Ionization-Induced Subcycle Metallization of Nanoparticles in Few-Cycle Pulses

Abstract

Strong-field laser-matter interactions in nanoscale targets offer unique avenues for the generation and detailed characterization of matter under extreme conditions. Field-driven, subcycle ionization-induced metallization of nanoscale solids in intense laser fields has been predicted (Peltz et al. Time-Resolved X-ray Imaging of Anisotropic Nanoplasma Expansion. Phys. Rev. Lett. 2014, 113, 133401), but its observation was hampered by a lack of a smoking gun. Here, we report the ultrafast metallization of isolated dielectric and semiconducting nanoparticles under intense few-cycle laser pulses. The highest-energy electron emission is found to be a decisive proof that shows a characteristic cutoff modification to a metallic limit for intensities high enough to ignite carrier avalanching in the volume of the particles. Semiclassical Mean-field Mie Monte-Carlo transport simulations reveal the underlying dynamics and explain the observed evolution by near-field driven electron backscattering from the metallizing target.

Strong-field physics with nanospheres

“…In this section we will review selected work considering the photemission form spheres with metallic optical response. The onset of subscycle metallization of initially dielectric and semiconducting small nanospheres under intense few-cycle pulses has been reported by Liu et al [64], where the previous studies have been extended to even higher laser intensities. In particular, a systematic analysis of the cutoff energy of fast photoelectrons measured from SiO 2 particles in dependence of laser intensity revealed a rapid transition from the 50 U p scaling law observed earlier [36,41] around a transition intensity of I trans = 1.8 × 10 14 W/cm 2 followed by saturation around 100 U p (cf.…”

“…These effects can be accounted for in higher level descriptions such as the semi-classical Mie Mean-field Monte-Carlo (M 3 C) model [22,41,47] or via microscopic particle-in-cell (MicPic) models [62,63]. In the following, the details of M 3 C are discussed, as this method has been utilized in most of the scenarios presented in this review [41,43,44,[46][47][48]54,55,64] and was recently also extended for the description of strong-field ionization from metal nanotips [65].…”

“…In this case, the latter becomes larger that the geometrical cross section σ geo = n Transport and total cross section are compared in the top right inset. From [64] an modified energy-dependent effective transport cross section…”

“…The solid vertical line marks the effective ionization energy of SiO 2 .Transport and total cross section are compared in the top right inset. From[64]…”

Signatures of the Carrier Envelope Phase in Nonlinear Thomson Scattering

“…For the latter, the exact shape of the field is important, i.e., the phase of the oscillations with respect to the envelope (carrier envelope phase; φ cep ) and is therefore important to control in experiments. For intensities up to 10 14 -10 15 W/cm 2 , methods exist to measure φ cep by utilizing ionization processes [4][5][6][7]. In relativistic laser pulses, the carrier envelope phase cannot be distinguished through ionization; however, other light-matter interactions are susceptible to φ cep and could be utilized for measuring it.…”