Figure 1: Pump-probe set-up.
From: Ultrafast collinear scattering and carrier multiplication in graphene
(a) A pump and a probe pulse, with different colours, impinge on a sample with a variable delay. The spectrum of the probe pulse through the sample is measured by a spectrometer. (b) MDF bands in graphene, εk,s=sv|k| with s=±1 and 
m s−1. Pump (blue arrow) and probe pulses (red arrow) are applied at different photon energies in a hole-doped sample. The electron distribution relaxes towards the Dirac point by losing energy. Electrons (grey circles) transfer energy to other degrees-of-freedom (dashed arrows), such as phonons and other electrons in the Fermi sea. When half of the probe-pulse energy matches the maximum of the electron distribution, absorption is strongly suppressed by Pauli blocking (red cross) and the transition is ‘bleached’.
