Hua C, Tennant D A, Savici A T, Sedov V, Sala G, Winn B
Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.
Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA.
Rev Sci Instrum. 2024 Mar 1;95(3). doi: 10.1063/5.0181310.
Knowledge about nonequilibrium dynamics in spin systems is of great importance to both fundamental science and technological applications. Inelastic neutron scattering (INS) is an indispensable tool to study spin excitations in complex magnetic materials. However, conventional INS spectrometers currently only perform steady-state measurements and probe averaged properties over many collision events between spin excitations in thermodynamic equilibrium, while the exact picture of re-equilibration of these excitations remains unknown. In this paper, we report on the design and implementation of a time-resolved laser-neutron pump-probe capability at hybrid spectrometer (beamline 14-B) at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory. This capability allows us to excite out-of-equilibrium magnons with a nanosecond pulsed laser source and probe the resulting dynamics using INS. Here, we discussed technical aspects to implement such a capability in a neutron beamline, including choices of suitable neutron instrumentation and material systems, laser excitation scheme, experimental configurations, and relevant firmware and software development to allow for time-synchronized pump-probe measurements. We demonstrated that the laser-induced nonequilibrium structure factor is able to be resolved by INS in a quantum magnet. The method developed in this work will provide SNS with advanced capabilities for performing out-of-equilibrium measurements, opening up an entirely new research direction to study out-of-equilibrium phenomena using neutrons.
了解自旋系统中的非平衡动力学对基础科学和技术应用都非常重要。非弹性中子散射（INS）是研究复杂磁性材料中自旋激发的不可或缺的工具。然而，传统的INS光谱仪目前仅进行稳态测量，并探测热力学平衡中自旋激发之间多次碰撞事件的平均性质，而这些激发重新达到平衡的确切情况仍然未知。在本文中，我们报告了在橡树岭国家实验室散裂中子源（SNS）的混合光谱仪（14-B束线）上设计和实现时间分辨激光-中子泵浦-探测功能。这种功能使我们能够用纳秒脉冲激光源激发非平衡磁振子，并使用INS探测由此产生的动力学。在这里，我们讨论了在中子束线中实现这种功能的技术方面，包括合适的中子仪器和材料系统的选择、激光激发方案、实验配置以及相关固件和软件开发，以实现时间同步的泵浦-探测测量。我们证明了激光诱导的非平衡结构因子能够通过INS在量子磁体中得到解析。这项工作中开发的方法将为SNS提供进行非平衡测量的先进能力，为利用中子研究非平衡现象开辟一个全新的研究方向。
