JPH06273225A - Cold shield - Google Patents

Abstract

PURPOSE:To reduce a thermal load and to reduce a quantity of reflected/ scattered light, which is incident on a detector, of infrared rays on a cold shield inner wall by providing a groove consisting of a face, which is formed of lines binding the maximum effective diameter end of a material side opening face and each of N pieces of tops together, and a face, which is formed of lines binding the maximum effective diameter end of a light receiving face and each of the tops. CONSTITUTION:When a point of intersection between a straight line passing an optional point P in the inside 7 of a cold shield opening face and a face constituting a groove on a cold shield inner wall is set to be Q while an optional point on a detector 2 is set to be R, the groove takes such structure as there are one or more (N) points of intersection but the point Q for points of intersection between a segment PQ or a segment QR and the cold shield inner wall. Consequently, reflected/scattered light of infrared rays, which are incident on the groove 8 from the inside 7 of the opening face, is prevented from being incident on the detector 2 directly. Therefore, the reflected/scattered light, which is incident on the detector 2, of the infrared rays on the cold shield inner wall is extremely little, so that shot noise generated in the detector 2 can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, shielding an infrared imaging device.

[0002]

2. Description of the Related Art FIG. 6 is a sectional view showing a part of an infrared imaging device showing an example of use of a conventional cold shield. This cold shield is "Determining Background for Testi
ng Infrared Detectors ”, John David Vincent, LASER
This is a conventional example shown in S & OPTRONICS P64-65, JUNE 1991. In FIG. 6, 2 is an infrared detector (hereinafter referred to as a detector), 4 is a cold shield with a baffle, 5a is a front baffle, 5b is a first center baffle, 5c is a second center baffle, and 6 is incident from outside the field of view. Infrared, 10 is cold head, 13 is optical axis of optical system, 14
Is a cooler, 15 is an optical system, and 16 is infrared rays emitted from a target object.

The infrared image pickup device collects infrared rays 16 emitted from a target object with an optical system 15 to detect the infrared rays 16.
The photoelectric conversion is performed by. When the infrared rays incident on the detector 2 are photoelectrically converted, noise called shot noise that is proportional to the square root of the incident light intensity is generated. In particular, shot noise is dominant in an infrared imaging device having a circuit with reduced noise. Therefore, if the infrared rays received by the detector 2 are limited to the infrared rays 16 emitted from the target object as much as possible, the device noise can be reduced. A cold shield is used to reduce this noise. The cold shield 4 is a shield cylinder that limits the field of view of the detector 2 and shields the detector 2 from infrared rays emitted from the inside of the infrared imaging device or the like. The cold shield 4 is cooled in order to suppress infrared radiation from itself. For cooling, the cold shield 4 is attached to the cold head 10 cooled by the cooler 14. In addition, the inner wall of the cold shield 4 is coated with a high infrared absorptivity in order to prevent infrared rays 6 incident from outside the field of view from being reflected and scattered by the inner wall of the cold shield 4 and entering the detector 2.

FIG. 7 is a sectional view showing the effect of the baffle. In FIG. 7, 6a, 6b, and 6c are infrared rays that enter from outside the field of view. As shown in FIG. 7, the front baffle 5a inside the cold shield 4 has a role of preventing the infrared rays 6a from entering the inner wall of the cold shield 4. Baffle 5
When there is no a, the infrared ray 6a is reflected and scattered by the inner wall of the cold shield as shown by the broken line in FIG. 6, and a part thereof enters the detector. However, when the baffle 5a is provided, it is possible to prevent the infrared rays from directly entering the inner wall of the cold shield 4 and suppress the amount of infrared rays entering the detector 2. The first center baffle 5b has an effect of blocking the infrared rays 6b reflected / scattered by the inner wall from entering the detector 2. Further, like the front baffle 5a, the first center baffle 5b has a role of preventing infrared rays 6c from entering the inner wall of the cold shield 4. The second center baffle 5c plays the same role as the first center baffle 5b. As can be seen from the above description, the greater the amount of protrusion of the baffle from the inner wall of the cold shield 4 in the optical axis direction, the greater the amount of infrared rays reflected / scattered by the inner wall of the cold shield 4 and incident on the detector 2. It is also clear that the greater the number of baffles, the greater the effect.

