JPH03191835A - Infrared-ray optical apparatus - Google Patents

Abstract

PURPOSE:To make it possible to realize low noises without increasing the size of a cold shield by providing a cooling restriction which is cooled with a cooling device other than a device for cooling an infrared-ray detecting element and the cold shield between an infrared optical system and the cold shield. CONSTITUTION:The image of infrared-rays is formed with an infrared-ray optical system 1. Noise light to an infrared-ray detecting element 6 is shielded with a cold shield 7 which is cooled with a cooling device 9. At this time, a cooling restriction 12 which is cooled with a cooling device 13 is provided between the optical system 1 and the shield 7. The restriction is arranged so as to cover a solid angle allowing for an opening 7a of the shield and a solid angle allowing for an opening restriction 10 from the element 6. Noise light which is inputted into the element 6 from the background between the optical system 1 and the shield 7 is decreased in this way. Therefore, the agreement between the opening 7a and the opening restriction 10 is not required, and the compact shield 7 is used. Thus, the apparatus characterized by low noises and by the small decrease in amount of light around the element 6 can be constituted without increasing the thermal load of the device 9.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an infrared optical device that obtains, for example, an infrared image.

[Prior Art] FIG. 2 shows, for example, R.D. Hudson, Jr., “In
fraredSystem Engineering”
, John Vilcy & 5ons, 1969
This is a cross-sectional view showing a conventional infrared optical device shown in 1999, p. 354. In figure 1, 1 is an infrared optical system that images infrared rays, 2 is an infrared ray that is incident on the infrared optical system 1, and:
3 is a lens barrel that holds the infrared optical system 1; 4 is a Dewar bottle for obtaining a vacuum and low temperature state; 5 is a Dewar window provided at the opening on the infrared optical system side of the Dewar bottle 4; 6
4 is an infrared detection element such as an infrared solid-state image sensor in which minute elements are arranged in a two-dimensional array, and 7 is provided on the convex bottom of the Dua bottle 4, and 7 is an infrared detection element that prevents noise light from entering the infrared detection element 6. A cold shield for shielding, 8 is a housing that covers the dual bottle 4 and holds the lens barrel 3, 9 is a housing 8
This is a cooling device that is attached to the holder and has a cooling section inserted into four parts of the Dua bottle 4.

Next, the operation will be explained.

The infrared rays 2 incident on the infrared optical system 1 pass through the dual window 5 and the opening 7a of the cold shield 7, and form an image on the infrared detection element 6. The infrared detection element 6 is cooled by a cooling device 9 in order to obtain sensitivity. The space surrounded by the dure bottle 4 and dure window 5 is evacuated to efficiently cool the infrared detection element 6. The cold shield 7 is attached to the Dua bottle 4 and is cooled to the same extent as the infrared detection element 6, and the infrared rays emitted from the cold shield 7 are negligibly small compared to the infrared rays 2 to be detected. The opening lower a of the cold shield 7 allows the infrared rays 2a focused on the lower end 6a of the infrared detection element 6 and the infrared rays 2b focused on the upper end 6b of the infrared detection element 6 to be transmitted to the infrared detection element 6 without being obstructed by the cold shield 7. This is the diameter required to reach . Therefore, by installing the cold shield 7, the infrared rays transmitted through the infrared optical system 1 can be
In addition, the configuration is such that unnecessary noise light emitted from the room temperature background such as the mirror wJ3 and incident on the infrared detection element 6 is minimized. The noise light reduction efficiency η of the cold shield 7 is determined by the solid angle Ω6 looking into the open lower a of the cold shield 7 from the infrared detection element 6, and the infrared 2 imaged on the infrared detection element 6, as shown in the first equation. Solid angle Ω of the luminous flux. The ratio η=Ω. /Ω. It is expressed as +11. ηku1. In other words, Ω. 〈Ω. 2, noise light emitted from the lens barrel 3 enters the lower end 6a of the infrared detection element 6 within the solid angle indicated by hatching in FIG. Infrared detection element 6
Noise light is similarly incident at other points. Therefore η
] In addition to a decrease in the S/N of the detection signal, when the environmental temperature of the infrared optical device changes and the temperature of the lens barrel 3 increases, in the worst case, the output of the infrared detection element 6 may be caused by noise light. There is a risk that the signal will become undetectable due to saturation.

On the other hand, η〉1. In other words, Ω. 〉Ω. In this case, the noise light emitted from the lens barrel 3 does not directly enter the infrared detecting element 6, but the infrared 2 that passes through the infrared optical system 1 and forms an image on the infrared detecting element 6 passes through the cold shield 7. opening lower a
, and the signal light decreases. Therefore, the cold shield 7 with efficiency η=1 can reduce noise light most without reducing signal light. In other words, Ω. =Ω0.

