Laser molecular implantation into polymer solids induced by irradiation below ablation threshold

Polymer films involving fluorescent molecules such as anthracene, diphenyl anthracene or pyrene (source films) were overlaid with neat polymer films (target films), and irradiated with nanosecond pulsed laser from the rear of the target films. Fluorescent patterns of these molecules 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 the reduction of fluorescence intensity. It was found that the lower the glass transition temperature of the source film, the higher the amount of ejected molecules. The thickness of the implanted layer at the surface of the target film was obtained by means of total internal reflection fluorescence spectroscopy. The amount of molecular aggregates was found to increase with increasing the number of laser shots. The mechanism of the penetration and aggregation of the fluorescent molecules by repetitive irradiation was discussed in connection with photothermal temperature jump and thermally activated diffusion in polymer solids.