I. Introduction
TRONG-field photoemission of electrons has been extensively studied in the past [1, 2]. Enabled by the development of high-intensity THz sources, THz field driven emission from a nanotip [3] up to fC bunch charge [4], and with pC charge from an antenna structure [5] have been demonstrated. Field driven electron emission (FEE) process is exclusively the quantum mechanical effects which allows the tunneling of electrons into vacuum. This phenomena occurs in high electric fields of 107 – 108 V/cm (in optical wavelength regime). The high electric field narrows the potential barrier at the metal-vacuum interface sufficiently for the electrons to have a significant probability of tunneling from the solid into the vacuum.