Synchrotron radiation-based quasi-elastic scattering using time-domain interferometry with mult-iline gamma rays

We developed a multi-line time-domain interferometry (TDI) system using 14.4 keV Mossbauer gamma rays with natural energy widths of 4.66 neV from Fe-57 nuclei excited using synchrotron radiation. Electron density fluctuations can be detected at unique lengths ranging from 0.1 nm to a few nm on time scales from several nanoseconds to the sub-microsecond order by quasi-elastic gammaray scattering (QGS) experiments using multi-line TDI. In this report, we generalize the established expression for a time spectrum measured using an identical single-line gamma-ray emitter pair to the case of a nonidentical pair of multi-line gamma-ray emitters by considering the finite energy width of the incident synchrotron radiation. The expression obtained illustrates the unique characteristics of multi-line TDI systems, where the finite incident energy width and use of a nonidentical emitter pair produces further information on faster sub-picosecond-scale dynamics in addition to the nanosecond dynamics; this was demonstrated experimentally. A normalized intermediate scattering function was extracted from the spectrum and its relaxation form was determined for a relaxation time of the order of 1 mu s, even for relatively large momentum transfer of similar to 31nm(-1). The multi-line TDI method produces a microscopic relaxation picture more rapidly and accurately than conventional single-line TDI.