Relaxation of the singlet exciton

In P-TS6 energy relaxation times could be resolved at wavelengths below 700 mn. As the relaxation times are of the same order of magnitude as the laser pulse width (1 ps), a model function has to be fitted to the measured curve to obtain the relaxation (Fig. 9.49). 

The DFWM signal decays with half the time constant of the exciton density. For measurements of the relaxation time, the pump-probe experiments described below are to be preferred, because the intensity-dependent transmission directly follows the exciton lifetime [120], 

In the off-resonant regime at 760 nm, the Ufetime is about 0.5 ps, rising to more than 2 ps at 680 nm (Fig. 9.50). As with DFWM measurements, the lifetime can not be seen as an exponential signal decay, but as a broadening of the laser pulse autocorrelation signal. The lifetime 

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