JP2691226B2 - Infrared imaging optics - Google Patents

Description

TECHNICAL FIELD The present invention relates to an infrared imaging optical device.

[Prior Art] A conventional device of this type has a structure as shown in FIG. In the figure, the image of the imaging target formed on the intermediate image forming surface by the objective lens 102 is formed on the light receiving surface of the infrared detector 104 by the relay lens 103. In general, photoelectric devices for infrared rays have a narrow forbidden band and dark current easily flows.
The detector 104 is surrounded by a cold shield 105 which has an opening for passing an effective light flux from the relay lens 103 and shields radiation (thermal radiation) from surrounding objects.
It has been cooled to a temperature of approximately 0K. In the infrared imaging optical device having such a configuration, the detector 10 is provided from an object other than the imaging target without blocking the optical path of the light flux from the relay lens 103.
Cold shield 1 to reduce thermal radiation incident on 4
05 It has been proposed to match the aperture with the exit pupil of the imaging optics.

[Problems to be Solved by the Invention] However, the above-described conventional techniques have the following problems.

First, since the height of the cold shield opening from the light receiving surface of the detector must correspond to the position of the exit pupil,
There is a problem that the cold shield cannot be downsized and the cooling load cannot be reduced. Especially when many photoelectric elements of the detector are arranged in two dimensions and the light receiving area is large, the distance between the exit pupil and the image forming surface (light receiving surface) becomes long, so the cold shield becomes larger and cools accordingly. The load will be large.

Further, since the size of the opening of the cold shield is fixed, changing the size of the aperture stop of the imaging optical system causes a problem that the exit pupil and the size of the cold shield opening do not match. . That is, when the aperture stop is narrowed, the size of the exit pupil is smaller than that of the cold shield opening, and thermal radiation from an object other than the imaging target is incident on the detector, which lowers the sensitivity of the detector.

Furthermore, the sensitivity of infrared detectors is impaired if water condenses on the light-receiving surface. Therefore, in general, the optical window member surrounds the detector (outside the cold shield) so that the detector light-receiving part can be kept in vacuum. In many cases, the vacuum layer needs to be made thick to some extent from the viewpoint of the heat insulating effect, and there is a problem that the apparatus becomes larger.

In addition, as described above, the position and shape of the cold shield opening must be fixed, so if the magnification of the objective lens is changed, the exit pupil and cold shield opening will not match, and the detector There is also a problem that the sensitivity of is reduced.

The invention of the present application has been made in view of the above problems, and the first invention (Claim 1) can improve the cooling efficiency of the detector, and the opening of the detector can be performed without lowering the sensitivity of the detector. An object is to provide an infrared imaging optical device capable of changing the size of a diaphragm.

A second aspect of the present invention (claim 3) is to provide an infrared imaging optical device capable of reducing the size of the device without lowering the sensitivity of the detector.

Further, the third invention (claim 4) is intended to provide an infrared imaging optical device capable of maintaining high cooling efficiency and sensitivity even when the magnification of the objective lens is changed.

[Means for Solving the Problems] In the infrared imaging optical device of the first invention, an imaging optical system having an objective lens and a relay lens and a light receiving surface are aligned with a position of a final image forming surface of the imaging optical system. And an infrared detector disposed in, and a cold shield that is arranged so as to surround the detector with an opening through which the light flux from the imaging optical system passes and that shields thermal radiation from the surroundings of the detector. In order to achieve the above-mentioned object, the infrared imaging optical device comprises an opening of the cold shield that matches an exit pupil of the imaging optical system or a position conjugate with the exit pupil, and the opening of the imaging optical system. The infrared imaging optical device is characterized in that the image-side surface of the diaphragm is a mirror surface.

An infrared imaging optical device according to a second aspect of the present invention includes an imaging optical system having an objective lens and a relay lens, and an infrared detector arranged so that a light receiving surface thereof coincides with a position of a final image forming surface of the imaging optical system. An optical window member for sealing the periphery of the detector,
An infrared imaging optical device having a support member for supporting the optical window member, wherein the optical window member is aligned with an exit pupil of the imaging optical system or a position conjugate with the exit pupil of the imaging optical system in order to achieve the above-mentioned object. In the infrared imaging optical device, the detector-side surface of the support member is a mirror surface.

