1.3 Angular Laser Cleaning

In contrast to typical laser cleaning, the angular laser cleaning technique irradiates the contaminant surface at a glancing angle. This is claimed to drastically improve the cleaning efficiency by 10 times compared to typical laser cleaning that uses perpendicular irradiation [8,9]. However, its effectiveness is dependent on the surface characteristics and the size of the contaminants.

1.4 Laser Shock Cleaning

In laser shock cleaning (LSC), a high-intensity laser is focus onto a tight spot, slightly above the sample to be clean. But the laser-induced breakdown (LIB) of the gas produces a strong shock pressure wave. Which impinges onto the surface to be clean. It has been shown that laser shock cleaning is effective for removal of nanoparticles.

Lim and Kim have shown that the LSC technique can be combine with liquid-phase chemical cleaning for removal of oxide layers. In the modified process, LIB occurs within a liquid solution and the shock pressure generated in the liquid significantly accelerates the cleaning process. In another work by Lim and Kim, the influence of the laser-induce shock waves under various gases was characteriz using the laser flash photography and the optical beam deflection process. Experimental results of the shock wave propagation show. That the optical breakdown of gases (air, He, N₂, Ar) by a nanosecond-pulsed Nd:YAG laser could produce shock waves with a speed in the order of 1000 m/s and pressure intensity around 1 MPa.

1.5 Laser-Assisted Optohydrodynamic Cleaning

In short, cleaning of submicron particles is always a challenging task. Ahn developed a laser-based spray material processing technique for cleaning of submicrometer particles. In this process, a high-speed (~ 1600 m/s) submicrometer liquid jet produced with the aid of laser-induced plasma is used for material processing applications, including laser cleaning. shows the mechanism of a typical optohydrodynamic cleaning process. In this process, laser-induced breakdown of a micrometer-sized water droplet produces a high-speed jet (with speeds up to 1600 m/s). Which removes particle contaminants from the substrate. The performance of the optohydrodynamic cleaning process depends on various factors. Including laser energy, the relative position of the droplet, the gap distance between the droplet and the surface. And number of pulses per position (NOP).

However in 2016, López et al. proposed droplet-assisted laser cleaning (DALC) as a new manufacturing technique. That exploits the combined potential of laser shock processing and optohydrodynamic processing through explosive vaporization of liquid droplets. The DALC uses a 355 nm 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. Therefore, we can use the generated shock waves for various material processing applications, including cleaning of contaminants.