High-Field High-Repetition-Rate Sources for the Coherent THz Control of Matter

Abstract

Ultrashort flashes of THz light with low photon energies of a few meV, but strong electric or magnetic field transients have recently been employed to prepare various fascinating nonequilibrium states in matter. Here we present a new class of sources based on superradiant enhancement of radiation from relativistic electron bunches in a compact electron accelerator that we believe will revolutionize experiments in this field. Our prototype source generates high-field THz pulses at unprecedented quasi-continuous-wave repetition rates up to the MHz regime. We demonstrate parameters that exceed state-of-the-art laser-based sources by more than 2 orders of magnitude. The peak fields and the repetition rates are highly scalable and once fully operational this type of sources will routinely provide 1 MV/cm electric fields and 0.3 T magnetic fields at repetition rates of few 100 kHz. We benchmark the unique properties by performing a resonant coherent THz control experiment with few 10 fs resolution.

Aligned copper nanorod arrays for highly efficient generation of intense ultra-broadband THz pulses

“…THz pulses with more than 100 MV/cm peak electric field have been demonstrated by difference-frequency mixing of two parametrically amplified pulses14. Electron accelerators can also be used to produce energetic THz pulses either (i) by bending a beam of relativistic electrons using a strong magnetic field or (ii) by sending them through a thin metal foil, but usually they are not available at modest laboratory scales15161718. Progress in research up to now has made it clear that many laser-based methods possess an upper limit in the maximum driving laser intensity19 that could be used, which is limiting the THz yield and hence their applications to several spectroscopic purposes420.…”

Light control of orbital domains: case of the prototypical manganite La0.5Sr1.5MnO4

“…This mechanism has a great promise for rapid contactless domain control. Further experiments with carrier-envelope phase stable, high-field multi-cycle THz pulses and sub-cycle time-resolution will unravel the fundamental timescale of the alignment process 30 .…”

Narrow-band tunable terahertz emission from ferrimagnetic Mn3-xGa thin films

“…22 We were able to drive the same mode in the Mn 3 Ga film selectively by resonant THz excitation. The spectral densities, orders of magnitude higher than those available from tabletop sources, 23 made it possible to detect the minute Faraday rotation signal (green solid line, Fig. 2(c)).…”

“…The phase shift between the two is 180 , proving their magnetic origin. Also shown in (c) is a Faraday measurement of the resonance driven by direct THz excitation with an intense quasi-cw narrow-band THz source 23 (green solid line).…”

“…To this end, direct, selective, coherent THz excitation of the fundamental magnetic resonances may be a crucial next development. 5,22,23 See supplementary material for more detailed information on: (i) the theoretical description of the ferrimagnetic system by means of two exchange coupled ferromagnetic sub-lattices and (ii) the analysis of the experimentally derived THz emission data. …”