Transient absorbance of two doped polymers, poly(methyl methacrylate) with pyrene or biphenyl, at the excitation wavelength was measured under laser ablation conditions. The fluence dependence of the etch depth was explained in terms of absorbance changes due to transient species and scattering by ablated fragments. The total energy absorbed at the threshold was confirmed to be almost identical, independent of the dopant. The number of photons absorbed per dopant was about 12 at the threshold, which will be discussed on the proposed model.
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