On vaporization in laser material interaction

Abstract

In this article, vaporization processes in the laser interaction with materials are studied theoretically and computationally, focusing on evaporation and homogeneous bubble nucleation. Simulations are carried out using the Redlich-Kwong equation of state and temperature-dependent material property models that can be used up to the critical point. From theoretical considerations, four important temperatures are identified in the understanding of laser material interaction. This study also shows that there are upper limits to the amount of energy that can be consumed by vaporization, which takes place at a temperature that is lower than the material's critical point. This study also discusses the transition from the thermal mode of ablation to the nonthermal mode in terms of the energy capacity of homogeneous boiling.

355, 532, and 1064 nm picosecond laser interaction with grass tissues

“…[5][6][7][8][9][10] Plant leaves, especially green leaves, are common landscaping and agricultural materials and lasers could be creatively used for many possible innovative applications. Plant leaves exhibit very complicated optical properties because they have complex multilayer structures and are basically a composite of many dissimilar optical elements, including photosynthesizing pigments.…”

CO2and Er:YAG laser interaction with grass tissues

“…It is well known that the evaporation pressure increases almost exponentially towards the critical point, and according to Ref. 20, the maximum attainable pressure by surface evaporation is estimated to be p % 0:333p cp % 74 bar at T % 0:924T c % 325 C, where the critical point pressure (p cp ) of water is 220.9 bar. 19 Meanwhile, homogeneous boiling is initiated at around T % 0:9T cp % 309 C, and the maximum achievable vaporization pressure could be close to p cp.…”

“…. 20 Considering that grass tissues are tender and the laser-induced pressure force acts impulsively, we may think that both vaporization modes contribute to the cutting of grass blades over a wide temperature range. However, since carbonization has a lower threshold energy density than the ablation of grass tissues as evidenced in Figure 6(a), we believe that the actual ablation occurs at a higher temperature than $320 C, meaning that the ablation is primarily by homogeneous boiling.…”

In situ optical observations of keyhole dynamics during laser drilling

“…[5][6][7][8][9][10][11][12] Multiple physical processes are involved in the millisecond laser drilling process which couples keyhole dynamics with melt flow, melt pool boiling, plasma generation inside the drilling hole, and melt droplet ejection and evaporation outside the drilling hole. [13][14][15][16][17][18] The complexity and intricacy of these processes pose an obstacle to a comprehensive understanding of keyhole instability and especially to explain its evolution.…”