RU2475787C1 - Dual band infrared high-aperture lens - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: lens has three components arranged in series on the beam path. The first and third components are positive menisci made from the same material whose concave surfaces face the image plane. The second component is negative with optical power of -(0.15-0.5) and comprises a negative meniscus and an additional negative and a positive meniscus with relative optical power values which are quasiequal on modulus, respectively lying on both sides of the negative meniscus. The menisci of the second component face the image plane with their concave surfaces; two of them are made from material different from material of the first and third components and have in spectral ranges 3-5 mcm and 8-12 mcm, average dispersion coefficients which differ by more than fivefold, with quasiequal partial dispersion coefficients values. Menisci on the beam path have the following optical power values, respectively: (0.6-0.7); -(0.6-0.9); -(0.1-0.25); (0.5-0.7); (0.65-0.85).

EFFECT: widening the operating spectral range from 3 mcm to 12 mcm, providing a fixed position of the image plane for operating spectral ranges of 3-5 mcm and 8-12 mcm, high energy concentration factor in a spot with diameter of 0,015 mcm.

2 cl, 6 dwg

Description

The invention relates to the field of optical instrumentation, namely to lenses for the infrared (IR) region of the spectrum, and can be used in technological installations for verifying the parameters of matrix heat radiation detectors used in thermal imagers.

There is a limited number of lenses for the infrared region of the spectrum in which the condition for ensuring simultaneous operation in two spectral (thermal imaging) ranges and the presence of a high relative aperture (higher than 1: 0.8) are fulfilled.

The known lens [Pat. RU 2410733 C1, IPC G02B 13/14 (2006.01), G02B 9/64 (2006.01). Two-spectral infrared lens with an aperture diaphragm taken out into the space of images [Text]. / Khatsevich T.N., Tereshin E.A .; Applicants and patent holders Khatsevich T.N., Tereshin E.A. - 2010101899/28; declared 01/21/2010; publ. 01/27/2011, Bull. Number 3. - 16 p.: Ill.] For the infrared region of the spectrum, intended for thermal imaging devices based on cooled matrix radiation detectors sensitive in the ranges from 3-5 microns and from 8-12 microns. The first positive component consists of a negative meniscus facing a concave surface to the plane of the aperture diaphragm, a biconvex and biconcave lenses. The second component is five-lens positive. Between the first and second components, the third component is located - the positive meniscus facing the concave surface to the plane of the aperture diaphragm and located at a distance of not more than 0.15 of the focal length of the first component in front of the plane of the intermediate image. The lens components have spherical refractive surfaces made of gallium arsenide and KRS5 material. The focal length f 'of the lens is 171 mm, the relative aperture is 1: 3. The working spectral range is 3-12 μm, the image quality is diffractive both in the spectral range of 3-5 μm and in the spectral range of 8-12 μm with the image plane unchanged. The length along the optical axis from the first refracting surface to the image plane is 300 mm, i.e. is 1.75 of the focal length of the lens.

The disadvantage of this lens is its small relative aperture, which does not allow for a 90% concentration of energy in the scattering spot corresponding to the pixel sizes of modern MPI for thermal imagers.

The fastest infrared lens [Pat. RU 2348953 C1, IPC G02B 13/14 (2006.01) The infrared fast three-lens lens [Text] was chosen as the closest in technical essence to an analog (prototype). / Khatsevich T.N., Zhuravlev P.V .; applicants and patent holders Institute of Semiconductor Physics SB RAS (RU) - 2007138194/28; declared 10/15/2007; publ. 03/10/2009, bull. Number 7. - 9 p.: Ill.], With a relative aperture of 1: 0.75, containing three components, the first of which is positive, the second negative component and the third positive meniscus. The first and third menisci are turned concave to the plane of the images, the second to the space of objects. The first and third menisci are made of one material (germanium, refractive index 4.00), the second meniscus is made of zinc selenide (refractive index 2.41). The following relationships occur in the lens:

Ф ₁ = (0.6 ÷ 0.7) Ф, Ф ₂ = - (0.15 ÷ 0.5) Ф, Ф ₃ = (1.3 ÷ 2) Ф,

where f ₁ , f ₂ , f ₃ , f are the optical forces of the first, second, third menisci and the lens as a whole, respectively.

