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-Characterization of a graphene-based terahertz hot-electron bolometer

H. Gao, W. Miao, Z. Wang, W. Zhang, Y. Geng, S. C. Shi, C. Yu, Z. Z. He, Q. B. Liu, Z. H, Feng

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10826/108260X/Characterization-of-a-graphene-based-terahertz-hot-electron-bolometer/10.1117/12.2500700.short?SSO=1

Graphene has an extremely weak coupling of electrons to phonons due to its nonionic character of lattice. This remarkable property makes graphene very attractive for hot electron bolometers (HEBs). In this paper, we present the development of a graphene-based terahertz hot electron bolometer (HEB) with Johnson noise readout. The HEB is essentially a graphene microbridge that is connected to a log spiral antenna by Au contact pads. We study the responsivity, noise equivalent power (NEP) and time constant of the graphene-based HEB in a perpendicular magnetic field. In order to understand the thermal transport inside the graphene microbridge, we also measure the graphene-based HEB at different bath temperatures between 3 K and 10 K. Detailed experimental results and analysis will be presented.

© (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Abstract-Broadband Terahertz Generation via the Interface Inverse Rashba-Edelstein Effect

C. Zhou, Y. P. Liu, Z. Wang, S. J. Ma, M. W. Jia, R. Q. Wu, L. Zhou, W. Zhang, M. K. Liu, Y. Z. Wu, and J. Qi

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.121.086801

Novel mechanisms for electromagnetic wave emission in the terahertz frequency regime emerging at the nanometer scale have recently attracted intense attention for the purpose of searching next-generation broadband THz emitters. Here, we report broadband THz emission, utilizing the interface inverse Rashba-Edelstein effect. By engineering the symmetry of the $\mathrm{Ag}/\mathrm{Bi}$ Rashba interface, we demonstrate a controllable THz radiation ($\sim 0.1–5\mathrm{THz}$) waveform emitted from metallic $\mathrm{Fe}/\mathrm{Ag}/\mathrm{Bi}$heterostructures following photoexcitation. We further reveal that this type of THz radiation can be selectively superimposed on the emission discovered recently due to the inverse spin Hall effect, yielding a unique film thickness dependent emission pattern. Our results thus offer new opportunities for versatile broadband THz radiation using the interface quantum effects.

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Abstract-Broadband terahertz generation via the interface inverse Rashba-Edelstein effect

C. Zhou, Y. P. Liu, Z. Wang, S. J. Ma, M. W. Jia, R. Q. Wu, L. Zhou, W. Zhang, M. K. Liu, Y. Z. Wu, and J. Qi, 

https://journals.aps.org/prl/accepted/7f07dY95Df118160072f78c38ad2d3d9134dfaf91

Novel mechanisms for electromagnetic wave emission in the terahertz (THz) frequency regime emerging at the nanometer scale have recently attracted intense attention for the purpose of searching next-generation broadband THz emitters. Here, we report broadband THz emission, utilizing the interface inverse Rashba-Edelstein effect. By engineering the symmetry of the Ag/Bi Rashba interface, we demonstrate a controllable THz radiation (\textasciitilde 0.1-5 THz) waveform emitted from metallic Fe/Ag/Bi heterostructures following photo-excitation. We further reveal that this type of THz radiation can be selectively superimposed on the emission discovered recently due to the inverse Spin Hall effect, yielding a unique film thickness dependent emission pattern. Our results thus offer new opportunities for versatile broadband THz radiation using the interface quantum effects. Terahertz (THz) radiation from 0.1--30 THz accesses a diverse group of low-energy elementary excitations in solid-state systems [1], holding great promises for imaging, sensing and security applications [2]. One major challenge in the next generation THz technology is to search novel mechanism(s) providing efficient and broadband THz radiation with a gapless spectrum [3-5]. To date, most broadband THz emission devices [2-5] are based on the femtosecond laser excitations, taking advantage exclusively of the nonlinear or dynamic properties of the electrons. Recently, the emerging ultrafast spintronics [6-13], however, offers an alternative route to the THz emission with the spin-degree of freedom, by converting spin current bursts into THz pulses. In this way, one can effectively generate, control, and detect the spin currents, as well as utilize such spin-to-charge conversion [6-13] within the sub-picosecond timescale to yield efficient ultra-broadband THz emission. Such ultrafast spin-to-charge conversion process in all previous works is mostly based on the inverse Spin Hall effect (ISHE) (14-15), which happens inside the bulk of a metallic system with a strong spin-orbit coupling (SOC). In contrast, the inverse Rashba-Edelstein effect (IREE) occurring at the interfaces with broken inversion symmetry can also provide efficient spin-to-charge conversion [16-19]. In the IREE, the generated charge current in two-dimensional electron gas can be described by [19]$$j_c\propto {\lambda }_{IREE}{j}_s\times \hat{z}$$where ${\lambda }_{IREE}$ is the IREE coefficient which is proportional to the Rashba parameter ${\alpha }_R$, $\hat{z}$ is the direction of the potential gradient (interfacial electric field) perpendicular to the interface, and $j_s$ is the spin current. Although the IREE has been intensively studied under equilibrium or quasi-equilibrium conditions in magnetoresistance measurements [17], non-local spin valves [18], and ferromagnetic resonance experiments [19], it is still elusive whether the IREE can work in femtosecond timescale, and play a vital role in the THz emission. In this work, we report the observation of THz radiation via the interface IREE in the metallic Fe/Ag/Bi heterostructures, which strongly suggests the effect of the interface IREE on the spin-to-charge conversion in femtosecond timescale. This observation brings us to a novel mechanism of emitting ...

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-Broadband terahertz generation via the interface inverse Rashba-Edelstein effect

C. Zhou, Y. P. Liu, Z. Wang, S. J. Ma, M. W. Jia, R.Q. Wu, L. Zhou, W. Zhang, M. K. Liu, Y. Z. Wu, J. Qi

https://128.84.21.199/abs/1804.04765v1

Novel mechanisms for electromagnetic wave emission in the terahertz (THz) frequency regime emerging at the nanometer scale have recently attracted intense attention for the purpose of searching next-generation broadband THz emitters. Here, we report a new mechanism for broadband THz emission, utilizing the interface inverse Rashba-Edelstein effect. By engineering the symmetry of the Ag/Bi Rashba interface, we demonstrate a controllable THz radiation (~0.1-5 THz) waveform emitted from metallic Fe/Ag/Bi heterostructures following photo-excitation. We further reveal that this type of THz radiation can be selectively superimposed on the emission discovered recently due to the inverse Spin Hall effect, yielding a unique film thickness dependent emission pattern. Our results thus offer new opportunities for versatile broadband THz radiation using the interface quantum effects.