Abstract-Manipulation of polarizations for broadband terahertz waves emitted from laser plasma filaments

Zhelin Zhang, Yanping Chen, Sen Cui, Feng He, Min Chen, Zhen Zhang, Jin Yu, Liming Chen, Zhengming Sheng, Jie Zhang,

https://www.nature.com/articles/s41566-018-0238-9?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+nphoton%2Frss%2Fcurrent+%28Nature+Photonics+-+Issue%29

Polarization control of broadband terahertz waves is essential for applications in many areas, such as materials science, medical and biological diagnostics, near-field communications and public securities. Conventional methods for polarization control are limited to narrow bandwidth and often with low efficiency. Here, based on theoretical and experimental studies, we demonstrate that the two-colour laser scheme in gas plasma can provide effective control of elliptically polarized terahertz waves, including their ellipticity, azimuthal angle and chirality. This is achieved with a circularly polarized laser at the fundamental frequency and its linearly polarized second harmonic, a controlled phase difference between these two laser components, as well as a suitable length of the laser plasma filament. Flexible control of ellipticity and azimuthal angle is demonstrated with our theoretical model and systematic experiments. This offers a unique and flexible technique on the polarization control of broadband terahertz radiation suitable for a wide range of applications.

Abstract-A High-Power Broadband Terahertz Source Enabled by Three-Dimensional Light Confinement in a Plasmonic Nanocavity

Nezih Tolga Yardimci, Semih Cakmakyapan, Soroosh Hemmati,  Mona Jarrahi,

https://www.nature.com/articles/s41598-017-04553-4

The scope and potential uses of time-domain terahertz imaging and spectroscopy are mainly limited by the low optical-to-terahertz conversion efficiency of photoconductive terahertz sources. State-of-the-art photoconductive sources utilize short-carrier-lifetime semiconductors to recombine carriers that cannot contribute to efficient terahertz generation and cause additional thermal dissipation. Here, we present a novel photoconductive terahertz source that offers a significantly higher efficiency compared with terahertz sources fabricated on short-carrier-lifetime substrates. The key innovative feature of this source is the tight three-dimensional confinement of the optical pump beam around the terahertz nanoantennas that are used as radiating elements. This is achieved by means of a nanocavity formed by plasmonic structures and a distributed Bragg reflector. Consequently, almost all of the photo-generated carriers can be routed to the terahertz nanoantennas within a sub-picosecond time-scale. This results in a very strong, ultrafast current that drives the nanoantennas to produce broadband terahertz radiation. We experimentally demonstrate that this terahertz source can generate 4 mW pulsed terahertz radiation under an optical pump power of 720 mW over the 0.1–4 THz frequency range. This is the highest reported power level for terahertz radiation from a photoconductive terahertz source, representing more than an order of magnitude of enhancement in the optical-to-terahertz conversion efficiency compared with state-of-the-art photoconductive terahertz sources fabricated on short-carrier-lifetime substrates.

Abstract-Fast design of broadband terahertz diffusion metasurfaces

Jie Zhao, Qiang Cheng, Tian Qi Wang, Wei Yuan, and Tie Jun Cui

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-2-1050

A method for fast design of broadband terahertz diffusion metasurface is presented. The proposed metasurface is composed by three kinds of simply patterned elements with different resonant properties. To obtain the best broadband performance with the lowest backward reflections, a genetic algorithm is developed to manipulate the resonances for the fast determination of element geometries. An inverse discrete Fourier transform method is used to predict the scattering pattern of the metasurface with high accuracy and low time consumption, significantly enhancing the efficiency of the array-pattern design. The proposed fast design flow will benefit a broad range of terahertz applications, such as biological detection and imaging.

© 2017 Optical Society of America

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Abstract-Freely Tunable Broadband Polarization Rotator for Terahertz Waves

Fan, R.-H., Zhou, Y., Ren, X.-P., Peng, R.-W., Jiang, S.-C., Xu, D.-H., Xiong, X., Huang, X.-R. and Wang, M. (2014), Freely Tunable Broadband Polarization Rotator for Terahertz Waves. Adv. Mater.. doi: 10.1002/adma.201404981

Author Information

1. 1
   National Laboratory of Solid State Microstructures and School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing, China
2. 2
   Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois, USA

^*E-mail: rwpeng@nju.edu.cn, xiahuang@aps.anl.gov, muwang@nju.edu.cn

Publication History

1. Article first published online: 28 DEC 2014
2. Manuscript Revised: 21 NOV 2014
3. Manuscript Received: 31 OCT 2014

http://onlinelibrary.wiley.com/doi/10.1002/adma.201404981/abstract

For the first time a freely tunable polarization rotator for broadband terahertz waves is demonstrated using a three-rotating-layer metallic grating structure, which can conveniently rotate the polarization of a linearly polarized terahertz wave to any desired direction with nearly perfect conversion efficiency. This low-cost, high-efficiency, and freely tunable device has potential applications as material analysis, wireless communication, and THz imaging.

Abstract-Focus free terahertz reflection imaging and tomography with Bessel beams

S. F. Busch, 

G. E. Town, 

M. Scheller, 

M. Koch

http://link.springer.com/article/10.1007/s10762-014-0129-1


A broadband terahertz (THz) reflection imaging system with high spatial resolution over a large depth of field is reported. A THz axicon lens producing a truncated THz Bessel beam with a linear focus exceeding 120 mm in length, and with the diameter of the central lobe less than 2 mm was used for imaging in a reflection geometry employing a pulsed THz time-domain spectrometer. With numerical post-processing, it was possible to reconstruct the three dimensional shape of the scanned object