We present measurements of the polarization dependencies of the x-ray signal photons generated by the effect of parametric down-conversion of x rays into ultraviolet radiation. The results exhibit pronounced discrepancies with the classical model for the nonlinearity but qualitatively agree with a newly developed quantum mechanical theory for the nonlinear interaction. Our work shows that the reconstruction of the atomic scale charge distribution of valence electrons in crystals by using nonlinear interaction between x rays and longer wavelength radiation, as was suggested in previous works, requires the knowledge of polarization of the generated x-ray signal beam. The results presented in this work indicate a new methodology for the study of properties of the Wannier functions in crystals.
High-Performance Quantum Frequency Conversion from Ultraviolet to Telecom Band
Hefei National Research Center for Physical Sciences at the Microscale（合肥微尺度物质科学国家研究中心）；School of Physical Sciences, University of Science and Technology of China（中国科学技术大学物理学院）；Jinan Institute of Quantum Technology（济南量子技术研究院）；CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China（中国科学技术大学中国科学院量子信息与量子物理前沿卓越创新中心）；Hefei National Laboratory（合肥国家实验室）
40% boost in extreme ultraviolet conversion efficiency via simultaneous dual-beam 2-μm laser irradiation
Utsunomiya University（宇都宫大学）；RIKEN Center for Advanced Photonics, RIKEN（理化学研究所先进光子学研究中心）；The University of Tokyo（东京大学）；Tohoku University（东北大学）；University College Dublin（都柏林大学学院）；Hiroshima University（广岛大学）
Record nonlinear conversion efficiency in the production of high spectral purity vacuum ultraviolet laser at 148 nm
IPG Photonics Corporation（IPG光子公司）；JILA, NIST and University of Colorado, Department of Physics, University of Colorado（JILA、美国国家标准与技术研究院和科罗拉多大学物理系，科罗拉多大学）；CREOL, The College of Optics and Photonics（CREOL光学与光电子学院）
Programmable spectral phase transfer to the ultraviolet by gas-filled-fibre four-wave mixing
University of California Los Angeles（加州大学洛杉矶分校）；SLAC National Accelerator Laboratory, Stanford University（斯坦福大学SLAC国家加速器实验室）；California NanoSystems Institute（加州纳米系统研究所）
Polarization-Sensitive Third Harmonic Generation in resonant silicon nitride Metasurfaces for deep-UV Emission
Universitat Politècnica de Catalunya（加泰罗尼亚理工大学）；Università degli Studi di Brescia（布雷西亚大学）；DTU Nanolab, National Center for Nanofabrication and Characterization（丹麦技术大学纳米实验室，国家纳米加工与表征中心）；DTU Electro, Department of Electrical and Photonics Engineering（丹麦技术大学电气与光子工程系）