The focal length f 'of the lens is 35.49 mm, the relative aperture is 1: 0.75. The length along the optical axis from the first refracting surface to the image plane is 63.3 mm, i.e. is 1.75 of the focal length of the lens. The lens is designed for use with matrix receivers whose pixel size is 0.03 mm or more. An example of a specific implementation is given for the IR region of the spectrum of 8-12 microns, the main wavelength of 10 microns. At least 70% of the energy is concentrated in a spot with a diameter of 0.03 mm. The verification calculation of an example of a specific embodiment in the spectral range of 3-5 μm shows that the image plane shifts by 0.2 mm, while the fraction of energy in the spot of the indicated size drops to 30%. The chromaticity of the position in the spectral range of 3-12 μm is 0.3 mm, i.e. 1/118 of the focal length of the lens. With the claimed ratios between the design parameters in the closest analogue, it is possible to achieve an increase in the energy concentration coefficient in the spot with a diameter of 0.03 mm in the spectral range of 3-5 μm, but not more than 70%, while the quality in the spectral range of 8-12 μm decreases , and image planes for the spectral ranges of 3-5 μm and 8-12 μm are shifted along the axis.

The disadvantages of the prototype are the limited spectral range of operation, the shift of the image plane when moving from the spectral range of 8-12 microns to the range of 3-5 microns, a low energy concentration coefficient in the spot, the dimensions of which correspond to modern MPI (for example, with pixels of 0.015 mm). The device of the optical system of the lens contained in the prototype is such that the chromaticity of the position is not corrected in it, which at a high relative aperture leads to an increase in the size of the aberration scattering pattern and, as a result, the inability to achieve 90% energy concentration in a spot with a diameter of 0.015 mm for any of ranges 3-5 and 8-12 microns with a fixed position of the MPI relative to the lens along the axis. This fact does not allow the use of the prototype in technological installations for checking the parameters of matrix heat radiation detectors used in thermal imagers.

The objective of the invention is to provide a dual-band infrared aperture lens with an extended spectral range, with a relative aperture of at least 1: 0.7, providing an unchanged position of the image plane when operating both in the working spectral range from 3 to 5 μm and in the working spectral range from 8 to 12 microns and diffraction image quality in each of the indicated ranges, as well as the possibility of using this lens in technological installations for checking the parameter in matrix heat radiation detectors used in thermal imagers.

The technical result achieved in the inventive dual-band infrared fast lens is to expand the spectral range of operation from 3 to 12 microns, to ensure a constant position of the image plane for the working spectral ranges of 3-5 and 8-12 microns, in increasing the energy concentration coefficient to 90% in a spot with a diameter of 0.015 μm, the dimensions of which correspond to modern MPI, for the indicated working spectral ranges.

The objective is achieved in that the dual-band infrared fast lens contains three components sequentially located along the rays, the first and third of which are made in the form of positive menisci of the same material, facing concave surfaces to the image plane, the second is a negative component containing a negative meniscus, optical whose strength is - (0.15 ÷ 0.5), while the relative optical power of the first component is (0.6 ÷ 0.7), the refractive surfaces of the components The spheres are spherical, according to the invention, negative and positive menisci with quasi-equal absolute magnitudes of relative optical forces located respectively on both sides of the negative meniscus of the second component are additionally introduced into the second component, while the menisci of the second component are turned by concave surfaces to the image plane, two of them are made from materials different from the materials of the first and third components and having coefficients cp in the spectral ranges 3-5 and 8-12 μm days dispersion differs by more than 5 times, with quasi-equal values partial dispersion ratios, the relative optical powers meniscus lens in accordance with their arrangement along the beams are respectively

The first and third components of the lens are made of chalcogenide glass, and the menisci of the second component are made of germanium and lead fluoride.

The proposed device is illustrated by the following graphic materials:

figure 1 is an optical diagram of a two-spectral IR lens, where components 1, 3 are made in the form of positive menisci from the same material, facing concave surfaces to the image plane; component 2 is made of a positive meniscus 5 and additionally introduced negative and positive menisci 4, 6 with relative optical forces quasi-equal in absolute value and concave surfaces facing the image plane; lenses 4, 5 of component 2 are made of different materials;

figure 2 is a graph of longitudinal chromatic aberration for the spectrum range from 3 to 12 microns;

figa - frequency response for the mid-IR range;

figb - frequency response for the far infrared spectrum;

figa - function of the concentration of energy (FFE) in the spot for the average IR range of the spectrum;

figb - FKE for the far infrared spectrum.

