Electrically Tunable Nonequilibrium Optical Response of Graphene

Abstract

The ability to tune the optical response of a material via electrostatic gating is crucial for optoelectronic applications, such as electro-optic modulators, saturable absorbers, optical limiters, photodetectors, and transparent electrodes. The band structure of single layer graphene (SLG), with zero-gap, linearly dispersive conduction and valence bands, enables an easy control of the Fermi energy, E F , and of the threshold for interband optical absorption. Here, we report the tunability of the SLG nonequilibrium optical response in the near-infrared (1000–1700 nm/0.729–1.240 eV), exploring a range of E F from −650 to 250 meV by ionic liquid gating. As E F increases from the Dirac point to the threshold for Pauli blocking of interband absorption, we observe a slow-down of the photobleaching relaxation dynamics, which we attribute to the quenching of optical phonon emission from photoexcited charge carriers. For E F exceeding the Pauli blocking threshold, photobleaching eventually turns into photoinduced absorption, because the hot electrons’ excitation increases the SLG absorption. The ability to control both recovery time and sign of the nonequilibrium optical response by electrostatic gating makes SLG ideal for tunable saturable absorbers with controlled dynamics.

Ultrafast Terahertz Self-Induced Absorption and Phase Modulation on a Graphene-Based Thin Film Absorber

“…For this normalization we assumed E F,SLG ≈ 200 meV at CNP. The above value was determined after fitting the calculated spectra to experimental measurements under 1.4 V bias and is in line with previously reported values of graphene residual doping on ionic liquid substrates. ,, We observe a similar behavior with the experimental findings (see Figure ). As the THz field increases, so does the calculated reflectance, presenting also the characteristic red shift of the resonance observed in the experiment.…”

“…values of graphene residual doping on ionic liquid substrates. 18,31,51 We observe a similar behaviour with the experimental findings (see Fig. 3).…”

Nonlinear co-generation of graphene plasmons for optoelectronic logic operations

“…By increasing V D we drive a current in the graphene channel and shift E F towards the Dirac point and the upper Dirac cone (n-doping). The graphene’s resistance reaches the maximum (Dirac point) when V D = 0.16 V. We notice that it is experimentally impossible to achieve E F = 0 eV due to the presence of puddles and inhomogeneities 43 . However, for simplicity we define E F = 0 eV as the point where we measure the minimum conductivity in the GDF.…”

Measurement of ultrafast carrier dynamics in multilayer MPCVD graphene

“…Ultrafast time-resolved spectroscopy techniques, such as pump-probe, can be used to study photoinduced dynamical processes in materials and in nanostructures [1,2]. In pump-probe experiments, a first "strong" light pulse called pump promotes an electronically excited state.…”

“…Understanding the carrier dynamics of graphene on a substrate is fundamental for the development of graphene-based optoelectronic devices [3]. The study of the dynamics can also reveal the quality of graphene, since, for example, the amount of defects in graphene affects its cooling properties [1]. In this work, we present preliminary ultrafast degenerate pump-probe measurements of graphene coatings synthesized by MPCVD.…”