Ultrafast Hyperspectral Transient Absorption Spectroscopy: Application to Single Layer Graphene

We describe the basic principles and the experimental implementation of the hyperspectral transient absorption technique, based on femtosecond laser sources. In this technique the samples were optically “pumped” using the femtosecond tunable pulse delivered by an Optical Parametric Amplifier, and “probed” for changes in transmission in a broad spectral range with a “white light” laser-generated supercontinuum. The spectra were collected by a pair of multichannel detectors which allowed retrieval of the absorbance change in a wide spectral range in one time. The use of the supercontinuum probe introduced artifacts in the measured 2D data set which could be corrected with a proper calibration of the chirp. The configuration with crossed polarization for pump and probe pulse extended the spectral measured range above and below the pump energy within the same experiment. We showed the versatility of the technique by applying it to the investigation of the charge carrier dynamics in two-dimensional single layer graphene.