Several physical processes can drive this removal. In many cases, the laser causes rapid thermal expansion of the substrate, creating a lifting force that overcomes the bond holding contaminant particles to the surface and effectively launches them off. For thinner layers of rust or oxide, the laser can vaporize the material outright or trigger what’s called a phase explosion, where the contaminant superheats so quickly it bursts apart. Other mechanisms include stress vibration, evaporation pressure, and plasma shockwaves at the surface. In practice, most laser cleaning involves a combination of these effects happening simultaneously.