Timm Rohwer

All-optical three-dimensional electron pulse compression

We propose a method of compressing and focusing electron pulses to attosecond durations and sub-micrometer-dimensions using the optical ponderomotive force. Applications include ultrafast electron diffraction, flat electron beam creation, and free-electron-based coherent terahertz emission schemes.

Ultrafast manipulation of mirror domain walls in a charge density wave

Topological defects, potential information carriers, were written into and erased from a solid with femtosecond light pulses. Domain walls (DWs) are singularities in an ordered medium that often host exotic phenomena such as charge ordering, insulator-metal transition, or superconductivity. The ability to locally write and erase DWs is highly desirable, as it allows one to design material functionality by patterning DWs in specific configurations. We demonstrate such capability at room temperature in a charge density wave (CDW), a macroscopic condensate of electrons and phonons, in ultrathin 1T-TaS2. A single femtosecond light pulse is shown to locally inject or remove mirror DWs in the CDW condensate, with probabilities tunable by pulse energy and temperature. Using time-resolved electron diffraction, we are able to simultaneously track anti-synchronized CDW amplitude oscillations from both the lattice and the condensate, where photoinjected DWs lead to a red-shifted frequency. Our demonstration of reversible DW manipulation may pave new ways for engineering correlated material systems with light.

Evidence for topological defects in a photoinduced phase transition

Alfred Zong, ∗ Anshul Kogar, ∗ Ya-Qing Bie, Timm Rohwer, † Changmin Lee, Edoardo Baldini, Emre Ergeçen, Mehmet B. Yilmaz, Byron Freelon, ‡ Edbert J. Sie, § Hengyun Zhou, ¶ Joshua Straquadine, 3, 4 Philip Walmsley, 3, 4 Pavel E. Dolgirev, Alexander V. Rozhkov, 6 Ian R. Fisher, 3, 4 Pablo Jarillo-Herrero, Boris V. Fine, 7 and Nuh Gedik ∗∗ Massachusetts Institute of Technology, Department of Physics, Cambridge, MA 02139, USA. Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA 94305, USA. Department of Applied Physics, Stanford University, Stanford, CA 94305, USA. SIMES, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA. Skolkovo Institute of Technology, Skolkovo Innovation Center, 3 Nobel Street, Moscow, 143026, Russia. Institute for Theoretical and Applied Electrodynamics, Russian Academy of Sciences, Moscow, 125412, Russia. Institute for Theoretical Physics, University of Heidelberg, Philosophenweg 12, 69120 Heidelberg, Germany. (Dated: April 20, 2018)

All-optical, three-dimensional electron pulse compression

We propose a method of compressing and focusing electron pulses to attosecond durations and sub-micrometer-dimensions using the optical ponderomotive force. Applications include ultrafast electron diffraction, flat electron beam creation, and free-electron-based coherent terahertz emission schemes.