic corrector is made in the form of a compensator, close to afocal and consisting of positive and negative lenses with an air gap between them, the first correction element is installed in front of the entrance aperture, made in the form of a negative convex-concave meniscus with spherical surfaces, which simultaneously bears on the second spherical surface an annular zone of a concave mirror, between the spherical concave mirror and the aplanatic corrector a second correction element is installed in the form of a convex-concave meniscus with spherical surfaces, which simultaneously carries a convex mirror on the first spherical surface, and the first and second correction elements and lenses of the aplanatic corrector are made of material with the same refractive and dispersion indices, while in a mirror-lens objective, the following relations take place:

where: r ₁ - radius of curvature of the convex mirror;

r ₂ - radius of curvature of the concave mirror;

∅ _A.D. - aperture diaphragm diameter;

∅ _{Issue DSLR} is the diameter of the convex mirror.

The scheme of the mirror-lens objective is shown in Fig. 1.

The mirror-lens objective consists along the rays of the first correction element 1, a convex mirror 2, a concave mirror 3, a second correction element 4, the first lens of the aplanatic corrector 5, the second lens of the aplanatic corrector 6 and a matrix radiation receiver with a protective glass 7. Aperture diaphragm 8 located on the spherical surface of a convex mirror 2.

The design parameters of the mirror-lens objective are given in the table.

The parameters of the mirror-lens lens are as follows:

- working spectral range: 0.15…10.0 µm;

- focal length:

- for λ _UV =0.2 µm: F _o6 =50.099 mm;

- for λ _Vis =0.6 µm: F _rev =50.087 mm.

- for λ _MWIR =1.5 µm: F _rev =50.080 mm.

- for λ _MWIR =4.0 µm: F _rev =50.06 mm.

- for λ _LWIR =8.5 µm: F _rev =49.91mm.

- angular field of view: 20.3°;

- linear field of view: 18.0 mm;

- geometric relative aperture: 1:2;

- effective relative aperture: 1:2.4;

- distortion: ~0.9%;

- vignetting: ~33%

- length along the optical axis: 102.4 mm.

The principle of operation of a mirror-lens lens is as follows:

Parallel beams of light pass through the first correction element 1, made in the form of a negative meniscus, and fall on a spherical convex mirror 2, after reflection from which they fall on a spherical concave mirror 3, which is an annular zone on the second spherical surface of the first correction element 1. Spherical concave the mirror 3 forms a converging beam, in which the second correction element 4 with spherical surfaces is installed, the central zone of the first spherical surface of which is a convex mirror 2. After the second correction element 4, the light beams pass through the aplanatic corrector from the positive lens 5 and the negative lens 6 and finally formed the image falls on the matrix radiation detector with protective glass 7. The aperture diaphragm 8 is located on the spherical surface of the convex mirror, which allows minimizing the central shielding and providing a high value of the effective relative aperture. The first and second correction elements 1 and 2, together with the aplanatic corrector 5 and 6, minimize the values of chromatic aberrations in a wide spectral range from 0.5 to 10 μm due to the fact that they are made of a material with the same refractive and dispersion indices, and a convex 2 and concave 3 spherical mirrors form the necessary optical power, while in the mirror-lens objective, the following relations take place:

where: r ₁ - radius of curvature of the convex mirror;

r ₂ - radius of curvature of the concave mirror;

∅ _A.D. - aperture diaphragm diameter;

∅ _{Issue DSLR} is the diameter of the convex mirror.

The location of the annular zone of the concave mirror 3 on the second spherical surface of the first correction element 1 allows the element 1 to also serve as a protective window, which ensures the protection of the entrance aperture from external influences. The location of the convex mirror 2 on the first spherical surface of the second correction element 4 eliminates any additional vignetting, since there are no mechanical fastening elements of the convex mirror 2 that block the light beams.

Such a mirror-lens objective provides imaging in one plane for the UV, visible and IR spectral ranges from 0.15 to 10 μm, maintains the same focal length in different spectral ranges, increases the effective relative aperture, simplifies the technological and design of the mirror image. lens objective, provides protection of the input aperture from external influences without vignetting by the fastening elements of a spherical convex mirror, provides the required image quality and maintains a wide field of view.

The calculation of the image quality of a mirror-lens objective was carried out for use with a matrix photodetector, which has a photocathode diameter of ∅18 mm, a resolution of 40 lines/mm in the spectral range of 0.15÷5.5 μm and 20 lines/mm in the spectral range of 7.5 ÷10.0 µm. The calculated values of the contrast characteristics - contrast transfer coefficients (CPC) of a mirror-lens objective in one image plane are as follows: - for Δλ=0.15÷5.5 µm:

- for a point on the axis (diffraction quality): CPC=66.9%;

- for a point on the axis (aberration quality): CPC=57.8%;

- for the extreme point of the field ∅18 mm: PDA _M = 16.6%, PDA _C = 23.4%. - for Δλ=7.5÷10.0 µm:

- for a point on the axis (diffraction quality): CPC=22.0%;

- for a point on the axis (aberration quality): CPC=12.5%;

- for a field point ∅6 mm: PDA _M = 9.8%; CPC _C = 8.7%.

A field of view of 20.3° corresponds to the design of an image intensifier tube with a diamond photocathode ∅18 mm with a sensitivity range from 0.15 to 5.5 µm, and in the long term to the far IR range from 7.5 to 10.0 µm. In the version of the photodetector with the spectral range Δλ=7.5÷10.0 µm, refocusing is possible with the photocathode plane moving by minus 0.1 mm, while the image quality indicators increase to the diffraction level and will be the following values:

- for a point on the axis (diffraction quality): CPC=22.0%;

- for a point on the axis (aberration quality): CPC=19.8%;

- for a field point ∅6 mm: PDA _M = 17.2%; CPC _C = 16.8%.

As can be seen from the calculations, the mirror-lens objective, with its simple design, effective aperture of 1:2.4, and sufficient angular field of view (20°), provides an acceptable level of image quality in UV, visible, shortwave IR, midwave IR, and far IR. ranges of the spectrum in one image plane without refocusing.

Claims (7)

Mirror-lens objective, consisting of two spherical mirrors, convex and concave, an aperture diaphragm and an aplanatic corrector made of two lenses, characterized in that the aperture diaphragm is located on the spherical surface of the convex mirror, the aplanatic corrector is made in the form of a compensator close to afocal, consisting of positive and negative lenses with an air gap between them, the first correction element is installed in front of the entrance aperture, made in the form of a negative convex-concave meniscus with spherical surfaces, which simultaneously bears an annular zone of a concave mirror on the second spherical surface, between the spherical concave mirror and the aplanatic the corrector has a second correction element in the form of a convex-concave meniscus with spherical surfaces, which simultaneously carries a convex mirror on the first spherical surface, and the first and second correction elements and lenses of the aplanatic corrector are made of a material with the same refractive and dispersion indices, while in a mirror-like lens objective there are relations

where r ₁ is the radius of curvature of the convex mirror; r ₂ - radius of curvature of the concave mirror; ∅ _A.D - aperture diaphragm diameter; ∅ _{Convex mirror} - diameter of a convex mirror.

Images