関西光科学研究所　|　第71回KPSIセミナー 「奇数」高調波– 4ステップモデルによる高調波とテラヘルツ高調波

関西光科学研究所 >> KPSIセミナー >> 「奇数」高調波– 4ステップモデルによる高調波とテラヘルツ高調波

セミナー

第71回KPSIセミナー

「奇数」高調波– 4ステップモデルによる高調波とテラヘルツ高調波

High-order harmonic generation (HHG) is an excellent tabletop source of coherent extreme ultraviolet and soft X-ray radiation. Since high-order harmonics are intrinsically generated in attosecond bursts, it is also opening a new domain of attosecond science. More recently, high-harmonic spectroscopy is evolving to become a unique tool for studying the electronic structure of atoms and molecules. The HHG process from most nonlinear media is well explained by the three-step model. In this talk, I will describe two “odd” cases where the three-step model does not apply. In the first example, I will describe our works on resonant harmonics, where the intensity of a specific harmonic order is more than 100 times higher than the other harmonics. I will show that such harmonics could be well explained by a four-step model, adding an extra step to the conventional three-step model. Such resonant harmonics are also leading to the observation of new phenomena, such as the generation of harmonics involving dressed autoionizing states.

In a second example, I will describe our works on high-order harmonic generation of intense, few-cycle terahertz (THz) pulses. I will show that THz harmonics could be explained by abandoning the microscopic picture, and adopting a macroscopic picture where the current in the nonlinear medium (in our case, n-doped semiconductor) generated by the intense THz pulse undergoes subcycle modulations, thus leading to harmonics. Such effects may be of interest for characterizing various materials for use in the sub-THz to THz frequencies (such as in future 6G devices).

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第72回KPSIセミナー　量子レベルでの「光子渦」の生成と検出