Theodor Secanell Holstad¹,Trygve Ræder¹,Erik Knudsen¹,Matt Seaberg²,Tim van Driel²,Bernard Kozioziemski³,Jon Eggert³,Eric Folsom³,Leora Dresselhaus-Marais^3,4,2,Martin Meedom Nielsen¹,Henning Poulsen¹,Hugh Simons¹,Kristoffer Haldrup¹

Technical University of Denmark¹,SLAC National Accelerator Laboratory²,Lawrence Livermore National Laboratory³,Stanford University⁴

Abstract

Technical University of Denmark¹,SLAC National Accelerator Laboratory²,Lawrence Livermore National Laboratory³,Stanford University⁴

During the last decade, Dark-Field X-ray Microscopy (DFXM) has emerged as a powerful tool for mapping the microstructure within bulk crystalline materials in three dimensions [1]. So far, this technique has been limited to a time resolution of about ~30 ms [2]. In this work, we implemented DFXM at an X-ray free-electron-laser (XFEL), the Linac Coherent Light Source at Stanford, using an optical-pump / X-ray-probe scheme. We used this setup to successfully image strain waves propagating deep within the bulk of mm-sized single-crystal diamonds with a ps temporal resolution. Two separate wave-packets were observed traversing the crystal with different velocities, corresponding to longitudinal and transverse phonon modes. Information about their velocity, attenuation and mean free path could thus directly be measured - key properties for diamond's massively high thermal conductivity. In outlook, by demonstrating a novel approach to observe ultrafast phonon dynamics in deeply embedded volumes, we open the door to direct visualization and understanding of a plethora of phenomena. We therefore anticipate that our findings will have a wide impact in the fields of materials physics and condensed matter science. References [1] H. Simons et al. Long-range symmetry breaking in embedded ferroelectrics. Nat. Mater. 17:814-819, 2018. [2] L. E. Dresselhaus-Cooper. An Ultrafast View of X-ray Induced Defect Dynamics in Cosmic Diamonds. PAL Experimental Report Form LLNL-TR-810542, 2020.