Further, there is a conventional lens barrel inner wall of a camera or the like in which a fine groove is cut in order to suppress reflection / scattering of light in the barrel. FIG. 8 is an enlarged cross-sectional view of the groove provided in the lens barrel of the camera. Reference numeral 17 is a groove carved in the lens barrel, and 18 is light incident on the groove. This groove 17 has the following effects.

The light 18 incident on the groove 17 is reflected and scattered inside the groove 17 as shown in FIG.
There are multiple reflections inside 7. Considering only the reflection on the surface forming the groove 17, the light 18 is attenuated by the absorptance of the coating for each reflection, and the multiple reflections cause the attenuation depending on the number of reflections. Therefore, since multiple reflection occurs as compared with a surface having no groove, more light is absorbed by using the groove structure. Further, the groove structure has an advantage that the lens barrel can be miniaturized because it does not require an inward protruding portion unlike a baffle.

However, the infrared absorption effect may not be sufficiently obtained depending on the groove structure. FIG. 9 is a sectional view showing the former case. In FIG. 9, reference numeral 20 denotes a groove-forming surface, 2
Reference numeral 1 is the range of infrared rays incident on the surface 20, and 22 is the range of infrared rays 21 reflected and scattered outside the groove.

The infrared rays incident on the surface are reflected and scattered in a half space in the direction normal to the surface. In the case of the groove structure shown in FIG. 9, since a part of the detector 2 exists within the reflection / scattering range 22 of the infrared rays 21 incident on the surface 20, a part of the infrared rays 21 enters the detector. In the past, the structure of the groove was determined without considering the behavior of the reflected / scattered light on the surface forming the groove, so that the infrared absorption effect of the groove was not sufficiently obtained.

[0009]

In the conventional cold shield having the baffle, it is necessary to make a large amount of protrusion of the baffle from the inner wall of the cold shield in the optical axis direction in order to sufficiently obtain the effect of the baffle. Therefore, there is a problem that the cold shield becomes large and the cold head for cooling also becomes large, and the load of the cooler increases. In addition, the cold shield can be miniaturized by carving a groove on the inner wall of the cold shield, but depending on the groove structure, there is a problem that infrared rays reflected and scattered by the groove enter the detector and the infrared absorption effect is not sufficiently obtained. .

The present invention has been made to solve the above problems, and obtains a cold shield which has a small heat load and which reduces reflected / scattered light of infrared rays on the inner wall of the cold shield incident on the detector. The purpose is to

[0011]

The cold shield according to the present invention is a cone that connects the maximum effective diameter end of the object side opening surface and the maximum effective diameter end corresponding to the light receiving surface placed on the opposite side of the cold shield. A surface formed by a line connecting each of the N vertices from the maximum effective diameter end of the object-side opening surface with respect to arbitrary integer N ring-shaped vertices provided on the outside of the base surface,
A groove formed by a surface formed by a line connecting the above-mentioned apexes from the maximum effective diameter end of the light receiving surface was provided. Further, the groove is a surface inside a surface formed by a line connecting N apexes from the maximum effective diameter end of the object side opening surface and a surface formed by a line connecting each apex from the maximum effective diameter end of the light receiving surface. The inner surface and the inner surface. In addition, the groove is one or a plurality of spiral grooves continuously formed from a part of the object-side opening surface toward the learning surface-side opening surface.

Further, in the cold shield according to the invention of claim 4, a cone-shaped surface corresponding to the maximum effective diameter end of the light-receiving lens and the maximum effective diameter end corresponding to the light-receiving surface is set, and an outer edge is provided outside the corresponding cone-shaped surface. A plurality of concentric baffles are provided, and these baffles have a diameter corresponding to the diameter of the baffle on the light receiving surface side smaller than that of the baffle on the lens surface side. Furthermore, the equivalent of a truncated cone surface connecting the maximum effective diameter end of the light receiving lens and the maximum effective diameter end corresponding to the light receiving surface is set,
In the cold shield, the diameter corresponding to the light receiving surface side is smaller than the diameter corresponding to the lens surface side.

[0013]

In the cold shield according to the present invention, the incident light from the object or the light receiving lens side is shielded once from the light irradiated on the cold shield. Further, the cooling portion becomes smaller, and the cooling works effectively.

