Dynamic imaging of femtosecond laser ablation plume by using laser-generated soft X-ray

Abstract

Femtosecond laser ablation has attracted a lot of attention as a unique technique for the precise micromachining of solid surfaces and transparent materials, the synthesis of novel materials, and high-quality thin film growth in laser-processing technology [1]. The wide variety of applications of femtosecond laser ablation to laser-processing technology has stimulated interest in a comprehensive understanding of ablation dynamics, in particular the ejection and expansion dynamics of ablated particles in the ablation plume during the initial stage of femtosecond laser ablation. This is because ablation dynamics is important both for fundamental physics and for the high-level control of these processes. One of the most promising ways of studying the initial dynamics of femtosecond laser ablation is time-resolved x-ray absorption fine structure (TR-XAFS) spectroscopy, where a femtosecond laser pulse induces the ablation process and an x-ray pulse probes the ablation plume with picosecond or femtosecond temporal resolution. Since XAFS provides information on the local electronic state, which is sensitive to a chemical bonding or a local atomic structure, TR-XAFS has the potential to become a powerful tool for investigating a laser ablation process where phase transformation, bond breaking, and particle ejection occur instantaneously. In addition, another feature of the laser ablation process is the significant spatial dependence of the ejection of ablation particles. This convinces us that a spatiotemporally resolved XAFS (STR-XAFS) with high temporal and spatial resolution is preferable for performing detailed measurements of an expanding ablation plume.