Effects of excitation frequency on high-order terahertz sideband generation in semiconductors

Abstract

We theoretically investigate the effects of the excitation frequency on the plateau of high-order terahertz sideband generation (HSG) in semiconductors driven by intense terahertz (THz) fields. We find that the plateau of the sideband spectrum strongly depends on the detuning between the near-infrared laser field and the band gap. We use the quantum trajectory theory (three-step model) to understand the HSG. In the three-step model, an electron-hole pair is first excited by a weak laser, then driven by the strong THz field, and finally recombined to emit a photon with energy gain. When the laser is tuned below the band gap (negative detuning), the electron-hole generation is a virtual process that requires quantum tunneling to occur. When the energy gained by the electron-hole pair from the THz field is less than 3.17 times the ponderomotive energy (U p ), the electron and the hole can be driven to the same position and recombined without quantum tunneling, so that the HSG will have large probability amplitude. This leads to a plateau feature of the HSG spectrum with a high-frequency cutoff at about 3.17U p above the band gap. Such a plateau feature is similar to the case of high-order harmonics generation in 4

Enhancement of terahertz photoconductive antenna operation by optical nanoantennas

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Nanosecond-pulse-controlled higher-order sideband comb in a GaAs optomechanical disk resonator in the non-perturbative regime

“…The same typical spectral structure, plateau and cutoff, in both the HSG and HHG shows that the mechanical oscillator, which is a macroscopic object, may also exhibit phenomena which are similar to those in atoms, including non-perturbative effects. It should be noted that HSG has also been found in other systems, such as semiconductors [53], bulk GaAs [54], terahertz quantum cascade lasers [55], and transient lasing [56], however, with other mechanisms.…”