Control Gold, Nickel, and Copper Emissivity
Controlling gold, nickel, and copper emissivity with mechanical solutions alone is not enough to reduce stray light from entering the detector. In addition to tight-fitting or potted wiring feedthroughs, or stepped interfaces, we also use coatings and surface processes to control the emissivity of internal system components.
Here are a few examples of the coatings and surface process options offered through IRLabs.
Coatings and Techniques to Lower Surface Emissivity
These coatings and techniques lower the surface emissivity, making it more reflective, particularly in the IR spectrum. Lowering the emissivity prevents radiative heat transfer between two surfaces of different temperatures eg between a room temperature vacuum case and a cold radiation shield.
Foil and Multi-layered Insulation
Foil and MLI applied to vacuum cases and radiation shields improve thermal performance. The adhesives used to apply these can outgas and saturate getter materials. For that reason, we usually reserve these for our 4K systems.
Surface Process: Polished Aluminum
Polishing internal surfaces of vacuum cases and radiation shields is the preferred method of reducing surface emissivity on typical cryostats. A polished aluminum surface can greatly reduce radiative heat transfer, thus improving cryogenic performance. It is an effective low-cost option when nickel, gold or other low-emissivity coatings are not required.
Low emissivity nickel can be added to internal aluminum components. Nickel plating increased the hardness of aluminum alloy but is primarily used within cryogenic systems to increase corrosion resistance. Nickel also has a relatively reflective (low emissivity) surface that can help to reduce the thermal load on a system due to radiative heat transfer.
Gold is highly reflective in the IR spectrum and is the best material to use when emissivity must be kept as low as possible. It is routinely used for space-based applications as well high-end IR mirrors. We have experience with the processes for gold coating both copper and aluminum components. It is standard practice for us to gold coat all internal copper parts.