The induced anisotropy results in a change of the probe beam polarisation after interaction within the sample. This change is recorded for each wavelength of the continuum. Intensity measurements are averaged over 120 shots for each angle of the analyser. The spectral dependence of df is directly related to that of the absorbance, while its time dependence provides information both on the excited state relaxation dynamics and on the molecular orientational diffusion inside the solvent. Practically, it is dominated by bleaching of the main absorption band, corresponding to the linear absorption of the normal form at 490nm.
Base line is shifted upward for clarity.
The sharp peak at 532nm is due to pump scattering. This confirms that with this solvent, the B isomer is not formed upon optical excitation. The signal is observed to decrease rapidly, with a monoexponential decay time t . This shows that signal decay is dominated by the excited state lifetime of the molecule. The Kerr signal is dominated by bleaching of the band corresponding to the linear absorption of the normal form at 490nm.