KrF laser ablation of polyurethane

Abstract

248 nm excimer laser ablation of a polyurethane polymer is shown to proceed efficiently and with a surprising lack of post-ablation surface debris. The absorption spectrum of this material displays a strong increase in absorbance beginning at 260 nm and extending to shorter wavelengths, whereas a relatively weak absorption for longer wavelengths accounts for the inability of 308 nm excimer radiation to cause efficient ablation. Ablation rate versus incident fluence data were obtained by both conventional stylus profilometry and the higher precision quartz-crystal microbalance (QCM) method. The data from both methods were in agreement, although the QCM technique provided far more detail of the threshold region. Interestingly, near 35 mJ/cm2 incident fluence, a pronounced increase in the slope of the rate versus fluence curve appears. This is suggestive of a mechanistic change from a lower to higher efficiency ablation regime. Applying a conventional Beer's Law analysis of rate versus In(fluence) yields a straight line that agrees well with the data up to 300 mJ/cm2. In face, the absorption coefficient derived from the slope of this curve is within 4% of the experimentally determined low-level value.