Multifunctional Ionic-Gated Graphene Salisbury Mirror Supercapacitor, with Saturable Absorption, Amplitude Modulation and Frequency-Tuning Capabilities in the 2-5 THz Range

We report an electrolyte-gated single layer graphene super-capacitor, embedded in a polyethylene-on-Au Salisbury mirror optical architecture, working as a THz frequency modulator. The gate-tunable single layer graphene in a quarter wave waveguide ensures 40% optical amplitude modulation depth, and saturable absorption mirror operation, with $\sim 4.5 Wcm^{\mathbf{-2}}$ saturation intensity. By coupling the modulator with a THz quantum cascade laser frequency comb in an external cavity configuration, we also demonstrate fine-tuning of the intermode beatnote frequency, revealing a promising perspective for metrological sources requiring a tight frequency control of the intermode comb frequency