Optical system for wide angle IR imager
First Claim
1. In an IR sensor head containing an IR detector array installed within a cryogenic enclosure, said sensor head exhibiting a wide field of view, high optical performance and high cold shielding efficiency, the combination comprising:
- (A) a first objective lens having a focal length (f1) installed on said optical axis for imaging the object field into a primary image plane,(B) an evacuated cryogenic, cold shielding enclosure, including(1) an aperture in the cold shield installed on said optical axis for admission of IR image radiation and for stopping unfocused IR background illumination, and(2) cooling means(C) an IR detector array installed in said enclosure on said optical axis and cooled by said cooling means, and(D) a telecentric lens arrangement comprising(1) a second lens having a focal length (f2) installed outside said enclosure on said optical axis at a distance from said primary image plane for collimating the ray bundles of said primary image points,(2) a third lens having a focal length (f3) installed within said enclosure on said optical axis at a distance from said IR detector array for focusing said collimated ray bundles of said image points into a secondary image plane on said IR detector array,said cold shield aperture being spaced between said second and third lenses, and of minimum size for intercepting said collimated ray bundles for maximum aperture efficiency,said arrangement permitting correction of inaccuracy in the positioning of said third lens in relation to said IR detector array by a compensatory repositioning of said objective lens in relation to said telecentric lens arrangement without a significant loss in optical performance.
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Accused Products
Abstract
The invention relates to a high performance optical system for a wide angle IR imager requiring a cryogenic environment for the IR detector array. The wide angle requirement makes it necessary for one lens to be behind a "cold aperture" within the cryogenic environment where focusing is difficult and performance of the aperture reduced. These objectives are minimized by use of a telecentric lens pair, one member of which is within the cryogenic environment. The telecentric lens pair refocuses the primary image formed by an objective lens, permitting a high quality image to be formed on the IR detector array. The usual errors in positioning the internal lens, which might impair the quality of the focused image, are avoided by a compensatory repositioning of the externally accessible objective lens. The use of collimated bundles of light, characteristic of telecentric lens pairs, permits maximum aperture efficiency, and also provides a fourier transformation plane in which spatial filtering may be used to reduce IR background of low spatial frequency.
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Citations
6 Claims
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1. In an IR sensor head containing an IR detector array installed within a cryogenic enclosure, said sensor head exhibiting a wide field of view, high optical performance and high cold shielding efficiency, the combination comprising:
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(A) a first objective lens having a focal length (f1) installed on said optical axis for imaging the object field into a primary image plane, (B) an evacuated cryogenic, cold shielding enclosure, including (1) an aperture in the cold shield installed on said optical axis for admission of IR image radiation and for stopping unfocused IR background illumination, and (2) cooling means (C) an IR detector array installed in said enclosure on said optical axis and cooled by said cooling means, and (D) a telecentric lens arrangement comprising (1) a second lens having a focal length (f2) installed outside said enclosure on said optical axis at a distance from said primary image plane for collimating the ray bundles of said primary image points, (2) a third lens having a focal length (f3) installed within said enclosure on said optical axis at a distance from said IR detector array for focusing said collimated ray bundles of said image points into a secondary image plane on said IR detector array, said cold shield aperture being spaced between said second and third lenses, and of minimum size for intercepting said collimated ray bundles for maximum aperture efficiency, said arrangement permitting correction of inaccuracy in the positioning of said third lens in relation to said IR detector array by a compensatory repositioning of said objective lens in relation to said telecentric lens arrangement without a significant loss in optical performance. - View Dependent Claims (2, 3, 4, 5, 6)
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Specification