Terahertz surface plasmons in optically pumped graphene structures

TL;DR

This paper investigates how optically pumped graphene structures can support amplified terahertz surface plasmons due to negative dynamic conductivity, with implications for graphene-based THz lasers.

Contribution

It demonstrates the conditions under which surface plasmons in graphene can be amplified in the terahertz range, highlighting the role of multiple layers and optical pumping.

Findings

Negative real part of dynamic conductivity enables SP amplification.

SP gain can substantially exceed that of dielectric waveguide structures.

Optimal number of graphene layers maximizes SP gain.

Abstract

We analyze the surface plasmons (SPs) propagating along the optically pumped single-graphene layer (SGL) and multiple-graphene layer (MGL) structures. It is shown that at sufficiently strong optical pumping when the real part of dynamic conductivity of SGL and MGL structures becomes negative in the terahertz (THz) range of frequencies due to the interband population inversion, the damping of the THz SPs can give way to their amplification. This effect can be used in graphene-based THz lasers and other devices. Due to relatively small SP group velocity, the absolute value of their absorption coefficient (SP gain) can be large, substantially exceeding that of the optically pumped structures with the dielectric waveguide. The comparison of the SGL and MGL structures shows that to maximize the SP gain the number of GL layers should be properly choosen.