Chapter 5 - Droplet-Assisted Laser Cleaning of Contaminated Surfaces

Abstract

Surface cleaning is becoming increasingly important in modern manufacturing. Traditional cleaning processes are predominantly thermal processes and may not be applicable for the next generation of devices that include parts manufactured at the micro/nanoscale that are sensitive to heat and abrasion. This problem with such parts can be overcome by a new surface-cleaning technique called droplet-assisted laser cleaning (DALC). The DALC uses a Q-switched Nd:YAG laser to vaporize a stream of water droplets to produce a succession of impacting shock waves at the surface of the component of interest. The generated shock waves can be used for various material processing applications, including removal of contaminants. The process exploits the combined potential of laser shock cleaning (LSC) and optohydrodynamic processing through explosive vaporization of water droplets. In this chapter, we discuss traditional laser cleaning processes from direct beam/contaminant interaction to LSC. The DALC process discussed in this chapter was specifically designed to induce explosive vaporization of a 300-μm water droplet above the contaminated substrate surface. The shock pressure magnitude was analyzed using high-precision force and acceleration sensors. The effect of laser energy, number of pulses per position, gap distance and scanning speed on the cleaning performance was investigated in detail. A contaminated substrate with micropolystyrene particles was used to evaluate the performance of the DALC system, and the results, in comparison to those obtained from the traditional LSC process, show that DALC can be an excellent alternative to the existing laser-based cleaning process (ablation and shock).