| 报告人简介 | Hrvoje Petek教授1980年和1985年分别在麻省理工学院与加州大学伯克利分校获得学士与博士学位，之后在日本分子科学研究所（1985 - 1993）和日立高等研究中心（1993 - 2000）工作，2000年加入匹兹堡大学物理与天文学系，并担任R. K. Mellon 讲席教授至今。他的研究兴趣涉及固体表面的超快光谱学、显微镜和飞秒化学。他开创了飞秒时间和纳米空间相干电子动力学的超快多光子光电发射谱研究。他获得的荣誉包括Alexander von Humboldt Research Award (2000), Morino Award (2014), Ahmed Zewail Award in Ultrafast Science and Technology (2019)等，并入选美国物理学会（APS）以及美国科学与艺术学会（AAAS）会士。 |
报告摘要 | When illuminated by light, free electrons in a metal screen the applied optical field by inducing the screening charge density on the Fermi screening length scale. We consider the screening response of free electrons to an incoming optical field. They are commonly described by a theoretical cartoon but never quantitatively examined in the process of screening. We perform two photon photoemission spectroscopy as a function of the optical field strength on attosecond time scale projecting the coherently responding electrons into the photoemission continuum for electron energy, momentum, and time analysis.1 The photoemission spectra of silver in the near-UV region show a field strength-dependent transformation from Bloch bands intoadelocalizedelectrondistribution thathaslost characterofthesingleparticlebandstructure of silver. The optical field appears to induce a phase transition from a lattice-periodic band structure to a correlated photon-electron state. Interferometric measurements show that the optical field dressed state appears and decays on sub-optical cycle, attosecond time scale. Spectroscopic evidence shows a significant role of the A2 ponderomotive/diamagnetic response of the electronic system, where A is the electromagnetic vector potential.
This is a work in progress, and your thought are welcome.
[1] M. Aeschlimann et al., Time-resolved photoelectron spectroscopy at surfaces, Surface Science 753, 122631 (2024). 10.1016/j.su
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