[0014]

【Example】

Example 1. FIG. 1 is a sectional view showing an embodiment of the present invention. In FIG. 1, the same symbols as those in FIGS. 6 to 8 indicate the same or corresponding portions. In FIG. 1, 1 is a cold shield of this embodiment. The cold shield 1 has an inner wall shape that is rotationally symmetrical with respect to the optical axis 13. Further, the grooves are carved at the same intervals in this embodiment. Hereinafter, since the inner wall shape is rotationally symmetrical with respect to the optical axis 13, the groove shape will be described for the left half of the optical axis 13. In FIG. 1, the inside of the cold shield 1, that is, the tip portion projecting toward the optical axis is called a mountain (represented by c and d in FIG. 1), and the tip portion projecting outward, that is, the tip farther from the optical axis is a valley. Call. One groove refers to a portion sandwiched between two adjacent peaks (c and d). Further, the groove is divided into two parts with a valley in between, and the opening surface 7 side is referred to as an upper surface and the detector 2 side is referred to as a lower surface. 8 is an arbitrary groove in the cold shield 1, 9 is a lower surface of the groove 8, and 11 is an upper surface of the groove 8. In this embodiment, the number of grooves N is 8,
The diameter of the cold shield is the same in the height direction of the figure, that is, between the opening surface 7 and the light receiving and detecting surface 2. Regarding the shape of this cold shield, if the structure in which the peak of the cold shield is outside the surface of the truncated cone that connects the maximum effective diameter end of the light receiving lens of the optical system and the maximum effective diameter end of the light receiving detection surface Good.

A method of determining the structure of the cold shield will be specifically described. As described above, the structure shown in FIG. 1 is used to facilitate manufacture, and the diameter of the cold shield at that time is assumed to be a size that does not prevent effective incident infrared light from reaching the detection surface. First, a line is formed by rotating a line connecting the outermost end b of the opening surface 7 and the apex d of the crest of one groove around the intersection with the optical axis 13. As will be described later, this forms the upper surface 11 of the groove of FIG. Similarly, a line connecting the outermost end a of the detection surface 2 and the apex c of the other mountain forming the groove is
A surface rotated about the intersection with the optical axis 13 is created. The groove formed by these surfaces is the groove 8 in FIG. The surface formed by the latter is the surface 9 below the groove 8. Hereinafter, similarly, eight grooves can be formed. It will be clear that the uppermost groove and the lowermost groove need only have one face.

Now, consider an arbitrary point P in the opening surface 7, an arbitrary point Q on the upper surface 11 and an arbitrary point R on the detector 2 as shown in FIG. In this case, since the line segment PQ has an intersection S with the inner wall of the cold shield 1, it passes through the point P and becomes a point Q.
The infrared rays incident in the direction are blocked by the inner wall of the cold shield 1. Therefore, infrared rays do not enter the detector 2 along the route from point P to point Q to point R. In addition, an arbitrary point p in the opening surface 7,
Consider an arbitrary point q on the lower surface 9 and an arbitrary point r on the detector 2. In this case, since the line segment qr has an intersection point t with the inner wall of the cold shield 1, the reflected / scattered light of infrared rays that passes through the point p and enters the point q is blocked by the inner wall of the cold shield 1 and does not reach the point r. Therefore, infrared rays do not enter the detector 2 along the route from point p to point q to point r. That is, when the intersection point of a straight line passing through an arbitrary point P in the cold shield opening surface 7 and the surface forming the groove of the inner wall of the cold shield 1 is Q and an arbitrary point on the detector 2 is R, the line is Point Q is the intersection of the segment PQ or line QR and the cold shield 1 inner wall
Other than that, the groove structure has one or more. Therefore, the reflected / scattered light of infrared rays that has entered the groove 8 having the above structure from the inside of the cold shield opening surface 7 does not directly enter the detector 2.

