Extending the Reach of Extreme Ultraviolet Instruments: A New Method for Measuring the Refractive Index of Materials
Catherine Burcklen | 20-FS-026
The large discrepancies found between simulations and experimental data from extreme ultraviolet (EUV) instruments in the wavelength range 20 to 90 nanometers (nm) has been a long-standing issue in the scientific community and it has been traced to the lack of reliable refractive index values. Precise knowledge of the wavelength-dependent, complex refractive index (optical constants) of materials is required to accurately design, build and calibrate instruments in the EUV range. Until now, optical constants of materials in the wavelength range 20–90 nm have been mostly unreliable or unavailable, due to severe challenges associated with measurements in this spectral region. We proposed a new methodology that overcomes these challenges and enables accurate measurements of the refractive index in the 20–90 nm range. We validated our new method through actual measurements of the optical constants of essential materials for EUV instrumentation. This work is a breakthrough with both fundamental and practical implications: it is opening the possibility for accurate design and implementation of EUV instruments in a previously inaccessible region of the spectrum. Optical constants determined by this methodology could also be used to validate atomic physics theoretical models.
The foundational outcomes of this project benefit several Lawrence Livermore National Laboratory core competencies, including lasers and optical science and technology, by enabling access to fundamental knowledge related to optical properties of materials, interactions of EUV radiation with matter, and atomic physics. DOE mission areas that benefit from this work include plasma, solar, and planetary physics, EUV lasers, semiconductor photolithography, synchrotron and free-electron laser (FEL) science, and Electron Beam Ion Trap (EBIT) physics.