Speaker
Description
This talk will focus on coherence properties of femtosecond fluorescence produced by pumping the transition metal elements with X-ray free-electron laser (XFEL) pulses.
When the intensity of the incident beam is sufficiently low, the fluorescence will be incoherent light. The higher-order coherence of such incoherent light, especially intensity correlation between separated positions, provides rich information about the incident pulses, such as pulse duration and shape [1,2], as well as beam size on the target [3]. In the first half of my talk, I will discuss spatiotemporal diagnostics of XFEL pulses using fluorescence and their advantages over existing techniques while presenting the results obtained at SPring-8 Angstrom Compact free-electron LAser (SACLA) [4-6].
When the pump intensity is sufficiently strong to induce population inversion between inner-shell states (e.g., 1s and 2p states), the fluorescence photons become collective and exhibit directionality [7]. This coherent radiation, known as amplified spontaneous emission, can serve as the basis for an X-ray laser oscillator that generates fully coherent pulses by combining with cavity optics [8]. In the second half of my talk, I will talk about the coherence properties of amplified spontaneous emission. Based on the experimental results at SACLA and theoretical simulation, I will discuss the feasibility of an X-ray laser oscillator and requirement for X-ray optics.
[1] M. Yabashi, K. Tamasaku, T. Ishikawa, PRL 87, 140801(2001).
[2] I. Inoue et al., Phys. Rev. Acc. Beams 21, 080704 (2018).
[3] M. Yabashi, K. Tamasaku, T. Ishikawa, PRL 88, 244801 (2002).
[4] I. Inoue et al., J. Synchrotron Rad. 26, 2050 (2019).
[5] N. Nakamura et al., J. Synchrotron Rad. 27, 1366 (2020).
[6] I. Inoue et al., PRL 127, 163903 (2021).
[7] H. Yoneda et al., Nature 524, 446 (2015).
[8] A. Halavanau et al., PNAS 117, 15511 (2020).
