No abstract

A method using shock tubes for amplifying the dynamic pressure of Laser Induced Plasma (LIP) shockwaves for removing sub-100-nm nanoparticles is introduced and demonstrated. The higher the amplitude of the pressure generated, the smaller the particles that can be removed and, thus the more useful for a variety of applications. Constraining the expansion of the LIP core with a shock tube is a non-contact approach to increase pressure amplitude by an order of magnitude for removal of particles without damaging the substrate through shockwave and LIP radiation heating effects. Heat transfer to the substrate increases as the distance from the LIP core to the substrate (gap distance d) decreases. LIP shockwaves in air, however, demonstrate a pressure decrease on an order of magnitude per every 5 mm in the reported experimental set-up. The shock tube technique allows for higher pressures at distances significantly further from the core of LIP. In the current investigation, the effect of a set of shock tubes to amplify the transient pressure of the LIP-generated shockwave fronts has been studied to evaluate their pressure amplification performances. The effectiveness of a shock tube is quantified in terms of its pressure amplification factor. Through experimental data from several shock tube geometries examined, pressure amplification factors of 11.00 have been experimentally verified which is a ratio of shock-tube-generated transient pressure of 523 kPa to in-air LIP transient pressure of 47.5 kPa at the same gap distance d = 10 mm. The potential advantages of shock tubes as an amplification approach are discussed.

Underwater amplification of laser-induced plasma (LIP)-generated transient pressure waves using shock tubes is introduced and demonstrated. Previously, it has been shown that LIP for noncontact particle removal is possible on the sub-100-nm level. This is now enhanced through shock tube utilization in a medium such as water by substantially increasing shock wave pressure for the same pulse energy. A shock tube constrains the volume and changes the propagation direction of the expanding plasma core by focusing a pulsed-laser beam inside a tube with a blind end, thus increasing the wave front pressure generated. Current amplification approach can reduce radiation exposure of the substrate from the shock wave because of the increased distance from the LIP core to the substrate provided by the increased pressure per unit pulse energy. For the same pulsed laser, with the aid of a shock tube, substantial levels of pressure amplitude amplification (8.95) and maximum pressure (6.48MPa) are observed and reported.