@article{oai:repo.qst.go.jp:00080086,
 author = {佐成晏之 and 乙部, 智仁 and 金光義彦 and 廣理英基 and Otobe, Tomohito},
 journal = {Nature Communications},
 month = {Jun},
 note = {Frequency-mixing processes of optical fields in solids are very important for many nonlinear optics applications, e.g., sum/difference frequency generation, optical parametric generation, and four-wave mixing . The recent developments of strong mid-infrared and terahertz light pulses have allowed electrons to be driven into a region far from the band edge, leading to high-order harmonics generation (HHG) by the field-driven carriers in the band structure [2-9]. However, despite their vital importance to frequency-mixing applications and the band reconstruction methodology, an angular and polarization selection rule for frequency-mixing processes in HHG induced by two-color optical fields has not yet been studied. Here, we observed HHG from a bulk crystal GaSe excited by orthogonally polarized two-color laser fields. Good agreement between the observed angle dependence and an analytical formula derived by taking into account the two-dimensional electron motion indicates that the one optical field amplifies the intraband nonlinear current driven with the other field and enhances the high-order harmonics (HHs). Our results provide the selection rule for frequency-mixing processes deformed by strongly driven carriers, which may lead to new technologies for polarization control and waveform synthesis of HHs with ultra-broadband spectra.},
 pages = {3069-1--3069-7},
 title = {Modifying angular and polarization selection rules of high-order harmonics by controlling electron trajectories in k-space},
 volume = {11},
 year = {2020}
}