Structure induced by irradiation of femtosecond laser pulse in dyed polymeric materials

We investigated the structures induced by an irradiation of a near-infrared (NIR) femtosecond laser pulse in dye-doped polymeric materials {poly(methyl methaerylate) (PMMA), thermoplastic epoxy resin (Epoxy), and a block copolymer of methyl methacrylate and ethyl acrylate-butyl acrylate [p(MMA/EA-BA) block copolyiner]}. Dyes used were classified into two types-type 1 with absorption at 400 nm and type 2 with no absorption at 400 nm. The 400-nm wavelength corresponds to the two-photon absorption region by the irradiated NIR laser pulse at 800 nm. Type I dye-doped PMMA and p(MMA/EA-BA) block copolymer showed a peculiar dye additive effect for the structures induced by the line irradiation of a NIR femtosecond laser pulse. On the contrary, dye-doped Epoxy did not exhibit a dye additive effect. The different results among PMMA, p(MMA/EA-BA) block copolymer, and Epoxy matrix polymers are supposed to be related to the difference of electron-acceptor properties. The mechanism of this type 1 dye-additive-effect phenomenon for PMMA and p(MMA/EA-BA) block copolymer is discussed on the basis of two-photon absorption of type 1 dye at 400 nm by the irradiation of a femtosecond laser pulse with 800 nm wavelength and the dissipation of the absorbed energy to the polymer matrix among various transition processes. Dyes with a low-fluorescence quantum yield favored the formation of thicker grating structures. (C) 2002 Wiley Periodicals, Inc.