SSCU Student Seminar
Name: Mr. Ponnamanda Karthik
Title: X-ray Free-Electron Lasers for Probing Ultrafast Structural Dynamics
Date & Time: Thursday, 08th October 2026 at 4.00 p.m.
Venue: Rajarshi Bhattacharyya Memorial Lecture Hall, Chemical Sciences Building
Abstract:
When crystals undergo a structural phase transition or chemical bond breaking, we require a probe with a temporal resolution shorter than the timescale of atomic vibrations (on the femtosecond scale) and a wavelength short enough to resolve atomic-scale structures. For decades, synchrotron storage rings have served as powerful X-ray sources for our research, in which relativistic electron bunches circulate for hours and emit radiation through bending magnets and undulators. However, synchrotron X-ray pulses are typically tens of picoseconds long, which limits their ability to resolve dynamics occurring on femtosecond timescales. X-ray free-electron lasers (XFELs) overcome this limitation by combining femtosecond pulse durations with high transverse coherence and extremely high peak brilliance. The concept of the free-electron laser originated from Madey’s theory in 1971 and was subsequently extended to the high-gain regime.
In my presentation, I will compare synchrotron radiation sources and XFELs in terms of electron-beam physics, coherence, pulse duration, peak brilliance, and repetition rate. I will then discuss how XFELs enable “diffraction before destruction” and pump–probe measurements of ultrafast structural dynamics, focusing on two case studies from the European XFEL facility. These studies demonstrate how XFELs extend X-ray science beyond the characterization of static structures. A single femtosecond pulse can capture the three-dimensional atomic structure of a crystal. The intense pulses produced by XFELs can also deposit sufficient energy to trigger chemical reactions, which can then be monitored using subsequent pulses. Finally, I will conclude my talk with some future perspectives of XFELs.
References:
B. W. J. McNeil and N. R. Thompson, “X-ray free-electron lasers,” Nature Photonics 4, 814–821 (2010).
E. Prat, “Synchrotron light sources and X-ray free-electron lasers,” arXiv:2107.09131 (2021).
G. Bortel et al., “3D atomic structure from a single X-ray free-electron laser pulse,” Nature Communications 15, 970 (2024).
H. Hwang et al., “X-ray free-electron laser-induced synthesis of ε-iron nitride at high pressures,” The Journal of Physical Chemistry Letters 12, 3246–3252 (2021).