Wet/steam laser cleaning (WLC) uses a liquid layer that strongly absorbs the laser wavelength being use. As shown in Fig. 7.3a, laser irradiation can rapidly heat and evaporate the liquid, and this can force the particles from the surface [3]. Alternatively, the workpiece may be keep in an atmosphere of enhance humidity, which results in capillary- condense water [4]. Steam laser cleaning uses a very thin liquid layer, which is condense onto the substrate surface. The liquid layer is superheat (and evaporat), and causes the nucleation and growth of bubbles at the liquid–solid interface. This results in high pressure below the contaminant (Fig. 7.3b) that can be strong enough to remove the particle from the surface. In general, steam and wet laser cleaning require lower laser fluences for particle removal than dry laser cleaning. Although application of liquids to the substrate may not always be practical.

Many researchers have shown that

the rapid vaporization of a transparent water film in contact with an opaque surface produces a shock pressure pulse at the liquid–solid interface.

The wet laser cleaning process uses shock pressure to remove the contaminants. Which in some cases can be higher than the thermodynamic critical pressure. The efficacy of WLC has been demonstrated for various applications, including removal of microparticles from a bulk surface [6]. In a typical WLC process, the saturat vapor is apply over the sample prior to the laser irradiation and a thin liquid–water film is produce by condensation of the liquid vapor.

Experimental results have shown that both IR (infrared) and UV (ultraviolet) laser pulses can be used to remove 0.3 μm particles from nickel alloy substrates at relatively low fluence, without inducing any substrate damage [7]. Experimental results with different contaminant/substrate sample systems, including epoxy film on metal surfaces and alumina particles. Show that the WLC with appropriate laser parameters can be very efficient in removing a range of contaminants from solid surfaces, especially in removing microparticles.