Influence of distance between sample surface and focal point on the expansion dynamics of laser-induced silicon plasma under different sample temperatures in air

In this paper, we explored the influence of distance between sample surface and focal point on the expansion dynamics of laser-induced plasma under different sample temperatures in air. A Nd:YAG nanosecond pulse laser was used to ablate silicon and produce plasma plume. Using fast photography technology, we captured the images of the plasma plumes at different focusing positions and sample temperatures. During the expansion of plasma plume, with the decrease of the distance between focal point and sample surface, the emission intensity of the plasma increased first, and then dropped. In addition, the increase in the sample temperature could improve the expansion velocity of the plasma plume. Moreover, higher laser energy and sample temperatures could enhance the emission intensity and increase the plasma lifetime.