Transient absorption of phenol derivatives dissolved in 50:50 mixture of acetonitrile (C2H3N) and water was measured. Concentration of the solution was 5 x 10-4 M while the absorbance at the pump wavelength (267nm) was 0.72 per cm.
Spectrum of the probe pulse was spread from 340nm – 575nm and probe pulse was generated in a thin (3mm) CaF2 window. Figures below show 2D diagram, wavelength cuts for 3 wavelengths and the evolution of spectra with time. Signal is entirely positive which agrees with the fact that used phenol derivatives do not fluoresce, therefore excited state absorption contributes the most.
Near time-zero, at lower wavelengths, signal of higher value is present due to artifacts of the transient absorption technique (2-photon absorption, Raman scattering, cross-phase modulation…) which lasts approximately 600fs. During the first 400fs-500fs, spectra rise to its shape which is maintained during the rest of the measurement (8ps). Measurements at longer time scales (1ns) show that the signal fades away very slowly so the time scale required for capturing the end of the signal is longer than the longest time range achievable in our experiment.