EXAFS for probing thermal states of compressed materials at NIF

EXAFS (Extended X-ray Absorption Fine Structure) refers to the oscillatory modulations in x-ray absorption spectra above an absorption edge, generated by interference between photoelectron waves and scattering by neighbor atoms. EXAFS is sensitive to temperature of materials in the range of 100-10000K because ionic thermal motion reduces the coherence of the interference, leading to decay of the modulations. This talk will give a brief overview of the EXAFS platform at NIF, including development of a bright continuum backlighter [1], a high-resolution spectrometer [2], and a novel shape of crystal to achieve both high throughput and high resolution [3]. Excellent EXAFS data at K-edge have been obtained for Fe compressed up to 8 Mbar and Cu up to 10 Mbar. The EXAFS measurements at L-edge are more challenging due to smaller EXAFS amplitude. The high x-ray flux at NIF has enabled L-edge measurements for higher-Z materials such as Ta and Pb. The prospect of such a new capability at NIF for probing thermal states of compressed materials will be discussed.