The next generation of detectors for high energy observatories needs a significant improvement in filter technology, as identified in the SBIR solicitation and as a PCOS technology gap. We propose a two-fold change in the state of the art of thin film EUV and x-ray filters, using Al-Sc alloy in place of Al and adding Au nanoparticles to polyimide. Al-Sc alloys show smaller grain sizes that should translate to increased strength and decreased optical/IR transmission, even for alloying fractions <1% that would not noticeably impact the x-ray spectrum. Surface plasmon resonances (SPR) in Au nanoparticles allow tunable absorption peaks for optical thermal control and baking. Since SPRs effectively enlarge the absorption cross section of nanoparticles, we expect to achieve a narrowband visible optical depth of ~0.2 with an x-ray transmittance of >95% (nanoparticles only). We lay out a fabrication and testing plan to push these technologies from TRL2 to TRL4 by the end of Phase I by demonstrating heating of doped films, optical and infrared density of alloyed films, and beamline measurements of x-ray transmittance and density of constituent species in integrated Al-Sc/doped polyimide filters.
This work targets the requirements of large-format thin film filters for high-energy observatories. Increased strength and optical density for metal layers and non-contact thermal control will improve the state of the art of optical and infrared blocking filters and contamination blocking filters. Increased strength of Al via alloying also improves its usefulness as a window in low-pressure differential laboratory gas cell experiments to characterize aerosols and model planetary atmospheres.
Increased optical/IR density and thermal stability afforded by alloying Al is directly applicable to IR-pumped high harmonic generation laser experiments, free electron lasers, synchrotrons, and x-ray instrumentation and metrology tools where pure Al is the current standard. Inertial confinement fusion experiments have a need for resonant absorption of doped polyimide, where pre-heating lasers can remove polyimide layers in the microseconds prior to a shot.