Optical seminar. Mogunov

Iaroslav Mogunov (Ioffe Institute)
‘Picosecond acoustics and ultrafast phase transition in VO2’

Abstract: The talk is devoted to my PhD research conducted in Ioffe Institute with ultrafast photonics and phononics. There, we studied VO2 – a material with a photo-induced phase transition (PIPT), which transforms from semiconductor to metal within tens of femtoseconds and changes its lattice within a few picoseconds after illumination by femtosecond laser pulses. First, we used a pump-probe technique to analyze picosecond strain pulses launched into substrate due to the PIPT in VO2. We found a significant ~0.5% dynamical strain generated due to ultrafast lattice transformation – a mechanism which consumes heat rather than dissipating it. Secondly, we investigated the reversed idea – how picosecond strain pulse would affect the ultrafast PIPT in VO2? With the help of two-pump-one-probe setup we found a ~1% change of PIPT efficiency caused by the presence of dynamical strain, with full control over the sign and amplitude of this effect. Overall, our findings show that ultrafast phase transitions are cool for inherently non-thermal picosecond acoustics.