MODEL FOR BURNING KINETICS AND SHAPE OF FLUENCE-SATURATED SPECTRAL HOLES

We propose a simple model for the study of fluence-broadened holes. The model is based on a strong dispersion of the burning rates and the burning process takes place over several decades of fluence. In this so-called semi-saturated regime, the hole depth varies almost linearly with the logarithm of the fluence and the hole width increases as the power 0.25 of the fluence, i.e. exponentially with the hole depth. A careful study of semi-saturated holes could allow us in principle to determine the homogeneous width free from the contribution of spectral diffusion. The hole shape is also discussed and can often be fitted either by Lorentzian or by logarithm of Lorentzian profiles. Several examples of semi-saturated holes can be found in previous works in the literature. As a further instance, we present our results on free-base tetraazaporphin in a Langmuir-Blodgett film. The reasonable agreement with the model allows us to evaluate the rate dispersion in this system and to ascribe it to barrier height fluctuation induced by the disordered molecular surrounding. © 1990.