Comparative study of ablation processes using femtosecond and nanosecond lasers

This study investigated the dynamic characteristics of ions emitted from materials subjected to short-pulsed laser interactions. To investigate the difference in ablation dynamics due to laser pulse irradiation with the same energy but different time scales, we developed a time-of-flight (TOF) mass spectrometer and analyzed the TOF ion profiles obtained by irradiating 180 fs 800 nm Ti:sapphire femtosecond laser and 1 ns 355 nm Nd:YAG nanosecond laser. The effects of incident laser interaction with CsI deposits were examined for laser pulse energies ranging from 400 to 1000 nJ, corresponding to laser intensities of 7.1 × 10¹¹–1.8 × 10¹² W/cm² for femtosecond lasers and 1.3–3.2 × 10⁸ W/cm² for nanosecond lasers. With an ion trajectory simulation incorporating a shifted Maxwell–Boltzmann initial velocity distribution and continuous ion emission, we analyzed the ion emission dynamics from the TOF profiles. Compared with nanosecond lasers, femtosecond lasers generated ions with higher initial velocities but lower temperatures. Under nanosecond laser irradiation, ion emission continued for tens of nanoseconds after the end of the laser pulse, and its duration increased with increasing laser pulse energy. However, no continuous emission occurred under femtosecond laser irradiation.