Strong-Field Emission from Dielectric Nanoparticles

We extended our recently developed model for strong-field photoelectron (PE) emission from metal nanoparticles (NPs) driven by short infrared (IR) laser pulses to dielectric NPs. The extended theory follows the three-step framework introduced in Refs. [1,2], but requires a major revision of the first (ionization) step: instead of a Fowler–Nordheim (FN) tunneling description, we employ an ADK–PPT–type strong-field ionization rate [3] that more realistically captures valence-band electron emission in dielectrics by including both tunneling and multiphoton ionization. The ionization rate is implemented with a dynamic ionization potential that, importantly, incorporates the IR Stark shift and an additional Coulomb shift in work function due to the charge build-up on the NP. With these modifications, the model reproduces measured PE momentum distributions and cutoff energies [4]. We measured and simulated the wavelength dependence of the PE cutoff energy for NP diameters from 10 to 200 nm and peak intensities between 8.0×10¹² and 1.8×10¹³ W/cm². For amorphous silica nanospheres, the simulated cutoff energies agree well with experiment and reveal a pronounced departure from atomic strong-field emission: the dielectric NP cutoff decreases as the wavelength increases, in contrast to the well-known 10U_p cutoff energy of gaseous atomic targets [5].