Here we have some of the latest results of our experiments using ultrafast spectroscopy.

Our main tool is an OPG system capable of generating 800 nm amplified Ti:Sapphire pulses  with several uJ in energy.

The pulse width is 120 fs, as measured using 2nd harmonic generation in a BBO crystal

This pulses allows to observe ultrafast processes. For instance, here is the normalized metal-semiconductor phase transition of VO2 (thin film and nanoparticles). The pump beam induces the transition which is probed by a delayed low intensity beam. As can be seen, the transition is a true step (at least at this time resolution) and we can set 120 fs as its superior limit.  At this speed, it is clear that the atomic rearrengement is happening in a single period of atomic vibration.

This source can be used to feed an OPA system to tune the laser wavelight in a wide range of frequecies, from the visible to the near IR. Using this configuration at 560 nm, We have measured the time relaxation of surface plasmons in gold nanoparticles

Furthermore, the high fluence of the 800 nm pulses can used to generate a super continum white light. This while light can be used a probe to investigate the spectral respnse of an ultrafast phenomena.

Here, we show the white light probing of the VO2 phase transition. Both phases of the VO2 present similar optical properties in the visible, but the metallic state happens to have less optical transmittance in the IR. Therefore, as show in the figure, the IR wavelengths show a step down, while the visible remains  unaffected.