Second harmonic generation and third harmonic enhancement in silicon by composite metasurface and intense terahertz

In this work, a composite metasurface consisting of hollow-bow-tie-shaped metal metasurface and patterned amorphous silicon metasurface is proposed. An external terahertz (THz) electric field enhanced by the hollow-bow-tie structure is employed to break the centrosymmtry which allows the generation of optical second harmonic.

Meanwhile, the amorphous silicon nanocolumns inside the hollow-bow-tie-shaped structure enhances the optical laser field and improves the conversion efficiency of second and third harmonics. The numerical results indicate that at an incident optical laser intensity of 1.20 GW/cm2 and a y-component of the incident THz electric field of 10 kV/cm, the powers of the generated second and third harmonics are 3.96×10-6 W and 7.42×10-6 W, respectively, with conversion efficiencies of 3.93×10-7 and 7.18×10-7.