|日 時||2023年02月10日(金) 16:00|
Recent development of femtosecond mid-infrared laser has been promoting nonlinear optics in solids to enter an extreme regime, where light-matter interaction energy (or Rabi frequency) becomes comparable with the scale of electronic transition energy. Higher-order harmonic generation (HHG) is a typical extreme nonlinear optics in solids, where electron-hole pairs are coherently generated in solids via tunneling process. The phenomenon is nothing but the breaking the electronic vacuum in solids via Schwinger mechanism. This has opened a new platform for investigating the ultrafast electron dynamics in the multi-terahertz region, because it clearly reflects the electron motion driven by the intense sub-cycle laser fields. In this talk, we will show HHG spectra in several low dimensional materials which have different conductive properties, including metals. In metals, a simple intraband current model reproduces the experimental data well. We also show a photo-doping and electro-doping effects on HHG. Common features and individual aspects will be discussed.