Few cycle pulse laser ablation study of single layer TiO₂ thin films using time resolved surface microscopy.

Area of Science:

• Laser-matter interactions
• Materials science
• Non-linear optics

Background:

• Few cycle pulse (FCP) laser interactions with solids are crucial for advanced optics and optoelectronics.
• Understanding FCP laser damage and ablation mechanisms in solids and thin films remains limited.
• Existing research often uses longer pulses, leaving a gap in knowledge for ultra-short pulse dynamics.

Purpose of the Study:

• To systematically investigate the dynamics of FCP laser ablation in single-layer TiO2 thin films.
• To analyze the influence of film thickness and internal electric field distribution on ablation crater morphology.
• To elucidate the role of free carrier generation in FCP laser ablation processes.

Main Methods:

• Utilized time-resolved surface microscopy (TRSM) to observe ablation dynamics from 1 ps to 10 ns after a 9 fs laser pulse.
• Employed one-dimensional finite-difference time-domain (FDTD) simulations incorporating strong field ionization and free carrier absorption.
• Correlated TRSM observations with FDTD simulation results to estimate excited free carrier densities and propose ablation mechanisms.

Main Results:

• Observed distinct ablation crater features for FCPs compared to longer pulses (50-150 fs) at similar fluences.
• Demonstrated that FCP ablation dynamics are strongly influenced by thickness-dependent electric field distributions (λ/2 vs λ/4).
• Identified potential significant roles for free carrier generation via strong field ionization in the ablation process.

Conclusions:

• FCP laser ablation of TiO2 thin films exhibits unique characteristics tied to internal field distributions and free carrier dynamics.
• The study provides a mechanism explaining differences in ablation craters based on film thickness and laser-matter interactions.
• Findings contribute to the fundamental understanding of extreme non-linearities and inform the design of next-generation optical components.