报告人：陶镇生 教授 复旦大学   

主持人：蒋士成 副研究员   

时间：2022年10月28日（周五）上午10:00   

地点：腾讯会议ID: 697-317-057    

报告人简介：

陶镇生教授，2005年和2008年获得复旦大学物理学系学士和硕士学位，2014年在美国密歇根州立大学物理天文系获得博士学位。2014-2018年在美国JILA，科罗拉多博德分校，Kapteyn-Murnane组任博士后助理研究员，2018年至今在复旦大学物理学系任研究员，博士生导师。主要兴趣在研究光与物质相互作用（特别是强光场条件下）的超快物理过程，发展新型超快光学技术。

报告内容简介：

Extending the photon energy range of bright high-harmonic generation to cover the entire soft X-ray region is important for many applications in science and technology. The concept of critical ionization fraction has been essential, because it dictates the maximum laser intensity that drives the harmonic emission while preserving the phase matching, so that it is sufficiently bright for routine applications in spectroscopy and imaging. In this work, we reveal a second, nonadiabatic critical ionization fraction that can substantially extend the maximum phase-matched high-harmonic photon energy, arising due to the strong reshaping of the intense driving laser field in a gas plasma. We validate this understanding through a systematic comparison between experiment and theory, for a wide range of pulse durations and driving laser wavelengths. In particular, the properties of the high-harmonic spectrum versus the intensity of a few-cycle pulse undergoes three distinctive scenarios: (i) coincidence with the single-atom cutoff, (ii) strong spectral extension and, (iii) spectral energy saturation. We also present an analytical model that predicts the spectral extension that can be achieved for different driving lasers. This reveals the increasing importance of nonadiabatic critical phase matching when driven by few-cycle mid-infrared lasers. These findings are important for the development of high-brightness soft X-ray sources for applications in spectroscopy and imaging.