Optical Frequency Combs from High-Order Sideband Generation

TL;DR

This paper demonstrates the generation of optical frequency combs using high-order sideband generation in GaAs/AlGaAs quantum wells driven by intense THz fields, achieving spans over 80 THz and showcasing potential for precise THz source characterization.

Contribution

It introduces a novel method of creating broad optical frequency combs via high-order sideband generation in semiconductor quantum wells driven by high-intensity THz fields.

Findings

Frequency combs with over 120 sidebands were generated.

Comb spans exceeded 80 THz.

The comb characteristics depend on the product of THz frequency and field strength.

Abstract

We report on the generation of frequency combs from the recently-discovered phenomenon of high-order sideband generation (HSG). A near-band gap continuous-wave (cw) laser with frequency $f_\text{NIR}$ was transmitted through an epitaxial layer containing GaAs/AlGaAs quantum wells that were driven by quasi-cw in-plane electric fields $F_\text{THz}$ between 4 and 50 kV/cm oscillating at frequencies $f_\text{THz}$ between 240 and 640 GHz. Frequency combs with teeth at $f_\text{sideband}=f_\text{NIR}+nf_\text{THz}$ ($n$ even) were produced, with maximum reported $n>120$, corresponding to a maximum comb span $>80$ THz. Comb spectra with the identical product $f_\text{THz}\times F_\text{THz}$ were found to have similar spans and shapes in most cases, as expected from the picture of HSG as a scattering-limited electron-hole recollision phenomenon. The HSG combs were used to measure the frequency and linewidth of our THz source as a demonstration of potential applications.