FEL-induced ultrafast IR reflectivity change
A FEL pulse impinging on a target interacts with its electrons, promoting in a few femtoseconds a large amount of them from their equilibrium states to higher energy bands, before thermalization and recombination bring the system back to equilibrium in a nanosecond time scale.
Casolari et al., Applied Physics Letters 104, 191104 (2014).
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Impinging with an infrared pulse with controlled delay after a FEL pump pulse allows to investigate the electron dynamics through the measurement of variations in IR reflectivity. The different behavior of several kinds of solid samples have been tested, using a 100 fs FEL pulse as a pump, followed by a 150 fs IR probe, obtained splitting the same laser pulse used to seed the FEL process. The very various response of Si3N4 samples with different thicknesses and substrates is showed to be consistent with an interferometric model assuming identical excitation for the same surface layer of each sample. |
FEL pump and IR probe are naturally synchronized, coming from the same seed pulse: the only gitter between the two sources, due only to mechanical instability in the beam propagation setups, is estimated around 15 fs. Retrieve articleRole of multilayer-like interference effects on the transient optical response of Si3N4 films pumped with free-electron laser pulses. F. Casolari, F. Bencivenga, F. Capotondi, E. Giangrisostomi, M. Manfredda, R. Mincigrucci, E. Pedersoli, E. Principi, C. Masciovecchio, M. Kiskinova. Applied Physics Letters 104, 191104 (2014). DOI: 10.1063/1.4875906 |