An image pickup optical device according to a third aspect of the present invention includes an image pickup optical system having an objective lens and a relay lens, an infrared detector arranged so that a light receiving surface thereof coincides with a position of a final image forming surface of the image pickup optical system, An infrared imaging optical device comprising: a cold shield that has an opening through which a light flux from an imaging optical system passes and surrounds the detector, and that shields thermal radiation from the periphery of the detector. In order to achieve the above-mentioned object, even when the imaging optical system zooms the objective lens, the zooming optics whose exit pupil or a position conjugate with the exit pupil always matches the opening of the cold shield. It is an infrared imaging optical device characterized by comprising a system.

In the present specification, "the exit pupil and the cold shield opening (or the optical window member) are matched" means "the exit pupil and the opening (or the optical window member) are in the same position and have the same size". This is also referred to as “aperture matching” hereinafter.

[Operation] In the first invention, the exit pupil and the opening of the cold shield are matched (generally, the position and size of the exit pupil can be set to desired values in optical design,
The cold shield opening can be matched with the exit pupil of the entire optical system by designing the objective lens), and the image-side surface of the aperture stop is a mirror surface, so radiation from the cold shield opening forming surface The light is specularly reflected by the mirror surface of the aperture stop and returns to the cold shield aperture forming surface. The heat radiation that enters the cold shield and the detector from surrounding ambient temperature objects is significantly reduced, and the radiant light of the cooled cold shield and the detector itself enters (narcissus phenomenon), so the cooling load is reduced. Will be reduced.

If the aperture stop is stopped while the exit pupil is aligned with the cold shield aperture, the size of the exit pupil will be smaller than the aperture, but even in that case, the radiation that enters the detector from outside the imaging target is cooled. Detector (and supporting substrate)
Since the light is emitted from itself, it is substantially equivalent to the cold shield opening being narrowed.

In the second invention, the optical window member is arranged at a position that matches the exit pupil, and the cold shield is arranged inside this optical window member. That is, although the cold shield opening does not match the exit pupil, the detector side surface of the support member of the optical window member is configured as a mirror surface,
In addition to the effective luminous flux from the relay lens, only the emitted light from the cooled cold shield enters the detector. That is, the cold shield and the optical window member can be made smaller than before without lowering the sensitivity of the detector.

Further, in the third invention, when the magnification of the objective lens is changed, the position and size of the exit pupil are changed accordingly. However, the position and size of the aperture stop should be adjusted so as to satisfy the conditions described later. Therefore, aperture matching can be realized even after zooming.

[Embodiment] FIG. 1 is an optical path diagram showing an embodiment of the first invention. The optical system of such an imaging optical device has the objective lens 2 and the image formed on the intermediate image forming surface by the objective lens 2 on the light receiving surface of the infrared detector 4 (the area from point A'to point A "in the figure). The relay lens 3 for forming an image is provided, and the detector 4 is the relay lens 3
It is surrounded by a cold shield 5 that has an opening for passing an effective light flux from the same and shields heat radiation from surrounding objects, and is cooled to a temperature of about 80K. The aperture stop 1 of the imaging optical system and the aperture of the cold shield 5 have a conjugate relationship (that is, the exit pupil and the aperture match), and the surface of the aperture stop 1 on the detector 4 side is a mirror surface. There is.

