Laser-Metal Interaction with a Pulse Shorter than the Ion Period: Ablation Threshold, Electron Emission and Ion Explosion

The laser energy per unit surface, necessary to trigger material removal, decreases with the pulse shortening, becoming pulse-time independent in the sub-picosecond range. These pulses are shorter than the electron-to-ion energy transfer time and electronic heat conduction time, minimising the energy losses. Electrons receiving an energy larger than the threshold drag the ions off the surface in the mode of electrostatic ablation. We show that a pulse shorter than the ion period (Shorter-the-Limit (StL)) ejects conduction electrons with an energy larger than the work function (from a metal), leaving the bare ions immobile in a few atomic layers. Electron emission is followed by the bare ion's explosion, ablation, and THz radiation from the expanding plasma. We compare this phenomenon to the classic photo effect and nanocluster Coulomb explosions, and show differences and consider possibilities for detecting new modes of ablation experimentally via emitted THz radiation. We also consider the applications of high-precision nano-machining with this low intensity irradiation.

Automated summary

The minimum laser energy required for material removal decreases with decreasing pulse duration in the sub-picosecond range. These short pulses minimize energy losses by being shorter than the electron-to-ion energy transfer and electronic heat conduction times. When the pulse duration is shorter than the ion period, conduction electrons with energy higher than the work function expel ions off the surface, leaving behind a few atomic layers of bare ions. The emission of electrons is followed by the explosion, ablation, and THz radiation of the bare ions. We compare this phenomenon with the classical photo effect and nanocluster Coulomb explosions, discuss the differences, and explore the possibility of experimentally detecting new modes of ablation through emitted THz radiation. We also consider the application of high-precision nano-machining with low-intensity irradiation.