Interplay of pulse duration, peak intensity, and particle size in laser-driven electron emission from silica nanospheres

TL;DR

This study systematically investigates how particle size and laser parameters influence electron emission from silica nanospheres, revealing size-dependent energy scaling and enhanced electron energies in larger nanoparticles due to near-field effects.

Contribution

It introduces an experimental technique to reduce focal volume effects and demonstrates size-dependent electron energy scaling, highlighting the role of near-field localization in large nanoparticles.

Findings

Photoelectron energy increases with particle size, up to sixfold.

Large nanoparticles emit electrons with energies up to 200 times the ponderomotive energy.

Size and near-field effects significantly influence electron emission dynamics.

Abstract

We present the results of a systematic study of photoelectron emission from gasphase dielectric nanoparticles (SiO2) irradiated by intense 25 fs, 780 nm linearly polarized laser pulses as a function of particle size (20 nm to 750 nm in diameter) and laser intensity. We also introduce an experimental technique to reduce the effects of focal volume averaging. The highest photoelectron energies show a strong size dependence, increasing by a factor of six over the range of particles sizes studied at a fixed intensity. For smaller particle sizes (up to 200 nm), our findings agree well with earlier results obtained with few-cycle, ~4 fs pulses. For large nanoparticles, which exhibit stronger near-field localization due to field-propagation effects, we observe the emission of much more energetic electrons, reaching energies up to ~200 times the ponderomotive energy. This strong deviation in maximum photoelectron energy is attributed to the increase in ionization and charge interaction for many-cycle pulses at similar intensities.