In the imaging optical device having such a configuration, all the light emitted from the end point A of the opening of the cold shield 5 within the angle α (light emitted from the light receiving surface points A ′ to A ″ of the detector 4) is the aperture stop 1. The light is specularly reflected at the end point B of the opening and returns to the point A. Similarly, all the emitted light from the opening forming surface (the height h from the light receiving surface) of the cold shield 5 returns to the cold shield 5. That is, with the configuration shown in FIG. 1, the cooled radiation of the detector 4 and the cold shield 5 itself is reflected by the mirror surface of the aperture stop 1 and enters the detector 4 and the cold shield 5. As a result, the thermal radiation incident on the detector from the surrounding room temperature object is reduced, so that the specific detection sensitivity of the detector 4 D ^* (D ^* = A ^1/2 (Δf)
^1/2 / (NPE) [cm ・ Hz ^1/2・^-1 ]; where NEP is the noise equivalent power = JA ・ (S / N) [W], J is the energy per unit area of the incident light flux [W / cm ² ], S is signal output voltage [V], N is noise voltage [V], A is element effective area [cm ² ], Δf is infrared bandwidth to be measured [Hz]) .

Further, in this embodiment, since the field stop 6 is provided on the intermediate image forming surface and the surface of the field stop 6 on the detector side is also configured as a mirror surface,
The end point C (A ″) of the non-light-receiving surface of the detector 4 and the end point D of the aperture of the field stop 6 also have a conjugate relationship, and the light emitted from the point C is also reflected by the mirror surface of the field stop 6 and returns to the point C. become.
That is, since the emitted light from the non-light receiving surface of the detector 4 also returns to the detector 4 (non-light receiving surface), the cooling efficiency can be improved. At this time, if the imaging optical system is a telecentric system, the emitted light from the detector 4 will be more efficiently reflected by the mirror surfaces of the aperture stop 1 and the field stop 6.

Next, FIG. 2 is an optical path diagram showing another embodiment of the first invention. The image pickup optical device of the present embodiment has the first basic configuration.
Similar to the embodiment shown in the figure, a field stop is not provided on the intermediate image plane, and the size of the aperture of the aperture stop 21 is variable. In such an imaging optical device, when the aperture stop 21 is narrowed down as shown in the figure, the size of the exit pupil becomes the size shown by points E to F in the figure. At this time, the size of the exit pupil is smaller than the size of the opening of the cold shield 5, but the light fluxes within the angles γ and γ ′ are reflected by the mirror surface of the aperture stop 21 and pass through the same optical path to the detector 4 Return to the point on the optical axis of the light receiving surface.

A light beam emitted from the end point E of the exit pupil within the angle β (a light beam emitted from the point E ′ to the point E ″ including the light receiving surface of the detector, the periphery and the non-light receiving portion) is the end point B of the aperture stop 21. The light is reflected by ′ and returns to the points E ′ to E ″ of the detector 4 as it is. Similarly, the end point A of the opening of the cold shield 5 is also reflected by the mirror surface of the aperture stop 21 and returns to the area of points A ′ to A ″.

That is, with the configuration as shown in FIG. 2, even if the exit pupil is smaller than the size of the opening of the cold shield 5 by narrowing the aperture stop 21, the light is not incident on the detector 4 from other than the imaging target. Since the emitted light is from the cooled detector 4 and the cold shield 5 itself, it is substantially equivalent to the aperture of the cold shield 5 being narrowed.

Next, an embodiment of the second invention will be described with reference to FIG. The optical system of the image pickup optical device according to the present embodiment is an objective lens.
32 and a relay lens 33 for forming an image formed on the intermediate image forming surface 32a by the objective lens 32 on the light receiving surface of the infrared detector 34, and the detector 34 is an effective light beam from the relay lens 33. It is cooled to a temperature of about 80K by being surrounded by a cold shield 35 that has an opening for passing through and shields heat radiation from surrounding objects. The outside of the cold shield 35 is sealed by an optical window member 7a that transmits infrared rays and a support member 7b for this window member, and the detector 34 is placed in a vacuum.

The surface of the support member 7b on the detector 34 side is a mirror surface, and the end portion of the optical window member 7a (the connection portion with the support member 7b) is tapered in terms of pressure resistance. And
The surface of the optical window member 7a on the detector 34 side and the aperture stop of the imaging optical system.
31 has a conjugate relationship (that is, the exit pupil and the optical window member 7a match). The height of the aperture forming surface of the cold shield 35, which is arranged in a vacuum together with the detector 34, is lower than the position of the exit pupil, and the aperture diameter does not block the optical path of the effective light beam from the relay lens 33. Is larger than the exit pupil. In addition, in this embodiment, the outer surface of the cold shield 35 is formed of a black body (reflectance zero, emissivity 100%).

