Reflective Triplet Optical Form with External Rear Aperture Stop
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Solution Overview
Problem
Modern reflective optical triplets with aperture stops on the optical axis restrict the field of view and power distribution, leading to radiation occlusion and decreased image quality, especially in infrared imaging applications where refractive elements are not optimal due to absorption and manufacturing challenges.
Innovation Solution
A reflective triplet optical form with an external rear aperture stop is configured between the last optical element and the image plane, providing effective cold shielding and reducing radiation reflection and scattering, thereby enhancing image quality by placing the aperture stop between the tertiary mirror and the image plane within a cryo-vac cold cavity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the aperture stop is placed on the optical axis in prior art reflective triplets, then the optical system can be compactly arranged, but the field of view is restricted and radiation occlusion occurs
Solution Approach 1:
The aperture stop is relocated from the optical axis to an external position in the paraxial region, changing its spatial dimensionality relative to the optical path. This dimensional repositioning allows the stop to define the aperture without blocking off-axis rays, thereby expanding the field of view while maintaining a compact optical arrangement.
2Reliability
If refractive optical elements are used to control aberrations, then aberration correction is effective, but radiation absorption increases and manufacturing becomes difficult for large apertures
Solution Approach 1:
The patent replaces refractive optical elements with reflective optical elements (mirrors) to correct aberrations. The reflective triplet configuration uses precisely figured mirror surfaces to control spherical aberration, coma, and astigmatism without the radiation absorption inherent in refractive materials, thereby maintaining aberration correction effectiveness while reducing energy loss.
3Reliability
If the aperture stop is positioned on the secondary mirror in prior art, then the optical path is simplified, but cold shielding effectiveness is reduced leading to increased noise in infrared imaging
Solution Approach 1:
The aperture stop is extracted from its traditional position on the secondary mirror and relocated to an external position in the paraxial region between the tertiary mirror and the focal plane. This extraction allows the stop to be positioned optimally for defining the aperture while enabling effective cold shielding of the focal plane, thereby reducing thermal radiation noise and improving infrared image quality.
Solution Approach 2:
The externally positioned aperture stop acts as an intermediary element that mediates between the optical path and the focal plane. By positioning the stop in the paraxial region, it effectively blocks thermal radiation paths to the focal plane while maintaining proper aperture definition, thus reducing noise without compromising optical performance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration allows for higher quality infrared images with reduced noise and increased field of view, achieving image quality comparable to refractive systems at larger apertures while maintaining the advantages of all-reflecting systems, such as reduced weight and accuracy across various wavelengths.
Implementation Method 1
radiation enters the system from a distant object, is received on a primary mirror, is reflected onto a secondary mirror, is received on a tertiary mirror, and finally, is focused on an image plane
Implementation Method 2
With the aperture stop in this position, the image plane may be cold shielded more effectively than prior art systems. Therefore, it is possible to generate higher quality infrared images due to a decrease in radiation reflected and/or scattered from the optical elements and the structure within the optical system
Data Source
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AI summary
An all-reflecting, non-relayed optical system having an aperture stop and an optical axis and configured to provide images of objects. The system includes a positive power primary mirror configured to receive radiation from the objects, a negative power secondary mirror configured to receive the radiation reflected from the primary mirror and a positive power tertiary mirror configured to receive the radiation reflected from the secondary mirror. The system further includes a focal plane configured to receive the radiation reflected from the tertiary mirror and to form an image of the objects. The aperture stop of the optical system is located between the tertiary mirror and the image plane. Accordingly, the image plane may be cold shielded to prevent or reduce radiation reflected from the optical elements that interferes with the desired image.