A high-sensitivity in situ optical diagnostic technique for laser cleaning of transparent substrates

Abstract

A differential optical transmission technique has been used to monitor in situ the efficiency of laser cleaning for the removal of sub-micrometer-sized particles on substrates transparent at the monitoring wavelength. This technique has been applied to the removal of sub-micrometer polystyrene particles on polyimide substrates using laser pulses of 30 ps duration at 292 nm while probing the material transmission at 633 nm. The sensitivity achieved -1/104 for the transmission changes induced upon single-pulse laser exposure - allows us to monitor the removal of just a few sub-micron-sized particles from the probed region inside the irradiated area.