Amplification of Plasma at Different Initial Temperatures inside a Microhole by a Short Laser Pulse and the Effect on the Hole Sidewall

Microholes with diameters varying with the hole depth have promising applications in important applications, but their manufacturing is difficult when the diameter of the hole is very small and/or varies complicatedly with the depth. In the authors' previous work (Dabir-Moghaddam et al., 2016), physics-based modeling study has been carried out on the interaction of a short laser pulse with a plasma plume that pre-exists in a microhole and the resulted effect on the sidewall of the hole. The model calculations have implied that a novel dual-pulse laser ablation and plasma amplification (LAPA) technique is potentially feasible for drilling microholes with diameters that are different at different hole depths. In this paper, further model calculations have been performed to study the effect of different initial plasma temperatures. Under the studied conditions, it has been found that laser amplification of a plasma plume with a higher initial temperature can lead to a larger heat flux to the hole sidewall surface and a larger surface vaporization depth in the sidewall, which indicates that more significant material removal will be expected. On the other hand, a lower initial plasma temperature can lead to more non-uniform vaporization depths at different sidewall locations, indicating that a spatially more selective material removal will be expected.