RU2567444C1 - Optical thermal imaging system for mid-infrared spectral region - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: optical thermal imaging system comprises, arranged on a beam path, an input lens which constructs a real intermediate image and a projection lens placed in front of a photodetector. The input lens has two components in the form of two series-arranged positive and negative menisci which face the object space with their convex side. The projection lens has three components made from, arranged in series on the beam path, a first negative meniscus, a biconvex lens and a third positive meniscus facing the object space with its convex side.

EFFECT: fewer optical elements with diffraction-limited image quality.

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Description

The invention relates to optical instrumentation and can be used as an optical system for various devices, for example, an optical system of a thermal imaging camera.

A known optical system for the infrared region of the spectrum described in patent RU No. 2338227, IPC G02B 13/14, G02B 9/64, publ. 02/20/2008. This optical system has a remote pupil, but its aberrations are corrected for the far infrared region of the spectrum, which does not allow using it for the middle infrared region of the spectrum, in addition, it has a large number of lenses, which complicates the technology of its production.

An optical system for thermal imaging devices is also known, described in patent RU No. 2449328, IPC G02B 13/14, G02B 23/12, publ. 04/27/2012, and an optical system with a remote aperture diaphragm for the mid-IR range in patent RU No. 2419113, IPC G02B 13/14, G02B 9/64, publ. 05/20/2011. Both optical systems have a large number of lenses, which reduces the transmittance of these systems and complicates the technology of their production.

The closest analogue to the claimed technical solution is the optical system of a thermal imaging device according to the patent for utility model RU No. 131206, IPC G02B 13/14, publ. 08/10/2013. The optical system of a thermal imaging device contains an input lens sequentially located along the rays, constructing a valid intermediate image containing a negative meniscus convex to the space of objects, a positive meniscus convex to the space of objects, a negative meniscus convex to the plane of the actual intermediate image, and a projection a lens mounted in front of the photodetector comprising sequentially mounted along the beam first positive meniscus second negative meniscus facing convex toward photodetectors, and the third positive meniscus convexity to the space objects, and a fourth positive meniscus convexity to photodetectors and disposed between the third meniscus lens and the projection photodetecting device. The disadvantages of this optical system are a large number of optical elements, which makes its production low-tech, and also reduces transmittance, which limits operational characteristics.

The objective of the invention is the creation of an optical thermal imaging system for the middle infrared region of the spectrum with improved technological and operational characteristics.

The technical result is a reduction in the number of optical elements while ensuring diffraction-limited image quality by changing the shape of the lenses and optimizing aberrations.

This is achieved by the fact that in the optical thermal imaging system for the mid-IR region of the spectrum, containing an input lens located along the rays, constructing a real intermediate image made of negative and positive menisci, convex to the space of objects, and a projection lens mounted in front of the photodetector and made of sequentially installed along the rays of the first meniscus, the second component and the third positive meniscus, convex space objects, in contrast to the known, the input lens, the two components, the first of the ray path is a positive meniscus, and a projection lens three components, wherein the first meniscus negative and is convex toward the object space, and the second component - a biconvex lens.

In FIG. 1 is an optical diagram of the proposed optical thermal imaging system for the mid-infrared region, FIG. 2 is a graph of the Strehl number, in FIG. 3 is a graph of field curvature and distortion.

The optical thermal imaging system for the mid-IR region of the spectrum (Fig. 1) consists in the direction of the rays from the input lens 1, which constructs an intermediate real image and a projection lens 2, behind which the photodetector 3 is installed. The input lens 1 is made in the form of a positive meniscus 4 and negative meniscus 5, convex to the space of objects. The projection lens 2 is mounted in front of the photodetector 3 and contains a negative meniscus 6, which is convex to the space of objects, a biconvex lens 7, and a positive meniscus 8, which is convex to the space of objects, sequentially installed along the rays. The input window 9 is part of the design of the photodetector 3, the cooled diaphragm 10 limits the aperture of the rays incident on the sensor array 11 of the photodetector 3.

An optical thermal imaging system for the mid-IR region of the spectrum works as follows: the light flux emanating from an infinitely distant point of the object hits the first surface of the input lens 1, passes through the menisci 4, 5, forms an intermediate image, then the light flux hits the first surface of the projection lens 2, passes through the meniscus 6, the biconvex lens 7, the meniscus 8, through the input window 9 enters the photodetector 3 and forms an image of the object on the sensor matrix 11.

In accordance with the proposed solution, a specific optical system was calculated, the design parameters of which are given in table 1.

Characteristics of the calculated optical thermal imaging system for the mid-IR region:

focal length f ′ = 200 mm

relative aperture 1: 4

field of view angle 2ω = 3.5 °

Figures 2, 3 show plots of the Strehl number for the center and edge of the field, depending on the amount of defocusing and the aberration plots of the calculated optical thermal imaging system.

The proposed optical thermal imaging system for the mid-IR region of the spectrum has high image quality, as evidenced by the Strehl graphs (Fig. 2) - the optical system has diffraction-limited image quality for the axis and edges of the field of view, and graphs of the curvature of the field and distortion (Fig. 3) - astigmatism is not more than 0.14 mm, distortion is not more than 0.6%.

Thus, a technical result was achieved - an optical thermal imaging system was created for the mid-IR region of the spectrum with a reduced number of optical elements, while the system has diffraction-limited image quality.

Claims (1)

An optical thermal imaging system for the mid-IR region of the spectrum, containing an input lens located along the rays, building a valid intermediate image and made of negative and positive menisci convex to the space of objects, and a projection lens mounted in front of the photodetector and made of sequentially mounted the path of the rays of the first meniscus, the second component and the third positive meniscus, convex to the space of objects, characterized in that there are two components in the input lens, with the positive meniscus being the first in the direction of the rays, and three components in the projection lens, while the first meniscus is negative and convex to the space of objects, and the second component is a biconvex lens.

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