An infrared optical device in which η=1 is obtained by matching the opening lower a of the cold shield 7 with the aperture stop of the infrared optical system 1. FIG. 3 shows, for example, R, E, Fische
r, Photonics 5pectra, p, 5
3-60 (198B) is a cross-sectional view showing a conventional infrared optical device in which the efficiency η of the cold shield 7 is 1, and in the figure, 1-9 are similar to the conventional example shown in FIG. It is something. 10 is an aperture stop of the infrared optical system 1, 11
is the optical axis of the infrared optical system 1.

In the infrared optical device shown in FIG. 3, the solid angle Ω of the open lower a of the cold shield 7 seen from the center of the infrared detection element 6. is determined by the F number of the infrared optical system 1.

Ω. =-Lgo (sr) (21F) Therefore, the noise light incident on the infrared detection element 6 is composed of the emitted light of the infrared optical system 1 itself and the faint radiation emitted from the cooled cold shield 7. Reduced to light.

[Problems to be Solved by the Invention] In the conventional infrared optical device shown in FIG. If not, it is given by the third formula (3). In the third equation, θ is the infrared detection element 6
This is the angle formed by the straight line connecting the upper end 6b of the aperture stop 10 and the center of the aperture stop 10, and the optical axis 11 of the infrared optical system 1.

From the third equation, the illuminance distribution of the infrared rays 2 on the infrared detection element 6 is such that θ is small, that is, the aperture diaphragm 10 and the infrared detection element 6
It can be seen that the larger the distance between them is compared to the size of the infrared detecting element 6, the more negative the difference becomes.

In order to obtain a low-noise infrared optical device in which the noise light emitted from the lens barrel 3 does not enter the infrared detection element 6, as explained above, the opening [7a] of the cold shield 7 must be connected to the infrared optical system 1. It is necessary to match the aperture 10 with the aperture 10. Therefore, in order to make the illuminance of the infrared rays 2 of the infrared detection element 6-■- nearly uniform, it is necessary to open the shield '7.
j 7 a and the infrared detection element 6 (hereinafter referred to as the height of the cold shield) must be made large, and the cold shield 7 becomes long. In addition, the solid angle looking into the opening 17a of the cold shield 7 necessary for the infrared rays 2 to enter the infrared detection element 6 without being restricted or blocked is as follows:
As shown in the second equation, it is determined by the F number of the infrared optical system 1, so as the height of the cold shield increases, the opening [1] also increases, and a large cold shield 7 is required2. When using an infrared solid-state image sensor in which minute elements are arranged in a two-dimensional array as the infrared detection element 6 to obtain an image, a large number of elements are used to obtain a wide-field, high-resolution image. Infrared solid-state imaging devices for dolls are being developed, and a fairly large coal shield 7 is required.

When the cold shield 7 is turned into a doll in this way, the cold shield 7 is attached to the Dua bottle 4.

The cooling device 9 has to cool the large cold shield 7 in addition to the large infrared detecting element 6, which poses the problem of increased heat load. Ta.

Furthermore, as the heat load on the cooling device 9 increases, the time required to cool the infrared light 2 (-6) to a predetermined temperature 2, for example, liquid nitrogen 411 degrees increases17. The problem was that it took time.

This invention has been made to solve the problems mentioned in -1-, and aims to provide an infrared optical device that can reduce noise without increasing the size of the cold shield.

An infrared optical device according to the present invention includes a cooling aperture that is cooled by a second cooling device that is separate from a cooling device that cools an infrared detection element and a cold shield. Install it between the and cold shield.

It is designed to cover the solid angle between the infrared detection element and the 11-1 of the cold shield and the solid angle that looks into the aperture stop of the infrared optical system.

[Function] The cooling aperture in the present invention is cooled by the second cooling device and reduces the noise light that enters the infrared detection element from the background between the infrared optical system and the cold shield. There is no need to match the aperture of the cold shield with the aperture of the infrared optical system, and by using a small cold shield, the thermal load on the cooling device that cools the infrared detection element and the cold shield can be increased. Therefore, it is possible to construct a low-noise infrared optical device in which the amount of light around the infrared detection element is less reduced.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing one embodiment of the present invention, and in FIG. 1, numerals 1 to 11 are the same as those in the conventional example.

]-2 is a cooling diaphragm installed so that the aperture diaphragm 10 of the infrared optical system 1 coincides with the side aperture 12a of the infrared optical system, and 13 is a second cooling diaphragm attached to the cooling diaphragm 12. The cooling aperture 1-2 in J- is a cooling device 1-:3.
The lens barrel 3 is attached to the inner wall of the housing 8 via a heat insulating material 14 . .

