JPH0467896B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an infrared radiometer used as an infrared imaging device for ground use, aviation, or space, or a radiation thermometer.

[Conventional technology and problems]

Currently, many infrared detectors use a chipper to prevent problems even if a certain amount of unnecessary radiation (stray light) from the surroundings enters the detector and causes a drift in the detector output due to changes in ambient temperature. The signal light is converted to AC and the DC component of the detector output is removed (for example, "Infrared Engineering" by Henry L. Hackforth, co-translated by Masanobu Wada and Toyasu Nakano, 1963, Kindai Kagakusha, p102-109).

If a further reduction in stray light is required, a baffle is installed inside the dewar that houses the detector to block stray light. Furthermore, when an aperture is required, a blackened aperture is used.

In this way, many methods have been developed to modulate the signal light using a chopper and detect it in an AC manner, but an infrared radiometer that detects the signal light in a DC manner without using a chopper has not been put into practical use. It has not been.

However, when high-speed response is required, it is difficult to chop the signal light, and the signal light detection time is shortened by the time the chopper blocks the optical path, resulting in a low S/N ratio. It will drop.

Further, when a thermal image is acquired using a multi-element sensor such as an infrared CCD, it is not preferable to frequently insert choppers to block the signal light, as this may lead to image defects.

Cold sealing alone can reduce the effective FOV when the sensing element area is large, especially for multi-element sensors.
(Field of View: Figure 1) cannot be clearly defined. Currently, blackened apertures and cooled buttfuls (Figure 2) are used to determine the FOV. However, a blackened aperture at room temperature itself emits infrared rays, which is detected by the detector, which is undesirable.
If you make a Batsuful with sufficient performance, it will become large and difficult to cool.

[Purpose of the invention]

An object of the present invention is to provide an infrared radiometer with sufficient performance without using the above-mentioned chopper, buffer, or blackening aperture.

[Means and actions for solving problems]

FIG. 1 is a vertical cross-sectional view of the vicinity of the detection element of the Deyuwa, a concave mirror with a hole in the center (hereinafter referred to as mirror aperture), and a relay lens. The shaded area to the left of the detection element contains a cryogen such as liquid nitrogen, which cools down to the cold shield. The mirror aperture is placed so that the center of the sphere constituting the concave surface is near the detection element. A hole is made in the area through which the signal light passes, and is used as an aperture. The detection element sees external signal light only through the hole, and the hole acts as an aperture. The rest of the field of view sees a mirror image of the periphery of the element itself, which is cooled and at a low radiation level, due to the effect of reflection by the concave mirror.

By placing a mirror aperture as a diaphragm at a sufficient distance from the detection element, the exit pupil of the signal light to the detector can be clearly defined. This reduces the difference between the designed FOV and the field of view actually seen by the edge of the element. The field of view outside the FOV sees the low-temperature region around the detection element itself, so the level of stray light is low.

Figure 3 shows the results of estimating the mirror aperture effect using a single-element indium antimony detector (3 to 5 μm) and a gold-deposited concave mirror without holes. The angular distribution of the response of the detector to a point light source is expressed by integrating the solid angle from the incident angle of 90° to θ° and normalizing the total to 100%. The graph is drawn on one half, so the angles are expressed in half-width units. For example, the FOV of the detector used in the experiment is 25°, so a position of 12.5° on the horizontal axis corresponds to the geometric optical FOV. The value on the vertical axis there is 37
% and 37% of the total incidence from outside 12.5°
This indicates that the radiation enters as stray light. The experimental values of the response when using a concave mirror with f=70 mm and an angle of view of 19.4° (half-angle) and their correction values are represented by squares. The dotted horizontal line is the response when the dewar window is covered with a gold-deposited plane mirror. This state is similar to using a hemispherical mirror (the angle of view is 90 degrees), so the response value at this time shows that the radiation emitted by the gold deposited on the concave mirror and the radiation emitted by the window material (saphire) are the same as those of the concave mirror. The amount reflected and incoming was calculated and subtracted from the experimental value to obtain the corrected value. The correction values match well with the curve, indicating that the concave mirror blocks radiation within the field of view. Therefore, it is thought that mirror apertures also exhibit similar effects.

Figure 4 shows the optical system of a radiation thermometer incorporating a mirror aperture. The combination of a detector and mirror aperture that takes sufficient consideration to stray light (unwanted radiation from the surroundings) allows infrared radiation to be detected in a DC manner without the need for constant comparison with a reference radiation source using a chopper. can do.

〔Effect of the invention〕

By suppressing stray light that causes drift, the detector has high stability. Therefore, it is possible to continuously
The object can be observed in a DC manner, high speed can be obtained, and image loss can be prevented.

Even for elements with a wide light-receiving surface such as multi-element sensors, it can be used without using blackened apertures or rounded apertures.
FOV can be clearly defined. Therefore, unnecessary infrared rays from the blackening aperture are not detected, and there is no increase in the burden on cooling the buffer.

[Brief explanation of the drawing]

[FIG. 1 Mirror Aperture] FIG. 1 is a sectional view of the vicinity of the detection element of the deyuwa, the mirror aperture, and the relay lens. 1...Detection element, 2...Cold shield, 4
...Mirror aperture, 5...Relay lens, dotted line, designed FOV, dash-dotted line, field of view seen by the edge of the detection element. [FIG. 2 Buzzle] FIG. 2 is a vertical cross-sectional view of the vicinity of the detection element when a Buzzle is provided. The left side of the detection element is the outer wall of the deyuwa where the cryogen is placed. 1...Detection element, 6...Batsuful. [Figure 3: Solid angle integral of the angular distribution of the detector response from 90° to θ°] This is the result of confirming the background radiation suppression effect of the mirror aperture using a concave mirror. 7...Concave mirror experimental value, 8...Concave mirror correction value, dotted line, response when the Deyuwa window is covered with a gold-deposited plane mirror. [FIG. 4 Application Example to Radiation Thermometer] FIG. 4 is a cross-sectional view of a dewar, a mirror aperture, and an optical system that constitute the radiation thermometer. 1...Detection element, 2...Cold shield, 4
...Mirror aperture, 5...Relay lens, 9
...Objective lens.

Claims (1)

[Claims] 1 A concave mirror with a hole in the center is placed in front of the cooled infrared detector so that the center of the spherical surface is near the detection element, and the signal light is made to enter the detector through the hole in the concave mirror. Infrared radiometer.