Cold Stage Actuation of Optical Elements in Cryogenic Dewars
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Solution Overview
Problem
Spectral imaging systems using circular blazed grating diffractive lenslet arrays face challenges in cooling infrared detectors while maintaining the close proximity of diffractive optical elements to the detector array, which is essential for effective infrared wavelength detection.
Innovation Solution
A cold stage actuation system with an adapter ring, resilient cold shield, and insulating translation arm allows for the mechanical actuation and cooling of lenslet arrays within a cryogenic dewar, utilizing high thermal conductivity materials and a low-power motor to minimize heat interference and maintain optical alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the infrared detector is placed inside a cryogenic dewar for cooling, then the detector temperature is reduced to improve infrared wavelength detection, but the diffractive optical elements cannot be placed close enough to the detector array
Solution Approach 1:
The system is divided into two thermal zones: a cold stage inside the dewar containing the detector array and optical elements, and a warm exterior containing the motor. The cold stage is segmented from the warm motor housing by thermal insulation barriers, allowing the optical elements to be cooled while the motor remains at ambient temperature.
Solution Approach 2:
A motor-driven translation stage acts as an intermediary mechanism between the warm motor and the cold optical elements. The motor extends a translation stage through the dewar wall, allowing mechanical actuation of the optical elements without direct thermal coupling between the motor and the cold stage.
2Ease of operation
If a motor is placed inside the dewar to actuate optical elements, then mechanical actuation is achieved, but heat interference increases and thermal mass increases
Solution Approach 1:
The translation stage serves as a thermal intermediary, extending mechanically from the warm motor through the dewar wall to the cold optical elements. This allows the motor to remain outside the dewar, actuating the optical elements without introducing its heat load into the cryogenic environment.
Solution Approach 2:
The system replaces direct mechanical coupling between motor and optical elements with a magnetic coupling mechanism. Magnets in the motor interact with magnets in the translation stage through the dewar wall, eliminating the need for physical shafts or gears that would conduct heat into the cold stage.
3Use of energy by stationary object
If the optical assembly is extended to allow motor actuation from outside the dewar, then the motor can be placed in the warm environment, but the optical path length increases
Solution Approach 1:
The translation stage is designed to be dynamically extendable and retractable along the optical axis. During operation, the stage extends only to the minimum distance required for motor actuation, allowing the optical elements to be positioned as close as possible to the detector while still enabling external motor control.
Solution Approach 2:
The motor actuation mechanism operates in a dimension perpendicular to the optical path, using magnetic fields that can penetrate the dewar wall. This allows the motor to be positioned outside the optical path while still exerting control forces on the optical elements through the translation stage.
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 enhances spectral performance by effectively cooling diffractive optical elements, reducing unwanted thermal interference, and enabling precise mechanical actuation within a compact, low-power cryogenic cooling system, thereby improving signal-to-noise ratio and maintaining image stability.
Implementation Method 1
A resilient cold shield extends from the adapter ring to a lens holder, the lens holder connected to the resilient cold shield distal from the adapter ring
Implementation Method 2
An insulating translation arm connects the motor to the optical light shield, whereby operation of the motor induces the insulating translation arm to extend or retract the optical assembly
Data Source
AI summary
A cold stage actuation system employs an optical assembly having an adapter ring mounted to a flange connected to a cold finger which extends into a Dewar housing. The flange supports a detector array. A resilient cold shield extends from the adapter ring to a lens holder, the lens holder connected to the resilient cold shield distal from the adapter ring. The lens holder supports a lenslet array. An optical light shield extends from the lens holder oppositely from the resilient cold shield to proximate a window in the Dewar housing. A motor is supported within the Dewar housing. An insulating translation arm connects the motor to the optical light shield, whereby operation of the motor induces the insulating translation arm to extend or retract the optical assembly concentric with an optical axis.