In the cross section including the optical axis of the imaging optical device having such a configuration, the light is incident on the point G from within the angle δ defined by the light receiving point G on the optical axis, the exit pupil end point H, and the cold shield 35 opening end point I. The generated heat radiation is emitted from the detector 34 light receiving part and the cold shield 35 which are all cooled by the cooler (not shown). For example, the emitted light from the point J on the outer surface of the cold shield 35 is reflected by the mirror surface of the optical window member 7a and enters the point G on the light receiving surface of the detector 34 as shown in the figure.
Further, regarding the end point K of the light receiving portion, a similar situation is established for thermal radiation that enters from the angle ε defined by the three points H, K, and I, and the radiation light from the cold shield 35 enters. The same applies to a cross section that does not include the optical axis. Therefore, the F value (F = f / D; defined by the optical window member 7a).
f is the focal length of the optical system, D is the diameter of the entrance pupil, and the F value defined by the cold shield 35 substantially matches.

That is, in the imaging optical system shown in FIG. 3, the supporting portion 7b of the optical window member 7a arranged so as to match the exit pupil.
Since the surface of the detector on the detector side is configured as a mirror surface, the inner surface (mirror surface) of the support portion 7b functions as a substitute for the cold shield arranged so that the exit pupil and the opening match. It becomes cold shield 35 in comparison with conventional
Also, the optical window member 7a and the supporting member 7b can be downsized, and the cooling load can be reduced accordingly. Further, the downsizing of the optical window member 7a and its supporting member 7b is also advantageous in terms of mechanical strength (pressure resistance).

The outer surface of the cold shield 35 is preferably formed of a black body as in this embodiment in order to make the radiated light of the cooled cold shield 35 itself incident on the detector 34, but the outer surface of the cold shield 35 is The emissivity and reflectance are not particularly limited. Cold shield 35
When the outer surface is a mirror surface, the supporting substrate 8 of the detector 34
(In FIG. 3, the substrate 8 is arranged in the cold shield 35, but the bottom of the supporting member 7a may be closed by the substrate 8). Also, the light is reflected by the mirror surface of the support member 7b and enters the detector 34.

Further, although the detector 34 and the cold shield 35 are arranged in a vacuum in the above-mentioned embodiment, it goes without saying that the same can be applied to the case where an inert gas or the like is sealed.

Further, in the embodiment shown in FIG. 3, the inner surface (detector side) of the optical window member 7a is matched with the exit pupil, but the outer surface is matched with the exit pupil, and the outside of the optical window member 7a is matched. By arranging a diaphragm whose surface on the detector 34 side is a mirror surface at the surface position, the F value of the optical system can be changed by this diaphragm without lowering the sensitivity of the detector as in the embodiment described in FIG. Can be changed.

Next, an embodiment of the third invention will be described with reference to FIGS. 4 and 5.

First, the conditions for matching the exit pupil and the cold shield opening will be described with reference to FIG. The structure of the image pickup optical device shown in FIG. 4 is basically the same as the structure of the embodiment shown in FIG. In the figure, assuming that the objective lens 2 is a single lens, the distance from the principal point to the aperture stop 1 is s,
The focal length of the objective lens 2 is f ₁ , the distance from the principal point of the relay lens 3 to the intermediate image plane is a, the distance to the final image plane (light receiving surface of the detector 4) is b, and the focal length of the relay lens 3 is Let f _{2 be} the height of the opening of the cold shield 5, h be the exit pupil position (distance from the relay lens principal point) be x, the exit pupil diameter be φ, and the aperture stop diameter be D.

Then, if the position conjugate with the entrance pupil is x ′ and the diameter of the entrance pupil is D ′, then in the optical axis direction x = b−h (4) holds, and D ′ = Dx ′ / s (5) φ = D′ x / (f ₁ + a−x ′) (6) holds in the direction perpendicular to the optical axis.

