Abstract-Pulse- and field-resolved THz-diagnostics at 4𝑡ℎ generation lightsources

M. Chen, J.-C. Deinert, B. Green, Z. Wang, I. Ilyakov, N. Awari, M. Bawatna, S. Germanskiy, T. V. A. G. de Oliveira, G. Geloni, T. Tanikawa, M. Gensch, and S. Kovalev

Fig. 1. Experimental scheme: The setup has been installed and tested at the TELBE THz facility which consist of two superradiant THz sources: a CDR and an undulator. Two ATMs are employed: one detecting the CDR pulses and one detecting pulses from the undulator. Additional monitor based on fast pyroelectric detector measures the intensities of each undulator pulse. Sequential EO sampling serves as ultrafast benchmark experiment.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-22-32360

Multi-color pump-probe techniques utilizing modern accelerator-based 4th generation light sources such as X-ray free electron lasers or superradiant THz facilities have become important science drivers over the past 10 years. In this type of experiments the precise knowledge of the properties of the involved accelerator-based light pulses crucially determines the achievable sensitivity and temporal resolution. In this work we demonstrate and discuss the powerful role pulse- and field-resolved- detection of superradiant THz pulses can play for improving the precision of THz pump - femtosecond laser probe experiments at superradiant THz facilities in particular and at 4th generation light sources in general. The developed diagnostic scheme provides real-time information on the properties of individual pulses from multiple accelerator based THz sources and opens a robust way for sub femtosecond timing. Correlations between amplitude and phase of the pulses emitted from different superradiant THz sources furthermore provide insides into the properties of the driving electron bunches and is of general interest for the ultra-fast diagnostics at 4th generation light sources.

Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Abstract-Towards femtosecond-level intrinsic laser synchronization at fourth generation light sources

M. Chen, S. Kovalev, N. Awari, Z. Wang, S. Germanskiy, B. Green, J.-C. Deinert, and M. Gensch

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-43-9-2213

In this Letter, the proof of principle for a scheme providing intrinsic femtosecond-level synchronization between an external laser system and fourth generation light sources is presented. The scheme is applicable at any accelerator-based light source that is based on the generation of coherent radiation from ultrashort electron bunches such as superradiant terahertz (THz) facilities or X-FELs. It makes use of a superradiant THz pulse generated by the accelerator as an intrinsically synchronized gate signal for electro-optical slicing. We demonstrate that the scheme enables a reduction of the timing instability by more than 2 orders of magnitude. This demonstration experiment thereby proves that intrinsically synchronized time-resolved experiments utilizing laser and accelerator-based radiation pulses on few tens of femtosecond (fs) to few fs timescales are feasible.

© 2018 Optical Society of America

Abstract-Magnetic Excitations and Continuum of a Field-Induced Quantum Spin Liquid in α-RuCl3

Zhe Wang, S. Reschke, D. Hüvonen, S.-H. Do, K.-Y. Choi, M. Gensch, U. Nage, T. Rõõm, A. Loidl

(Submitted on 19 Jun 2017)

https://arxiv.org/abs/1706.06157

We report on terahertz spectroscopy of quantum spin dynamics in α-RuCl3, a system proximate to the Kitaev honeycomb model, as a function of temperature and magnetic field. An extended magnetic continuum develops below the structural phase transition at Ts2=62K. With the onset of a long-range magnetic order at TN=6.5K, spectral weight is transferred to a well-defined magnetic excitation at ℏω1=2.48meV, which is accompanied by a higher-energy band at ℏω2=6.48meV. Both excitations soften in magnetic field, signaling a quantum phase transition at Bc=7T where we find a broad continuum dominating the dynamical response. Above Bc, the long-range order is suppressed, and on top of the continuum, various emergent magnetic excitations evolve. These excitations follow clear selection rules and exhibit distinct field dependencies, characterizing the dynamical properties of the field-induced quantum spin liquid.