Cold-shielded Infrared Spectrometer Retro-reflection Design
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Solution Overview
Problem
Conventional dispersive infrared spectrometers face challenges with thermal noise due to the need for a large cryogenic dewar to house multiple optical components, leading to increased heat load, longer cooling times, and optical misalignment issues.
Innovation Solution
Only the detector is housed within a cold dewar, with the remaining optical components at ambient temperature, utilizing telecentric flat-field foreoptics, a dispersive element, and a flat-field relayed imager to retro-reflect in-band wavelengths back into the dewar, minimizing thermal noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If multiple optical components are housed within a cryogenic dewar to reduce thermal noise, then thermal noise is reduced, but the dewar size increases, heat load increases, cooling time increases, and optical misalignment risk increases
Solution Approach 1:
The patent extracts only the essential component (detector) into the cryogenic dewar, leaving non-essential optical components (optical bench, mirrors, lenses, dispersive element) outside at ambient temperature. This selective extraction reduces dewar volume while maintaining thermal noise reduction through the retro-reflection design that directs thermal radiation away from the detector
Solution Approach 2:
The patent converts the potentially harmful thermal radiation from ambient-temperature optical components into a beneficial configuration by using the retro-reflection design. The reflective substrate directs thermal radiation back toward the source rather than allowing it to reach the detector, thus converting what would be harmful thermal noise into a controlled optical path that maintains performance
2Object-affected harmful factors
If multiple optical components are housed within a cryogenic dewar to reduce thermal noise, then thermal noise is reduced, but heat load on refrigeration unit increases
Solution Approach 1:
The patent removes non-essential optical components from the cryogenic environment, extracting only the detector into the dewar. This dramatically reduces the mass requiring cooling and thus the heat load on the refrigeration unit, while the retro-reflection design ensures thermal noise from ambient components does not degrade performance
Solution Approach 2:
The patent changes the thermal state parameter of optical components from cryogenic to ambient temperature. By operating optical components at ambient temperature rather than cryogenic temperatures, the heat load on the refrigeration system is reduced while performance is maintained through the retro-reflection optical design
3Object-affected harmful factors
If multiple optical components are housed within a cryogenic dewar to reduce thermal noise, then thermal noise is reduced, but cooling time increases
Solution Approach 1:
The patent extracts non-essential optical components from the cryogenic dewar, leaving only the small detector inside. This reduces the total thermal mass that must be cooled, thereby reducing the time required to reach operating temperature while maintaining thermal noise reduction through the retro-reflection design
4Object-affected harmful factors
If multiple optical components are housed within a cryogenic dewar to reduce thermal noise, then thermal noise is reduced, but optical misalignment risk increases due to temperature differences
Solution Approach 1:
The patent removes optical components from the cryogenic environment, eliminating them from the thermal stress field. By keeping optical components at ambient temperature while only cooling the detector, the patent eliminates differential thermal expansion and contraction that would cause misalignment, thus improving reliability
Solution Approach 2:
The patent applies different thermal conditions to different parts of the system: the detector is kept cryogenic for low thermal noise, while optical components are kept at ambient temperature for stability. This localized quality approach allows each component to operate in its optimal thermal environment without compromising overall system 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 reduces thermal noise significantly, allowing for a smaller, less expensive cryogenic dewar and avoiding the need to cool bulky optical components, while maintaining spectrometer performance.
Implementation Method 1
utilizing telecentric flat-field foreoptics, a dispersive element, and a flat-field relayed imager to retro-reflect in-band wavelengths back into the dewar
Implementation Method 2
a substrate defining at least one slit, the substrate having a first reflective surface
Implementation Method 3
a telecentric flat-field collimator positioned facing the first reflective surface of the substrate and configured to collimate the light rays from the at least one slit to provide collimated light rays
Implementation Method 4
a dispersive element optically coupled to the telecentric flat-field collimator, the telecentric flat-field collimator being positioned between the substrate and the dispersive element, the dispersive element configured to receive and spectrally disperse the collimated light rays
Implementation Method 5
a flat-field relayed imager positioned between the dispersive element and the detector and configured to receive the dispersed light from the dispersive element and to image the dispersed light onto the detector
Implementation Method 6
a detector housed within a cryogenic dewar
Implementation Method 7
Only the detector is housed within a cold dewar, with the remaining optical components at ambient temperature
Data Source
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AI summary
A dispersive infrared spectrometer in which only a minimum number of optical components, for example, the detector (160) sub-system only, are housed within a cold/cryogenic dewar and the remaining optical components are at ambient temperature during operation of the spectrometer. In one example, the spectrometer includes a slit substrate (120) with a highly reflective surface, and the optical components of the spectrometer are configured and arranged such that for all in-band wavelengths, substantially all off-slit optical paths in the detector (160) field of view are retro-reflected off the reflective surface of the slit substrate (120) into the cryogenic dewar.