Nanosecond Transmission Studies

One weakness of postirradiation methods, i.e., analysis of the ablation properties and surface analysis, as tools for studying the ablation mechanisms of polymers is the possibility that reactions after irradiation cause the observed effect. These results are therefore only indirectly related to the abla- 

In recent studies of a photochemical model, attention was drawn to the absorption properties of the polymer during the laser pulse [132, 174]. These results were analyzed theoretically using a two-level model of chromophore absorption [175]. In this model, excited states of the chromophore are capable of photon absorption. The model is shown in Fig. 21. In Eqs. 2 and 3 the single photon absorption for ablation depth and transmission ratio is described, 

3 Th is the transmission of the laser pulse at various fluences and Tl is the transmission of the sample measured with low energy, e.g., a UV-Vis spectrometer. 

The model can be extended to two levels of excited states (Fig. 21), as described in Eq. 4 

The change in absorbance AA after irradiation was obtained from the spectra recorded by UV spectroscopy for films with a thickness of 0.21 pm. The single-shot transmission of the laser pulse (Th) was measured at various flu-ences by using an experimental setup shown in Fig. 22. The low intensity 

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All of the molecules in this study have triplet states which are easily detectable by the technique of nanosecond transmission laser flash photolysis. (11) The triplet state of acetoveratrone has a lifetime in excess of 15 ps in ethanol (Figure 2) under conditions of laser excitation the decay involves a mixture of first and second order kinetics, with the latter dominating at high laser powers. This second order decay demonstrates that the triplet state is decaying at least partly by triplet-triplet annihilation. 

One of the designed photolabile triazene polymers (Scheme 8) was selected to test whether a different behavior can be detected for these materials. In this report, decomposition dynamics of the photosensitive triazene polymer film upon intense XeF excimer laser irradiation is studied by applying the nanosecond interferometric technique with a newly improved optical setup. On the basis of the revealed morphological dynamics as well as the obtained time-resolved transmission and reflectance, the ablation mechanism and the dynamics of the triazene polymer film are discussed in detail. 

Femto- and picosecond nonlinear transmission (z scan) measurements give the intrinsic TPA coefficient (3 4.7 cm/GW, whereas nanosecond studies show that P is intensity dependent, and ranges from 4.7 at low intensity to over 170 cm/GW at high intensity. The latter is attributed to excited-state contribution, which is confirmed in picosecond dynamical pump-probe studies. " " ... 

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