Solving (1) to (4), s = f ₁ + [(b−f ₂ ) {h− (b−f ₂ )} / (hf ₂ ² )] f
₁ ² (7) Further solving (5) and (6) gives f ₁ / D = (h / φ) × f ₂ / b−f ₂ = (h−φ) × (a / b)
(8) Therefore, when the relay lens 3 is fixed and the angle of view is changed by exchanging the objective lens 2, the aperture stop 1 is placed at the position determined by the equation (7) and determined by the equation (8). If the size of the aperture to be set is set (that is, if a constant F value is determined), the exit pupil and the cold shield 5 aperture always match.

FIG. 5 is an optical path diagram showing a case where the focal length of the objective lens is changed in the image pickup optical apparatus of FIG.

At this time, the distance l from the intermediate image plane of the aperture stop 51 is l = s ′ + f ₁ ′ = [(b−f ₂ ) {(h− (b−f ₂ )} / (hf ₂ ² )] f ₁ ²
+ 2f ₁ (9) is obtained, and in the equation (9), if f ₁ is rewritten as t and F (t), then F (t) = pt ² + 2t = p (t + 1 / p) ² −1 / p (10 ) _{where, p = (b-f 2} ) a _{{h- (b-f 2)} } / (hf 2).

Therefore, the aperture stop 51 when the magnification of the objective lens is changed
The condition for making the amount of movement of F to be a value proportional to the focal length of the objective lens 52 is F ″ (t) = 0, that is, p = 0 is solved, and h = b−f ₂ (s = f ₁ ) ( 11)

That is, if the position of the aperture stop 51 is aligned with the front focus position of the objective lens 52 and the objective lens 52 is telecentric on the exit side, the exit pupil can be aligned with the opening of the cold shield 5.

In addition, the magnification of the objective lens is changed in two steps (t = f ₃ ,
f ₄ ) If F is satisfied, F (f ₃ ) = F (f ₄ ) = 2f ₃ f ₄ / (f ₃ + f ₄ ) holds, and the exit pupil positions become equal even if the magnification is changed.

Then, solving equation (12) for h gives h = (b−f ₂ ) ² / {(b−f ₂ ) + f ₂ ² / f ′ (13).

That is, by arranging the cold shield 5 opening at this position, the exit pupil and the cold shield opening can be matched only by changing the size of the entrance pupil when the magnification is changed in two steps.

Further, this condition is also the case where the amount of change in the aperture stop position F (t) when the focal length of the objective lens is continuously changed from f _{3 to} f ₄ is the minimum. Further, when the positions of the entrance pupils from the principal point of the objective lens are made equal at the time of the two-step magnification change, F (t) =
The same applies to pt ² + t.

In the above description, the exit pupil and the cold shield opening are made to match, but it goes without saying that the above-described conditions are also applied when the exit pupil and the optical window member are made to match. . Further, although the objective lens is a single lens in the above description, there are similar solutions for aperture matching for multi-stage lenses such as two-stage lenses and three-stage lenses.

Further, when the focusing mirror 9 is inserted into the intermediate image plane as shown in FIG. 6 in the image pickup optical apparatus having the configuration shown in FIG. 4, if the mask portion 10 of the focusing mirror 9 is configured as a mirror surface,
A focusing mirror can be obtained by utilizing the narcissus phenomenon (the light emitted from the detector is reflected by the mirror surface of the mask portion 10 and returned to the detector). Further, when it becomes a problem that the reflected light other than the mirror surface (mask portion 10) is incident on the detector, as shown in FIG. 7, two wedge-shaped members are bonded together to form the plane parallel plate 11. The focusing mirror 9 is formed on the bonding surface, and the focusing mirror 9 is formed.
The parallel plane plate 11 may be inserted with an inclination with respect to the optical axis AX so that is positioned at the intermediate image plane. By doing so, it is possible to prevent reflected light other than the mask 10 from entering the detector.

