Comparative study of ablation processes using femtosecond and nanosecond lasers

• Femtosecond and nanosecond lasers induce fundamentally different ablation mechanisms. • A time-of-flight mass spectrometer was developed for ion dynamics analysis. • A continuous ion emission model was developed to reproduce the ion time-of-flight profile well. • Nanosecond laser generates hot, slow ions emitted over a prolonged duration. • Femtosecond laser generates cold, fast ions emitted instantaneously. 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 × 10 11 –1.8 × 10 12 W/cm 2 for femtosecond lasers and 1.3–3.2 × 10 8 W/cm 2 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.