Atomic Layer Deposition-Enhanced Far-to-Mid Infrared Camera Coating
Materials and Coatings
Atomic Layer Deposition-Enhanced Far-to-Mid Infrared Camera Coating (GSC-TOPS-377)
Durable and Thin Low-Reflective Absorptive Control Coating for Far-to-Mid Infrared Cameras
Overview
Infrared (IR) cameras for space missions require robust coatings that are cryogenically cooled to reduce thermal noise and are low-reflectance absorptive to mitigate image artifacts such as glinting, ghosting, and internal reflections. Thermal noise reduction improves as temperatures decrease (e.g., below 30 K). However, capturing the far-to-mid IR spectrum typically requires thick layers of common 'super black' coatings, which often use free-standing nanotubes or foam-like structures that become fragile below 120-150 K.
In response, engineers at Goddard Space Flight Center developed an Atomic Layer Deposition (ALD)-Enhanced Far-to-Mid IR Camera Coating that can be cooled to and operate at less than 30 K while maintaining low-reflection absorption. The coating results in enhanced optical performance, increased strength, reduced total mass, and suitable ionizing radiation control.
The Technology
The ALD-Enhanced Far-to-Mid IR Camera Coating is fabricated by first applying a conductively loaded epoxy binder ~500 microns thick onto a conductive metal substrate (e.g., Cu, Al). This serves to provide high absorptance and low reflectance at the longest wavelength of interest, as well as to provide a mechanical buffer layer to reduce coating stress. Borosilicate glass microspheres are coated with a thin film metal via ALD, essentially turning the microspheres into resonators. That film is optically thin in the far infrared and approximates a resistive (~200 ohms per square) coating. Light trapped in the borosilicate glass microspheres is reflected back and forth within the glass–at each contact point, the light is attenuated by 50%. A monolayer of thin metal film-coated borosilicate glass microspheres is applied to the epoxy binder and cured, forming a robust mechanical structure that can be grounded to prevent deep dielectric charging by ionizing radiation in space. Once cured, the far-to-mid IR absorber structure can be coated with a traditional ~20-to-50 microns “black” absorptive paint to enhance the absorption band at short wavelengths, or a “white” diffusive paint to reject optical radiation. At this thickness and broad tolerance, the longwave response of the coating is preserved. Tailoring the electromagnetic properties of the coating layers and geometry enables realization of a broad band absorption response where the mass required per unit area has been minimized.
While NASA originally developed the ALD-Enhanced Far-to-Mid IR Camera Coating for the Stratospheric Observatory for Infrared Astronomy mission, its robustness, absorptive qualities, and optical performance make it a significant addition to IR and terahertz imaging systems. The IR camera coating is at Technology Readiness Level (TRL) 3 (experimental proof-of-concept) and is available for patent licensing.


Benefits
- Cryogenic Strength: Superior low temperature production and operational durability allows for operation in austere environments.
- Enhanced Absorption: Detects and resolve a wider spectrum of thermal radiation, providing enhanced ability to capture faint or distant thermal signatures.
- Lightweight: Less mass per unit area results in increased efficiency payload capacity.
- Ionizing Radiation Control for IR: Dissipative and grounded components control deep dielectric charging.
- Customizable: Tunable design can absorb or reject optical radiation for passive cooling applications.
Applications
- Astronomy: Lightweight coating is ideal for size- and weight-conscious space observation instruments.
- Aerospace and Defense: Enhances infrared detection systems in aircraft and UAVs for improved surveillance, navigation, and threat detection in low-light or night operations.
- Monitoring of Space Debris: Durable, effective, and thinner coatings may benefit monitoring technologies using IR and terahertz imaging systems.
- Environmental Monitoring: Supports high-resolution infrared sensors for monitoring environmental conditions such as wildfire detection, pollution tracking, and climate change studies in particularly austere environments.
- First Responders: night vision and enhanced imaging capability in fog, rain, and smoke for search and rescue, firefighting, threat detection, and surveillance.
Technology Details
Materials and Coatings
GSC-TOPS-377
GSC-18705-1
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