Optical emission of graphene and electron-hole pair production induced by a strong THz field

TL;DR

This study demonstrates the first experimental observation of optical emission from graphene induced by intense THz pulses, revealing electron-hole pair production via Landau-Zener transitions in heavily doped graphene.

Contribution

First experimental detection of graphene optical emission caused by strong THz fields, confirming theoretical predictions of Landau-Zener interband transitions in doped graphene.

Findings

Optical emission observed when THz field exceeds 100 kV/cm

Photon emission increases with field strength without heating effects

Experimental results agree with Landau-Zener transition theory

Abstract

We report on the first experimental observation of graphene optical emission induced by the intense THz pulse. P-doped CVD graphene with the initial Fermi energy of about 200 meV was used, optical photons was detected in the wavelength range of 340-600 nm. Emission started when THz field amplitude exceeded 100 kV/cm. For THz fields from 200 to 300 kV/cm the temperature of optical radiation was constant, while the number of emitted photons increased several dozen times. This fact clearly indicates multiplication of electron-hole pairs induced by an external field itself and not due to electron heating. The experimental data are in a good agreement with the theory of Landau-Zener interband transitions. It is shown theoretically that Landau-Zener transitions are possible even in the case of heavily doped graphene because the strong THz field removes quasiparticles from the region of interband transitions during several femtoseconds, which cancels the Pauli blocking effect.