超高速電子が予期せぬ光信号を明らかにする（Ultrafast electrons reveal unexpected optical signal）

2026-09-03 スタンフォード大学

＜関連情報＞

• https://news.stanford.edu/stories/2026/09/ultrafast-electrons-optical-response-sensing-imaging
• https://www.nature.com/articles/s41566-026-01894-3

半導体中のメガ電子ボルト電子による強力な超高速非線形光学応答 Strong ultrafast nonlinear optical response from megaelectronvolt electrons in semiconductors

D. Jeong,T. R. Hopper,Y. Kim,X. Shen,P. L. Kramer,M. C. Hoffmann,R. Coffee,M. Fejer,A. M. Lindenberg & C. S. Levin
Nature Photonics  Published:20 April 2026
DOI:https://doi.org/10.1038/s41566-026-01894-3

Abstract

Understanding radiation–matter interactions on ultrafast timescales is essential for radiation detection technologies, particularly those requiring precise timing, such as plasma monitoring, synchrotron diagnostics and medical imaging. However, the detection of highly ionizing radiation is challenging due to the stochastic nature of the interactions, resulting in dispersed energy deposition. Here we show a nonlinear optical response in semiconductors induced by 150-fs, 4.2-MeV electrons that generate highly localized charge carriers. The induced sub-10-ps optical modulation reached up to 24.5%, accompanied by a blueshift in the absorption edge consistent with band filling and carrier densities of 10¹⁸cm⁻³. These carrier densities are 100-fold higher than expected from the deposited energy, indicating the extreme spatial localization of carriers at inelastic collisions along the ionization trajectories, thereby leading to the observed modulation. The strong nonlinearity of the MeV-electron-induced optical response enables the precise spatiotemporal detection of ionizing radiation at room temperature using common semiconductors and laser systems.