3.1 Dry Laser Cleaning Method

The DLC approach was the first method employ to remove particles from substrates using lasers. Various academic and industrial research groups have reported the experimental, characterization and computational results of this cleaning method in the past [33–46]. In the dry laser method of cleaning, a short-pulse laser beam is direct on the substrate that has to clean. This laser pulse excitation on the substrate results in rapid thermal expansion and thermomechanical wave propagation and out-of-plane acceleration. Thereby exciting the substrate and/or the particles that have to remove. This high-frequency (nanosecond) acceleration and wave propagation phenomenon generates an inertial force. That can shake off the particle adhered to the substrate, provided the generated inertial force exceeds the total adhesion force consisting of several individual forces. Such as van der Waals, electrostatic, and capillary forces.

The main principle of this mode of sub-micrometer particle removal is the substrate acceleration induced by the thermoelastic field generated by the irradiation of the short-pulsed laser.

The substrate attains its maximum acceleration value. Due to the substrate thermal expansion during the irradiation of the short-pulsed laser in the out-of-plane direction. Until the peak fluence of the beam is reach. The resulting positive acceleration presses the particle down and increases the contact diameter and the strain energy stored in the deformed particle. Removal can occur only after the surface begins to decelerate. The magnitude of surface acceleration is proportional to the level of fluence. Due to linearity assumption of thermoelastic effects and is inversely proportional to the duration of the laser pulse squared. However, above a certain level of laser fluence, thermal and/or mechanical damage on the surface could occur [46]. It is also noteworthy that during this process the surface is subject to high levels of electromagnetic radiation as well.