Abstract-Antenna-coupled spintronic terahertz emitters driven by a 1550 nm femtosecond laser oscillator

Applied Physics Letters

 U. Nandi, M. S. Abdelaziz, S. Jaiswal, G. Jakob, O. Gueckstock, S. M. Rouzegar, T. S. Seifert,   M. Kläui, T. Kampfrath,  S. Preu,

Schematic of THz emission from photoexcited FMNM bilayers, plain and microstructured. (a) A femtosecond laser pulse triggers ultrafast spin transport from the FM into the NM layer where the spin current js flowing along the z axis is converted into a charge current jc along the y direction, acting as a source of THz radiation. The direction of the in-plane magnetization of the FM layer is set along the x axis by an external magnetic field Bext. (b) Current distribution in an unstructured (plain) bilayer and (c) the STE bilayer embedded in the gap of an antenna. Note that THz current generation by the ISHE is independent of emitter type and antenna choice.

https://aip.scitation.org/doi/abs/10.1063/1.5089421

We demonstrate antenna-coupled spintronic terahertz (THz) emitters excited by 1550 nm, 90 fs laser pulses. Antennas are employed to optimize THz outcoupling and frequency coverage of ferromagnetic/nonmagnetic metallic spintronic structures. We directly compare the antenna-coupled devices to those without antennas. Using a 200 μm H-dipole antenna and an ErAs:InGaAs photoconductive receiver, we obtain a 2.42-fold larger THz peak-peak signal, a bandwidth of 4.5 THz, and an increase in the peak dynamic range (DNR) from 53 dB to 65 dB. A 25 μm slotline antenna offered 5 dB larger peak DNR and a bandwidth of 5 THz. For all measurements, we use a comparatively low laser power of 45 mW from a commercial fiber-coupled system that is frequently employed in table-top THz time-domain systems.

Abstract-Arrayed free space continuous-wave terahertz photomixers

 

 

S. T. Bauerschmidt, G. H. Döhler, H. Lu, A. C. Gossard, S. Malzer, and S. Preu »View Author Affiliations
http://www.opticsinfobase.org/ol/abstract.cfm?URI=ol-38-18-3673
We present free space coherent arrays of continuous-wave terahertz (THz) photomixers and compare the results to on-chip arrays. By altering the relative phases of the exciting laser signals, the relative THz phase between the array elements can be tuned, allowing for beam steering. In addition, the constructive interference of the emission of  N elements leads to an increase of the focal intensity by a factor of  N² while reducing the beam width by ~ N −¹ below the diffraction limit of a single source. Such array architectures strongly improve the THz power distribution for stand-off spectroscopy and imaging systems while providing a huge bandwidth at the same time. We demonstrate this by beam profiles generated by a  2 x 2 and a  4  x 1 array for a transmission distance of 4.2 m. Spectra between 70 GHz and 1.1 THz have been recorded with these arrays.

Abstract-Inducing an incipient terahertz finite plasmonic crystal in coupled two dimensional plasmonic cavities

 http://prl.aps.org/accepted/d9078Yf3F7815522c9fd50b390b44fda4c68daae4

 G. C. Dyer, G. R. Aizin, S. Preu, N. Q. Vinh, S. J. Allen, J. L. Reno, and E. A. Shaner

Accepted Thursday Aug 23, 2012

We measured a change in the current transport of an antenna-coupled, multi-gate, GaAs/AlGaAs field-effect transistor when terahertz electromagnetic waves irradiated the transistor and attribute the change to bolometric heating of the electrons in the two-dimensional electron channel. The observed terahertz absorption spectrum indicates coherence between plasmons excited under adjacent biased device gates. The experimental results agree quantitatively with a theoretical model we developed that is based on a generalized plasmonic transmission line formalism and describes an evolution of the plasmonic spectrum with increasing electron density modulation from homogeneous to the crystal limit. These results demonstrate an electronically induced and dynamically tunable plasmonic band structure.