Further, as shown in FIG. 8, if the plane-parallel plate 12 is inserted while being inclined with respect to the optical axis AX and the plane-parallel plate 12 is rotated about the optical axis as a rotation axis, the pixel of the detector is equivalently Although the number or the size of one pixel can be increased, the aberration of the optical system can be minimized by disposing the plane-parallel plate 12 at the position of the intermediate image plane 2a.

[Effects of the Invention] As described above, in the first invention, the exit pupil and the cold shield aperture are aligned, and the image side of the aperture stop is configured as a mirror surface. It is possible to change the size of the cold shield opening. Therefore, it is possible to increase the F value of the optical system by narrowing the aperture stop and to match the F value defined by the cold shield with the F value of the optical system to enhance the sensitivity (D *) of the detector.

Further, in the second invention, since the exit pupil and the optical window member are coincident with each other and the supporting portion of the optical window member is constituted by the mirror surface, the detector is arranged around the detector without lowering the sensitivity of the detector. The size of the optical window member and its supporting member and the cold shield can be made smaller than the conventional size.

Further, in the third aspect, the exit pupil and the cold shield aperture are always matched even when the magnification of the objective lens is changed, so that the angle of view can be changed while maintaining cooling efficiency and detection sensitivity.

[Brief description of the drawings]

1 is an optical path diagram for explaining an embodiment of the first invention, FIG. 2 is an optical path diagram for explaining another embodiment of the first invention,
FIG. 3 is an optical path diagram for explaining an embodiment of the second invention, FIGS. 4 and 5 are optical path diagrams for explaining the third invention, and FIGS. 6 and 7 are examples of insertion of a focusing mirror. Optical path diagram to explain, No. 8
FIG. 9 is an optical path diagram for explaining an insertion example of a plane parallel plate, and FIG. 9 is an optical path diagram for explaining a conventional example. [Explanation of symbols for main parts] 1.21,31 …… Aperture stop 2,32 …… Objective lens 3,33 …… Relay lens 4,34 …… Detector 5,35 …… Cold shield 6 …… Field stop 7a… … Optical window member 7b …… Supporting member

Claims (5)

(57) [Claims] 1. An image pickup optical system having an objective lens and a relay lens, an infrared detector arranged such that a light receiving surface thereof coincides with a position of a final image forming surface of the image pickup optical system, and an image pickup optical system from the image pickup optical system. In an infrared imaging device that is arranged to surround the detector with an opening through which a light beam passes, and a cold shield that shields thermal radiation from the periphery of the detector, wherein the opening of the cold shield is the An infrared imaging optical device, characterized in that it is aligned with the exit pupil of the imaging optical system or a position conjugate with the exit pupil, and the image-side surface of the aperture stop of the imaging optical system is a mirror surface. 2. A field stop disposed on an intermediate image plane on which an image is formed by said objective lens, and an image side surface of said field stop is a mirror surface. Item 1
Infrared imaging optical device described. 3. An image pickup optical system having an objective lens and a relay lens, an infrared detector arranged so that a light receiving surface thereof coincides with a position of a final image forming surface of the image pickup optical system, and a periphery of the detector. In an infrared imaging optical device having an optical window member for sealing and a support member for supporting the optical window member, the optical window member is aligned with an exit pupil of the imaging optical system or a position conjugate with the exit pupil, and the support is provided. An infrared imaging optical device characterized in that the surface of the member on the detector side is configured as a mirror surface. 4. An image pickup optical system having an objective lens and a relay lens, an infrared detector arranged so that a light receiving surface thereof coincides with a position of a final image forming surface of the image pickup optical system, and an image pickup optical system from the image pickup optical system. In an infrared imaging optical device having a cold shield that has an opening through which a light flux passes and that surrounds the detector, and that shields thermal radiation from around the detector, the imaging optical system includes: An infrared imaging optical device characterized in that, even when the objective lens is zoomed, the exit pupil or a position conjugate with the exit pupil is a zooming optical system which always matches the aperture of the cold shield. 5. The infrared imaging optical device according to claim 4, wherein the objective lens is telecentric.