Time-Resolved Microscopy Analysis of Laser Photothermal Imaging Media

Methods for understanding the fundamental mechanisms of laser photothermal imaging are described and applied to model imaging media. The light response is characterized with a series of Gaussian laser pulses of varying intensities and durations. The results are compared to a reference model, the "local fluence" model, that assumes the likelihood of exposure at a given pulse duration depends solely on the laser fluence received at that location. The mechanisms underlying the material behavior are studied with time-resolved microscopy using a variety of exposure and viewing conditions. The imaging media have in common a silicone rubber (polydimethylsiloxane) coating that can be removed by a single laser pulse to form an imaged spot that attracts ink. They differ in having a thin-film absorber layer, a volume absorber layer, or a combination of volume absorber and energetic underlayer. The thin-film media are the least sensitive with longer duration microsecond pulses but the most sensitive with nanosecond pulses, which is explained using a thermal conduction model. The volume absorbing media show deviations from the local fluence model that indicate the existence of useful dot gain properties which improve sensitivity. Time-resolved microscopy shows that this dot gain results from high-speed mechanical effects caused by hot gas trapped under a silicone rubber balloon.