The DIVE principle – the mechanism behind PIRL
Desorption by impulsive vibrational excitation (DIVE) represents a novel mechanism for laser ablation  that is suitable for all different kinds of water-containing samples. During a typical laser ablation procedure, material is removed from a surface by focusing a pulsed laser beam on a target area, the result being evaporation or plasma formation and ejection. While the DIVE principle keeps important benefits from this technique, i.e. high precision and contactless operation, it adds significant new ones by creating a special ablation regime. The PIRL laser system’s pulses feature a wavelength of 3 µm and pulse durations on the order of 100 ps, designed to be resonantly absorbed by water molecules. The laser radiation directly excites vibrational modes – specifically, the asymmetric O-H stretch – of the H2O molecule. The vibrational absorption leads to very effective energy transfer directly to translational motion of neighboring water molecules. This energy exchange is limited in two ways: The strong coupling of water molecules to each other leads to a dominant transfer to other water molecules and the effectiveness of this transfer leads to a very much localized heating process. The 100-picosecond timescale of the pulses, together with the whole heating and ablation process, means that the surrounding non-water tissue is not significantly heated before the heated material is already ejected.
- Franjic, K., et al., Laser selective cutting of biological tissues by impulsive heat deposition through ultrafast vibrational excitations. Optics express, 2009. 17(25). PubMed