Abstract-Terahertz-based subfemtosecond metrology of relativistic electron beams

R. K. Li, M. C. Hoffmann, E. A. Nanni, S. H. Glenzer, M. E. Kozina, A. M. Lindenberg, B. K. Ofori-Okai, A. H. Reid, X. Shen, S. P. Weathersby, J. Yang, M. Zajac, and X. J. Wang

https://journals.aps.org/prab/abstract/10.1103/PhysRevAccelBeams.22.012803

We demonstrate single-shot temporal characterization of relativistic electron bunches using single-cycle terahertz (THz) field streaking. A transverse deflecting structure consisting of a metal slit enables efficient coupling of the THz field and electron bunch. The intrinsically stable carrier envelope phase and strong gradient of the THz pulses allow simultaneous, self-calibrated determination of the time-of-arrival with subfemtosecond precision and bunch duration with single-femtosecond precision, respectively, opening up new opportunities for ultrafast electron diffraction as well as accelerator technologies in general.

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Abstract-Terahertz-driven phonon upconversion in SrTiO3

M. Kozina, M. Fechner, P. Marsik, T. van Driel, J. M. Glownia, C. Bernhard, M. Radovic, D. Zhu, S. Bonetti, U. Staub,  M. C. Hoffmann,

https://www.nature.com/articles/s41567-018-0408-1

Direct manipulation of the atomic lattice using intense long-wavelength laser pulses has become a viable approach to create new states of matter in complex materials. Conventionally, a high-frequency vibrational mode is driven resonantly by a mid-infrared laser pulse and the lattice structure is modified through indirect coupling of this infrared-active phonon to other, lower-frequency lattice modulations. Here, we drive the lowest-frequency optical phonon in the prototypical transition metal oxide SrTiO3 well into the anharmonic regime with an intense terahertz field. We show that it is possible to transfer energy to higher-frequency phonon modes through nonlinear coupling. Our observations are carried out by directly mapping the lattice response to the coherent drive field with femtosecond X-ray pulses, enabling direct visualization of the atomic displacements.

Abstract-Terahertz-driven magnetism dynamics in the orthoferrite DyFeO3

A. H. M. Reid, Th. Rasing, R. V. Pisarev, H. A. Dürr, M. C. Hoffmann

(Submitted on 5 Jun 2017)

      https://arxiv.org/abs/1706.01545

Terahertz driven magnetization dynamics are explored in the orthoferrite DyFeO3. A high-field, single cycle THz pulse is used to excite magnon modes in the crystal together with other resonances. Both quasi-ferromagnetic and quasi-antiferromagnetic magnon modes are excited and appear in time-resolved measurements of the Faraday rotation. Other modes are also observed in the measurements of the time-resolved linear birefringence. Analysis of the excitation process reveals that despite larger than expected electro-optical susceptibility it is mainly the THz magnetic field that couples to the quasi-ferromagnetic and quasi-antiferromagnetic magnon branches.

Abstract-Local terahertz field enhancement for time-resolved x-ray diffraction

M. Kozina,  M. Pancaldi, C. Bernhard, T. van Driel, J. M. Glownia,   P. Marsik, M. Radovic, C. A. F. Vaz, D. Zhu,  S. Bonetti, U. Staub, M. C. Hoffmann

http://aip.scitation.org/doi/abs/10.1063/1.4977088

We report local field strength enhancement of single-cycle terahertz (THz) pulses in an ultrafast time-resolved x-ray diffraction experiment. We show that patterning the sample with gold microstructures increases the THz field without changing the THz pulse shape or drastically affecting the quality of the x-ray diffraction pattern. We find a five-fold increase in THz-induced x-ray diffraction intensity change in the presence of microstructures on a SrTiO3thin-film sample.

Abstract-Ultrafast X-ray pulse characterization at free-electron lasers

I. Grguraš, A. R. Maier, C. Behrens, T. Mazza, T. J. Kelly, P. Radcliffe, S. Düsterer, A. K. Kazansky, N. M. Kabachnik, Th. Tschentscher, J. T. Costello, M. Meyer, M. C. Hoffmann, H. Schlarb & A. L. Cavalieri

http://www.nature.com/nphoton/journal/v6/n12/full/nphoton.2012.276.html
The ability to fully characterize ultrashort, ultra-intense X-ray pulses at free-electron lasers (FELs) will be crucial in experiments ranging from single-molecule imaging to extreme-timescale X-ray science. This issue is especially important at current-generation FELs, which are primarily based on self-amplified spontaneous emission and radiate with parameters that fluctuate strongly from pulse to pulse. Using single-cycle terahertz pulses from an optical laser, we have extended the streaking techniques of attosecond metrology to measure the temporal profile of individual FEL pulses with 5 fs full-width at half-maximum accuracy, as well as their arrival on a time base synchronized to the external laser to within 6 fs r.m.s. Optical laser-driven terahertz streaking can be utilized at any X-ray photon energy and is non-invasive, allowing it to be incorporated into any pump–probe experiment, eventually characterizing pulses before and after interaction with most sample environments.