As indicated by diagonal lines in FIG. 1, the cooling aperture 12 has a solid angle Ω from the point of the infrared detection element 6-L to the open lower a of the shield 7. and the solid angle Ω looking into the aperture stop 10 of the infrared optical system 1. Ω, which is the difference between - Install so as to cover the area within the solid angle of Ω0. The inner wall of the cooling aperture 12 is coated with a velvet coating or the like to reduce the reflectance, so that unnecessary infrared rays emitted from the infrared optical system 1 and the lens barrel 3 are reflected on the inner wall of the cooling aperture 12 and detected by the infrared detection element. 6
prevent it from entering.

Since the cooling diaphragm 12 is installed in this way, unnecessary noise light that enters the infrared detection element 6 in addition to the infrared ray 2 that is the signal light to be detected is transmitted through the infrared optical system 1 and the cooling diaphragm 1.
2 and the cold shield 7.

The spectral radiance W(λ) of a blackbody whose absolute temperature is T.

T) is given by the fourth formula (%) (4). Here, λ is the wavelength of the emitted light, h is Blank's constant, is Boltzmann's constant, and C is the velocity of light dust. Fourth
From the formula, for example, when the wavelength λ of the radiation light is 4 μm, 2
The radiance at 0°C is 1/ of the radiance at 60°C.
It can be seen that the value is 4 or less. Therefore, the cooling diaphragm 12 does not necessarily need to be cooled to the same temperature as the infrared detection element 6, and by configuring the second cooling bag M13 with, for example, a Peltier element, and keeping the cooling diaphragm 12 at room temperature or below, the mirror Even if the temperature of the tube 3 rises, it is possible to prevent an increase in noise light.

When a Peltier element is used as the second cooling device 13,
Heat dissipation accompanying cooling of the cooling aperture 12 can be performed via the housing 8. In this case, in order to prevent the temperature of the lens barrel 3 and the infrared optical system 1 from rising due to heat radiation of the second cooling device 13! The lI cylinder 3 is attached to the housing 8 via a heat insulating material 14.

Also, lens barrel 3. By filling the space surrounded by the Dua bottle 4 and the housing 8 with dry gas such as nitrogen gas, dew condensation can be prevented even if the cooling aperture 12 is cooled to a low temperature below room temperature.

As described above, according to this infrared optical device, the opening lower a of the cold shield 7 does not need to coincide with the aperture stop 10 of the infrared optical system 1, so that the illuminance distribution of the infrared rays 2 on the infrared detection element 6 can be controlled. Even if the aperture diaphragm 10 is separated from the infrared detection element 6 for uniformity, there is no need to increase the height and size of the cold shield 7, and the infrared detection element 6 and the cold shield 7 can be cooled. The load on the cooling device 9 does not increase.

In the above embodiment, the aperture diaphragm 10 is provided between the infrared optical system 1 and the cold shield 7, and the case where []7a between the aperture diaphragm 10 and the cooling diaphragm 12 on the infrared optical system sides coincide is explained. However, even when the aperture stop 10 is located inside the infrared optical system 1, by installing the cooling stop 12 between the infrared optical system 1 and the cold shield 7, the lens barrel 3
It is possible to reduce the noise light emitted from the infrared light detecting element 6 and enter the infrared detecting element 6, and a similar effect can be obtained.

[Effects of the Invention] As described above, according to the present invention, between the infrared optical system and the cold shield, there is a solid angle at which the aperture of the cold shield is viewed from the infrared detection element, and an aperture stop of the infrared optical system. It is equipped with a cooling aperture that covers the solid angle and is cooled by a second cooling device, and is configured to reduce noise light that enters the infrared detection element from the background between the infrared optical system and the cold shield, so the background temperature does not rise. In addition, since the cold shield that is cooled together with the infrared detection element can be constructed with a small size, the heat load on the cooling device for the infrared detection element can be reduced and the time required for cooling can be reduced. It has the effect of shortening it.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a sectional view showing a conventional infrared optical device, and FIG. 3 is a sectional view showing a conventional infrared optical device with reduced noise. 1 is an infrared optical system, 2 is an infrared ray, 3 is a lens barrel, 4 is a dual bottle, 5 is a dual window, 6 is an infrared detection element, 7 is a cold shield, 7a is an opening in the cold shield, 8 is a housing, 9
10 is a cooling device, 10 is an aperture diaphragm, 11 is an optical axis, 12 is a cooling diaphragm, 13 is a second cooling device, and 14 is a heat insulating material. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] An infrared optical system that forms an image of infrared rays, an infrared detection element that is cooled by a cooling device, and is provided at an imaging position of the infrared optical system, and an infrared detection element that faces the infrared optical system side. In an infrared optical device comprising a cold shield having an aperture and shielding noise light from reaching the infrared detecting element, a three-dimensional structure is provided between the infrared optical system and the cold shield, and the infrared detecting element looks through the aperture of the cold shield. An infrared optical device comprising a cooling diaphragm that covers a solid angle between a corner and an aperture stop of an infrared optical system and is cooled by a second cooling device different from the above cooling device.