Nonadiabatic Nano-optical Tunneling of Photoelectrons in Plasmonic Near-Fields

Nanoplasmonic Photoelectron Rescattering in the Multiphoton-Induced Emission Regime

In strong-field laser-matter interactions, energetic electrons can be created by photoemission and a subsequent rescattering and can attain energy as much as 10 times the ponderomotive potential (U_{p}) of the laser field. Here, we show that with the unique combination of infrared laser sources (exploiting the quadratic scaling of U_{p}) and plasmonic nanoemitters (which enhance rescattering probability by orders of magnitude) ∼10U_{p} rescattered electrons can be observed in the multiphoton-induced regime. Our experiments correspond well to a model based on the time dependent Schrödinger equation and allowed us to reveal an unexpected aspect of ultrafast electron dynamics in the multiphoton emission regime.

Analytical Model of Optical-Field-Driven Subcycle Electron Tunneling Pulses from Two-Dimensional Materials

We develop analytical models of optical-field-driven electron tunneling from the edge and surface of free-standing two-dimensional (2D) materials. We discover a universal scaling between the tunneling current density (J) and the electric field near the barrier (F): In(J/|F|β) ∝ 1/|F| with β values of 3/2 and 1 for edge emission and vertical surface emission, respectively. At ultrahigh values of F, the current density exhibits an unexpected high-field saturation effect due to the reduced dimensionality of the 2D material, which is absent in the traditional bulk material. Our calculation reveals the dc bias as an efficient method for modulating the optical-field tunneling subcycle emission characteristics. Importantly, our model is in excellent agreement with a recent experiment on graphene. Our results offer a useful framework for understanding optical-field tunneling emission from 2D materials, which are helpful for the development of optoelectronics and emerging petahertz vacuum nanoelectronics.

Carrier-envelope phase on-chip scanner and control of laser beams

The carrier-envelope phase (CEP) is an important property of few-cycle laser pulses, allowing for light field control of electronic processes during laser-matter interactions. Thus, the measurement and control of CEP is essential for applications of few-cycle lasers. Currently, there is no robust method for measuring the non-trivial spatial CEP distribution of few-cycle laser pulses. Here, we demonstrate a compact on-chip, ambient-air, CEP scanning probe with 0.1 µm3 resolution based on optical driving of CEP-sensitive ultrafast currents in a metal-dielectric heterostructure. We successfully apply the probe to obtain a 3D map of spatial changes of CEP in the vicinity of an oscillator beam focus with pulses as weak as 1 nJ. We also demonstrate CEP control in the focal volume with a spatial light modulator so that arbitrary spatial CEP sculpting could be realized.