Development of ultrashort intense broadband laser-plasma x-ray source for ultrafast Laue x-ray diffraction.

Laue x-ray diffraction (LXRD) is a commonly used experimental technique to investigate the crystal structure of single-crystalline solids using a polychromatic x-ray source, enabling simultaneous measurement of multiple Bragg peaks; however, it lacks time information. Using an ultrashort pulse duration polychromatic x-ray source can demonstrate ultrafast Laue x-ray diffraction (ULXRD) pump-probe studies, providing comprehensive insights into ultrafast structural evolution by concomitantly measuring the evolution of various reciprocal lattice planes. Here, we present the development of an ultrashort (∼300 fs) intense broadband (up to 100 keV) laser-plasma x-ray source by optimizing the laser parameters and demonstrate a ULXRD study in EuTe4 sample, a charge-density-wave (CDW) compound. We find that for laser-plasma sources driven by mJ, fs laser systems, the high laser pre-pulse contrast can significantly enhance the Cu Kα x-ray flux [∼3 × 1010 photons/(sr s)] and extend the Bremsstrahlung background (up to 100 keV). Further, the Cu Kα flux increases sub-linearly with laser pulse energy, which paves the way to generate an even stronger x-ray source using multi-kHz high average power fs lasers having relatively smaller pulse energy. With the broadband source, we measured 11 diffraction peaks simultaneously in a single sample orientation in the LXRD pattern. Careful control of experimental parameters enabled us to record the dynamics of the weak-intensity CDW peak in the ULXRD study. Currently, the source has ∼±10% shot-to-shot fluctuation. Efforts are underway to reduce it to <1%, enabling us to investigate relatively low-intensity modulation of Bragg peaks after photoexcitation.