Therefore, the cold shield of this embodiment having the above groove structure has very little infrared reflected / scattered light on the inner wall of the cold shield 1 incident on the detector, and the shot noise generated in the detector 2 can be reduced. Further, since the baffle is unnecessary, the outer diameter of the cold shield 1 can be close to the diameter of the opening surface 7, and the cold shield and the cold head can be downsized, so that the heat load of the cooler can be reduced. Considering the case where there is a partial point Q at the top of the mountain in the above description, only the point Q intersects with the inner wall of the cold shield 1. That is, the infrared light incident on the point Q is reflected and scattered, and a part of the infrared light is incident on the detector 2. However, since the area of the mountain portion is sufficiently smaller than the area of the groove, the infrared rays incident on the detector 2 along the above path can be ignored.

Example 2. In Example 1, the cross section of the groove was a straight line, but as shown in the detail enlarged view of FIG. 2, the same effect is obtained if it is inside the surface connecting the peak and the valley.

Example 3. In the above embodiments, the intervals between the grooves in the direction between the opening surfaces are the same, but they may not be the same. Furthermore, in the above-mentioned embodiment, all the grooves have a structure in which they are blocked by incident light from an arbitrary point in the upper opening surface 7, but even if some of the grooves are out of this structure, If the structure of the above embodiment can be adopted as a whole, a practical shielding effect can be obtained.

Example 4. In this embodiment, a ring-shaped groove is formed on the inner wall of the cold shield in the first embodiment, whereas a spiral continuous thread groove is used. When a cold shield is created by machining, compared to engraving an annular groove in which each groove is separated, the continuous spiral shape greatly facilitates production.

Example 5. There may be a plurality of continuous spiral grooves. It should be noted that the same effect can be obtained by intersecting the screw-shaped grooves and carving them in a mesh shape.

Embodiment 6. FIG. 3 is a cross-sectional view showing another embodiment of the cold shield according to the present invention. In FIG. 3, the same reference numerals as those used in the previous drawings designate the same or corresponding parts. In FIG. 3, 3 is the cold shield of this embodiment.

FIG. 4 is a sectional view for comparing the dimensions of the conventional cold shield 4 and the cold shield 3 of this embodiment. Since the cold shield 3 of the present invention has a shape in which the inner wall spacing on the detector surface is narrower than the inner wall spacing near the opening surface, the cold shield 3 and the cold head 10 can be made smaller and the heat load of the cooler can be reduced. The baffle attached to the cold shield 3 has a smaller protruding amount in the optical axis direction than the conventional baffle except for the front baffle, and thus the number of sheets needs to be increased as compared with the conventional one. However, since the baffle size per sheet is smaller than that of the conventional one, the increase in the heat load caused by the increase in the number of sheets is smaller than that when the conventional baffle is added. Further, the increase in the heat load due to the increase in the number of baffles is sufficiently small as compared with the reduction amount in the heat load due to the downsizing of the cold shield 3 and the cold head 10. In addition, the inner dimension 16 is determined by a shape in contact with the truncated cone described in the first embodiment.

Example 7. FIG. 5 is a cross-sectional view showing another embodiment of the cold shield according to the present invention. In FIG. 5, the same reference numerals as those used in the previous drawings designate the same or corresponding parts. In FIG. 5, 19 is a cold shield of this embodiment. In this embodiment, the inner wall has grooves having the structure shown in the first embodiment.
In this case, as shown in FIG. 6, the baffle is not required, and the cold shield can be installed very close to the region through which the infrared rays 16 emitted from the target object pass. Therefore, the smallest cold shield can be realized, and the heat load of the cooler can be reduced. Further, as shown in Example 1, it is possible to reduce infrared rays reflected and scattered by the cold shield inner wall and incident on the detector.

Example 8. In the above-described embodiment, the detection surface is circular and the optical receiving lens is also circular, so that the effective incident light is incident in the shape of a truncated cone. In this embodiment, the detection surface may be square or rectangular. In this case, the light may be incident in the shape of a conical cone connecting the four corners of the detection surface and the maximum effective end of the light receiving lens. As described above, although the cold shield of the above-described embodiment is described as having a circular cross section perpendicular to the optical axis, the shape of the cross section is not limited to this and may be an ellipse, a rectangle, a polygon, or the like. Although the groove of the structure shown in the first embodiment is provided on the inner wall of the cold shield in the seventh embodiment, the groove structure is not limited to this. The cold shield of the above embodiment may be provided with both baffles and grooves.

