Field emission at terahertz frequencies: AC-tunneling and ultrafast carrier dynamics

G Herink,C Ropers,L Wimmer

doi:10.1088/1367-2630/16/12/123005

Abstract

We demonstrate ultrafast terahertz (THz) field emission from a tungsten nanotip enabled by local field enhancement. Characteristic electron spectra which result from acceleration in the THz near-field are found. Employing a dual frequency pump–probe scheme, we temporally resolve different nonlinear photoemission processes induced by coupling near-infrared (NIR) and THz pulses. In the order of increasing THz field strength, we observe THz streaking, THz-induced barrier reduction (Schottky effect) and THz field emission. At intense NIR-excitation, the THz field emission is used as an ultrashort, local probe of hot electron dynamics in the apex. A first application of this scheme indicates a decreased carrier cooling rate in the confined tip geometry. Summarizing the results at various excitation conditions, we present a comprehensive picture of the distinct regimes in ultrafast photoemission in the near- and far-infrared.

Highlights

Terahertz (THz) radiation with a photon energy of few millielectron-volts is commonly regarded as being non-ionizing, and finds widespread applications in imaging, sensing and spectroscopy [1,2,3]
We demonstrate THz field emission enabled by the high field enhancement at tungsten nanotips
The THz field strength is controlled by rotation of the BBO crystal (figure 2(g)), and the pulses are coupled into an high vacuum chamber (10−8 mbar range) through a 500 μm thick, Brewster-angled silicon window

Summary

Introduction

Terahertz (THz) radiation with a photon energy of few millielectron-volts (meV) is commonly regarded as being non-ionizing, and finds widespread applications in imaging, sensing and spectroscopy [1,2,3]. The linear fielddependence of the kinetic energy cutoff maps the THz focus (blue, figure 1(e)), whereas the corresponding electron yield (red) demonstrates a higher localization due to the tunneling nonlinearity [15]. Assisted by optical field enhancement at the tungsten tip [30], the short NIR-pulse generates photoelectrons localized to the apex [19, 27, 29, 31,32,33,34,35,36,37,38], which are accelerated in the momentary THz potential.

Results

Conclusion