Speaker
Description
Silicon undergoes a sub-picosecond non-thermal melting transition when excited by intense femtosecond laser pulses. This talk demonstrates how soft X-ray absorption spectroscopy (XAS), performed at the seeded FERMI free-electron laser (FEL), effectively captures this process by resolving the ultrafast electronic structure dynamics of silicon with a temporal resolution on the 10 fs timescale.
By tuning the FERMI FEL photon energy across the Si L₂,₃-edge following femtosecond UV excitation, we reveal a sub-picosecond rearrangement of the electronic structure. This excitation induces a rapid destabilization of the covalent bonds, leading to a lattice collapse before significant phonon-driven thermal effects can take place. The observed dynamics of the XAS spectrum, associated with bandgap collapse and electronic redistribution, provide direct evidence of a non-thermal melting transition.