2023-11-27 12:45:06
The Habitable Worlds Observatory (HWO) is a future NASA mission that, as its name suggests, will focus on the study of potentially habitable planets.
The Habitable Worlds Observatory will be sensitive not only to light with wavelengths visible to humans, but also to infrared and ultraviolet.
One of the instruments proposed for missions of this type is the LUMOS spectrograph, designed to revolutionize high-resolution spectroscopy and whose imaging channel would greatly benefit from better far-ultraviolet filters.
LUMOS (LUVOIR Ultraviolet Multi Object Spectrograph) is a multi-object spectrograph that spans from 100 nanometers to 1000. That covers a good part of the far ultraviolet, visible light and even a little of the near infrared band. LUVOIR (Large UV/Optical/IR Surveyor) is, like the Habitable Worlds Observatory, an ambitious space observatory proposed for the future.
Researchers from the Materials Microanalysis Center of the Autonomous University of Madrid (UAM) in Spain, the Optics Institute of the Higher Scientific Research Council (CSIC) in Spain and the NASA Goddard Space Flight Center in the United States completed recently a work aimed at optimizing for the first time a new reflective optical coating that can be used in optical devices operating in the far ultraviolet.
The new optical coating seeks to meet the necessary improvements in far-ultraviolet light detection needed by the Habitable Worlds Observatory mission and other future observatories.
A step in the deployment plan of the LUVOIR observatory. (Image: NASA)
To achieve better filters in the far ultraviolet, it is essential to provide them with a very high reflectance and make them very sensitive to changes in wavelength. Multilayer fluoride coatings are currently the best option, but need to be improved for the next generation of space missions.
The design of mirrors and optical filters capable of efficiently reflecting far ultraviolet light today poses a great technological challenge. In this part of the electromagnetic spectrum, below 200 nanometers in wavelength, most materials strongly absorb radiation due to the high energies involved. This greatly reduces the availability of substances with low absorption that can be used in UV mirrors. At these wavelengths, quantum effects are relevant in the light-matter interaction, making it very difficult to accurately predict and control the refractive indices and other characteristics of each new material. This complicates the design of new multilayer coatings, where nanometric control of layer thicknesses is required.
In the new study, Paloma López Reyes’ team, from the CSIC Institute of Optics, has characterized the layer roughness, grain size and mixing problems between layers of the coatings using atomic force microscopy and ion spectrometry. formed by alternating layers of aluminum fluoride and lanthanum fluoride. The authors of the study have compared it with traditional magnesium and lanthanum fluoride systems. The results show that aluminum and lanthanum coatings have fewer structural defects.
In theory, the more bilayers used, the more the reflectance increases, but surface roughness and other defects also increase. In the study, it was found that the optimal number was 15 bilayers that with the AlF3/LaF3 multilayer coatings managed to reflect 87% of the ultraviolet light with a wavelength of 121.6 nanometers compared to 75% with the multilayer coatings of MgF2/LaF3.
This work lays the foundation for optimizing the design of ultraviolet optical mirrors and filters that will be essential for NASA’s next generation of large space telescopes, accelerating scientific progress in this crucial but still underexplored part of the electromagnetic spectrum.
In addition to the new generation of space telescopes, other technological fields can benefit from advances in far-ultraviolet reflective coatings. These include excimer laser optics, which is a type of ultraviolet laser. Far-UV coatings may also be useful in fields such as thermonuclear fusion reactors for hydrogen characterization and also in the microchip manufacturing industry using lithography.
The study carried out by Paloma López Reyes’ team is titled “Unveiling the effects of the surface and in-depth nanostructure on the far-UV optical reflectance of thin fluoride multilayer coatings”. And it has been published in the academic journal Applied Surface Science. (Source: Institute of Optics / CSIC)
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