Terahertz generation and amplification in graphene nanoribbons in multi-frequency electric fields

We study theoretically a multi-frequency response of electrons in confined graphene subject to DC-AC driven fields. We explore the possibility for using graphene nanoribbons (GNRs) to generate and amplify terahertz (THz) radiations in electric field domainless regime. We discover two main important schemes of generation; when the frequencies are commensurate, THz generation is due to wave mixing and when they are non-commensurate, a single strong field suppresses space charge instability and any weak signals can get amplified.