抄録
Carrier-envelope phase-stable, femtosecond intense light sources in the mid-IR region are developed to
produce high harmonics in solids. Using these light sources, high harmonics are produced in GaSe.
Polarization analysis along with a first-principle simulation suggests that the intraband current is the primary
source for lower-order odd harmonics, which show unusual 30-degree periodicity. High harmonic
generation with circularly polarized electric field is also investigated. The selection rule for circularly
polarized high harmonics is experimentally confirmed for the first time.
