Researchers at Lawrence Livermore develop and deploy coating technologies to enable novel observations in the x-ray and extreme ultraviolet wavebands.
Developing multilayer coating technologies
Multilayer interference coatings are an enabling element of optical components for extreme ultraviolet (EUV) and x-ray observatories, providing capabilities for solar physics, planetary physics, and astrophysics. Multilayers consist of stacks of alternating thin film layers of two or more materials deposited on an optical substrate. The constructive interference between the layers results in high reflectance.
In the EUV and soft x-ray region (1–100 nanometers [nm]), multilayers can provide high reflectance at near-normal incidence, a regime where a single layer of any material would have zero reflectance. In the hard x-ray, multilayers are used to create high efficiency optics that operate at extremely shallow grazing incidence angles (hundredths of a degree) and require coating layers with sub-nanometer thicknesses, corresponding to just a few atoms of material.
Researchers at LLNL develop state-of-the-art multilayer coatings and implement them for space missions. Using capabilities including advanced metrology and in-band characterization techniques, materials science and modeling, and optical design, we can identify and study limitations of multilayer technologies and provide robust solutions for improving optics from the EUV to gamma-ray wavebands.
From left: Jennifer Alameda, Regina Soufli, Jeff Robinson, Marie-Anne Descalle, and Catherine Burcklen in front of the Mag-1 deposition system with its lid open. Four sputtering sources (materials) used in thin film depositions are inside the Mag-1. Two sources are 100 mm in diameter and the other two are rectangular, 127x250 mm2 in size.
Leveraging state-of-the-art modeling capabilities, deposition facilities, and measurement facilities
Designing and fabricating multilayer coatings involve many challenges:
- Determining multilayer systems with high reflectance, appropriate spectral selectivity, and stable performance over time, for the specific wavelength region of operation.
- Addressing the sensitivity of materials to degradation mechanisms such as contamination, oxidation, and corrosion.
- Determining accurate refractive index values, including near absorption edges, which are essential for the reliable design of multilayer coating systems.
- Meeting stringent requirements for surface figure and surface roughness on optical substrates with various shapes and geometries (planar, curved, nested).
We address these challenges by studying the physics of periodic (narrowband) and aperiodic (broadband) multilayer coatings with nanoscale layers, including the crucial interfaces between layers, and by developing new multilayer material systems with improved properties. For hard x-ray applications, we improve performance by developing multilayer coatings with the thinnest achievable layers. We advance multilayer design algorithms, deposition methodologies, characterization methodologies, and corrosion barriers for extended lifetime stability.
Accurate substrate specification and metrology are an integral part of the development of these optical systems and represent one of the key competencies at LLNL. We implement state-of-the-art metrologies for measurements of surface figure and roughness of optical substrates for space applications.
