LASER MOLECULAR IMPLANTATION INTO POLYMER SOLIDS INDUCED BY IRRADIATION BELOW ABLATION THRESHOLD

Polymer firms involving fluorescent molecules such as anthracene, diph enyl anthracene or pyrene (source films) were overlaid with neat polym er films (target firms), and irradiated with nanosecond pursed laser f rom the rear of the target films. Fluorescent patterns of these molecu les were found at the surface of the target films even when the laser fluence was less than the ablation threshold of the source films. The amount of ejected molecules from the source film was estimated from th e reduction of fluorescence intensity. It was found that the lower the glass transition temperature of the source film, the higher the amoun t of ejected molecules. The thickness of the implanted layer at the su rface of the target film was obtained by means of total internal refle ction fluorescence spectroscopy. The amount of molecular aggregates wa s found to increase with increasing the number of laser shots. The mec hanism of the penetration and aggregation of the fluorescent molecules by repetitive irradiation was discussed in connection with phototherm al temperature jump and thermally activated diffusion in polymer solid s. (C) 1997 Elsevier Science S.A.