The proposed device operates as follows. Component 1, lenses 4, 5, 6, component 2 and component 3 focus the radiation of the middle and (or) far spectral ranges coming from each point of distant objects located within the angular field determined by the size of the sensitive area of the uncooled MFP and the equivalent focal length of the components 1, 2, 3 and create a real image in the image plane of the lens, providing for each point of the object focusing on a spot of small size, comparable in magnitude to the scattering spot due to diffraction, p At the same time, the position of the image plane remains unchanged for both the middle and far IR ranges of the spectrum.

A five-lens infrared fast lens is shown as an example of a specific implementation. The focal length f 'of the lens is 40 mm, the relative aperture is 1: 0.75. The working spectral range is 3-12 microns. The length along the optical axis from the first refracting surface to the image plane is 76.5 mm, i.e. is 1.9 of the focal length of the lens, the rear focal length is 20 mm. The first and third components of the lens are made of chalcogenide glass (amtirl), and the menisci of the second component are made of germanium and lead fluoride. Table 1 shows the relative optical powers and characteristics of the lens materials.

Table 1 Material Options Component Lens Material F _Rel V _3-5 V _8-12 R _3-5 R _8-12 one one AMTIR1 0.70 198.33 116.94 0.39 0.52 2 four Germanyum -0.68 107.29 795.97 0.31 0.37 5 PBF2 -0.17 46.39 8.64 0.55 0.53 6 AMTIR1 0.58 198.33 116.94 0.39 0.52 3 3 AMTIR1 0.74 198.33 116.94 0.39 0.52

As follows from table 1, in a specific embodiment of the infrared fast five-lens lens in the spectral ranges of 3-5 and 8-12 microns, the average dispersion coefficients of the negative and positive menisci additionally introduced into component 2 differ in 795.97 / 107.29 = 7.41; 46.39 / 8.64 = 5.37, i.e. more than 5 times, and the coefficients of partial dispersions are close in magnitude, i.e. are quasi-equal quantities. The relative optical forces of the menisci in the lens in accordance with their location along the rays are, respectively: 0.7; -0.68; -0.17; 0.58; 0.74, which satisfies relation (1).

To confirm the high quality of the image provided by the proposed optical system of a two-spectral IR lens, the following are the characteristics that are most often used to evaluate image quality in similar optical systems.

Figure 2 shows a graph of longitudinal chromatic aberration for a wide spectral range from 3 to 12 μm, including both the middle and far infrared ranges. The nature of the longitudinal chromatic aberration curve indicates that an apochromatic correction is provided in the proposed lens in the indicated spectral range, while the residual longitudinal chromatism is 0.006 mm, i.e. 1/6660 of the focal length.

The plots of frequency response curves for the indicated operating spectral ranges are shown in FIGS. 3a and 3b, respectively, and the PCF plots are shown in FIGS. 4a and 4b, respectively, for a fixed position of the image plane. From the presented graphs it follows that the inventive two-spectral lens provides high image quality close to the diffraction limit in each of the spectral ranges with the image plane unchanged, in particular, 90% of the energy concentration in a spot with a diameter of 0.015 μm, the size of which corresponds to the size of a modern pixel, is provided on the axis MPI, which allows the use of the invention in technological installations for checking the parameters of matrix heat radiation detectors used in those plizovizory.

Claims (2)

1. A dual-band infrared fast lens containing three components sequentially located along the rays, the first and third of which are made in the form of positive menisci of the same material, facing concave surfaces to the image plane, the second is a negative component containing a negative meniscus, the optical power of which is - (0.15 ÷ 0.5), while the relative optical power of the first component is (0.6 ÷ 0.7), the refractive surfaces of the components are made spherical, distinguishing Take advantage of the fact that negative and positive menisci with quasi-equal absolute magnitudes of relative optical forces located respectively on both sides of the negative meniscus of the second component are additionally introduced into the second component, while the menisci of the second component are turned by concave surfaces to the image plane, two of them are made of materials different from the material of the first and third components and having coefficients of average dispersion in the spectral ranges of 3-5 and 8-12 microns, differing more than h I eat 5 times, with quasi-equal values of the coefficients of partial dispersions, while the relative optical forces of the menisci in the lens in accordance with their location along the rays are, respectively: (0.6 ÷ 0.7); - (0.6 ÷ 0.9); - (0.1 ÷ 0.25); (0.5 ÷ 0.7); (0.65 ÷ 0.85). 2. The lens according to claim 1, characterized in that the first and third components are made of chalcogenide glass, and the meniscus of the second component is made of germanium and lead fluoride.

Images