Manipulating high-harmonic generation in single walled carbon nanotubes

High-harmonic generation (HHG), which is the generation of multiple optical harmonic light, is an unconventional nonlinear optical phenomenon beyond the perturbation regime. The HHG in solid state materials is strongly influenced by the presence of nonlinearity in transport and optical transitions, but how to engineer these parameters has not yet been elucidated. Here, we demonstrate manipulation of HHG by tuning the electronic structure and carrier densities using single-wall carbon nanotubes with tuned electronic structures and Fermi levels. We reveal systematic changes in the HH spectra of carbon nanotubes with a series of electronic structures from a zero band-gap metal to a semiconductor. We demonstrate enhancement or reduction of harmonic generation by more than one order of magnitude by tuning electron and hole injection into the semiconductor carbon nanotubes through static electric field application.