In the above embodiment, the groove is provided inside the cold shield. However, not only the groove but also the cold shield inner wall can be provided with irregularities to enhance the infrared absorption effect. For example, by engraving a large number of hemispherical depressions on the inner wall of the cold shield, the same effect as that of the groove can be partially provided. The shape of the depression is not limited to a hemispherical shape, and a conical shape, a pyramid shape, or the like can also be used. Further, by attaching a conical projection, for example, to the inner wall of the cold shield, the same effect as that of the groove can be partially provided. The shape of the protrusions is not limited to the conical shape, but the pyramidal shape, the hemispherical shape, or the like can also be effective. Although the first, second, and fourth embodiments have a structure in which a groove is formed on the inner wall, the cold shield side surface may be made of a thin material and bent to form the groove.

[0027]

Since the present invention is constructed as described above, it has the following effects.
The groove engraved on the inner wall of the cold shield according to the specified rule reflects infrared rays from the inner wall of the cold shield that enters the detector.
Reduces scattered light and miniaturizes cold shields and cold heads. In addition, the cold shield, which has a narrow inner wall spacing on the infrared detector surface compared to the inner wall spacing near the opening surface, can reduce the size of the cold shield, reduce the noise generated by the detector, and reduce the heat load on the cooler. .

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating the groove shape of the inner wall of the cold shield according to the first and second embodiments of the present invention.

FIG. 3 is a sectional view showing Embodiment 6 of the present invention.

FIG. 4 is a cross-sectional view comparing the dimensions of a cold shield according to a sixth embodiment of the present invention and a conventional cold shield.

FIG. 5 is a sectional view showing Embodiment 7 of the present invention.

FIG. 6 is a sectional view showing a conventional infrared imaging device.

FIG. 7 is a cross-sectional view illustrating the effect of a baffle provided in a conventional cold shield.

FIG. 8 is a cross-sectional view illustrating an effect of a groove used in a lens barrel of an optical system.

FIG. 9 is a cross-sectional view illustrating a case where the effect of the groove provided on the inner wall of the cold shield cannot be sufficiently obtained.

[Explanation of symbols]

 1 Cold shield 2 Detector 3 Cold shield 6 Infrared rays incident from outside the field of view 7 Cold shield opening surface 8 Cold shield inner wall groove 9 Lower surface of groove 11 Upper surface of groove 8 13 Optical axis 16 From target object Infrared emitted 19 cold shield

Claims (5)

[Claims] 1. An arbitrary integer N provided outside a truncated cone surface connecting the maximum effective diameter end of the object-side opening surface of the cold shield and the maximum effective diameter end corresponding to the light receiving surface placed on the opposite side of the cold shield. For each of the ring-shaped vertices, a line formed by a line connecting the N effective peaks from the maximum effective diameter end of the object-side opening surface and a line connecting the maximum effective diameter ends of the light receiving surface to the respective vertices are formed. A cold shield for shielding light rays or infrared rays, which is provided with a groove formed by the surface to be formed. 2. The groove is a surface inside a surface formed by a line connecting N apexes from the maximum effective diameter end of the object-side opening surface and a line connecting the apex from the maximum effective diameter end of the light receiving surface. The cold shield according to claim 1, wherein the cold shield is formed by a surface located inside of a surface formed by. 3. The groove is one or a plurality of spiral grooves continuously formed from a part of the object side opening surface toward the learning surface side opening surface. Item 1
The cold shield according to claim 2 or 3. 4. A cone-shaped surface equivalent to the maximum effective diameter end of the light-receiving lens and a maximum effective diameter end equivalent to the light-receiving surface is set, and a plurality of concentric baffles having outer edges are provided outside the cone-shaped surface equivalent. The plurality of baffles are cold shields for shielding light rays or infrared rays in which the diameter of the baffle on the light receiving surface side is smaller than the diameter of the baffle on the lens surface side. 5. The equivalent of a truncated cone surface connecting the maximum effective diameter end of the light receiving lens and the maximum effective diameter end corresponding to the light receiving surface is set, and the cold shield is equivalent to the diameter on the light receiving surface side rather than the diameter on the lens surface side. The cold shield according to claim 1 or 2, wherein the cold shield is made smaller.