Characterization of ultrashort white light pulses

Recently, pump-probe spectroscopy revealed of great interest to unveil the complex non-equilibrium dynamics in strongly correlated materials. In this context, we developed a method to spectrally and temporally characterize the supercontinuum pulses to be employed as broadband probes in pump-probe spectroscopic set-ups. The image shows a supercontinuum pulse spectrogram, as obtained with our technique.

The method we present consists in exploiting the optical switching behavior of a VO2 thin film, when a photoinduced phase transition is triggered by a pump pulse. In a), the time-and-frequency resolved reflectivity variation, measured on the VO2 multi-film sample, is shown. (b) Time traces at different wavelengths are reported. The solid lines are the fit to the data, as described in the text. (c) The frequency-resolved reflectivity variation at t−t′ = 0.6 ps is reported. The solid line is the reflectivity variation mimicked replacing the VO2 insulating dielectric function with the metallic one.