Abstract-Switchable multifunctional terahertz metasurfaces employing vanadium dioxide

Xike Li, Shiwei Tang, Fei Ding, Shuomin Zhong, Yuanqing Yang, Tao Jiang,  Jun Zhou, 

https://www.nature.com/articles/s41598-019-41915-6?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+srep%2Frss%2Fcurrent+%28Scientific+Reports%29


In this paper, we design a type of switchable metasurfaces by employing vanadium dioxide (VO2), which possess tunable and diversified functionalities in the terahertz (THz) frequencies. The properly designed homogeneous metasurface can be dynamically tuned from a broadband absorber to a reflecting surface due to the insulator-to-metal transition of VO2. When VO2 is in its insulating state, the metasurface can efficiently absorb the normally incident THz wave in the frequency range of 0.535–1.3 THz with the average absorption of ~97.2%. Once the VO2 is heated up and switched to its fully metallic state, the designed metasurface exhibits broadband and efficient reflection (>80%) in the frequency range from 0.5 to 1.3 THz. Capitalizing on such meta-atom design, we further extend the functionalities by introducing phase-gradients when VO2 is in its fully metallic state and consequently achieve polarization-insensitive beam-steering and polarization-splitting, while maintaining broadband absorption when VO2 is in insulating state.

Abstract-Terahertz oscilloscope for recording time information of ultrashort electron beams

Lingrong Zhao, Zhe Wang, Heng Tang, Rui Wang, Yun Cheng, Chao Lu, Tao Jiang, Pengfei Zhu, Long Hu, Wei Song, Huida Wang, Jiaqi Qiu, Roman Kostin, Chunguang Jing, Sergey Antipov, Peng Wang, Jia Qi, Ya Cheng, Dao Xiang, and Jie Zhang

https://journals.aps.org/prl/accepted/d407dY16M5819b51b9d98708b359b7042e3e658c9

We propose and demonstrate a Terahertz (THz) oscilloscope for recording time information of an ultrashort electron beam. By injecting a laser-driven THz pulse with circular polarization into a dielectric tube, the electron beam is swept helically such that the time information is uniformly encoded into the angular distribution that allows one to characterize both the temporal profile and timing jitter of an electron beam. The dynamic range of the measurement in such a configuration is significantly increased compared to deflection with a linearly polarized THz pulse. With this THz oscilloscope, nearly 50-fold longitudinal compression of a relativistic electron beam to about 15 fs (rms) is directly visualized with its arrival time determined with 3 fs accuracy. This technique bridges the gap between streaking of photoelectrons with optical lasers and deflection of relativistic electron beams with radio-frequency deflectors, and should have wide applications in many ultrashort electron beam based facilities.

Abstract-Fabrication of 4.4 THz quantum cascade laser and its demonstration in high-resolution digital holographic imaging

Tao Jiang, Changle Shen, Zhiqiang Zhan, Ruijiao Zou, Jia Li, Long Fan, Tingting Xiao, Weihua Li, Qing hua Deng, Liping Peng, Xuemin Wang, Weidong Wu,



https://www.sciencedirect.com/science/article/pii/S0925838818331797

In this work, we present our research on the fabrication of high power terahertz quantum cascade laser (THz QCL) with frequency at 4.4 THz and its demonstration in digital holographic imaging. The lasers described in this work are based upon the resonant-phonon active region design and semi-insulating surface-plasmon waveguide. The peak power varies with the size of the ridge and the maximum output power of 95 mW at 10 K in pulsed mode is obtained. The maximum working temperature is 80 K. Interestingly, by changing the injection current, the transverse mode of the laser can be switched between TM00 mode and TM01 mode. With such THz QCL as the light source, the lateral resolution of a home-built digital holographic imaging system can reach 80 μm.

Abstract-Terahertz Streaking of Few-Femtosecond Relativistic Electron Beams

Lingrong Zhao, Zhe Wang, Chao Lu, Rui Wang, Cheng Hu, Peng Wang, Jia Qi, Tao Jiang, Shengguang Liu, Zhuoran Ma, Fengfeng Qi, Pengfei Zhu, Ya Cheng, Zhiwen Shi, Yanchao Shi, Wei Song, Xiaoxin Zhu, Jiaru Shi, Yingxin Wang, Lixin Yan, Liguo Zhu, Dao Xiang, and Jie Zhan

https://journals.aps.org/prx/abstract/10.1103/PhysRevX.8.021061

Streaking of photoelectrons with optical lasers has been widely used for temporal characterization of attosecond extreme ultraviolet pulses. Recently, this technique has been adapted to characterize femtosecond x-ray pulses in free-electron lasers with the streaking imprinted by far-infrared and terahertz (THz) pulses. Here, we report successful implementation of THz streaking for time stamping of an ultrashort relativistic electron beam, whose energy is several orders of magnitude higher than photoelectrons. Such an ability is especially important for MeV ultrafast electron diffraction (UED) applications, where electron beams with a few femtosecond pulse width may be obtained with longitudinal compression, while the arrival time may fluctuate at a much larger timescale. Using this laser-driven THz streaking technique, the arrival time of an ultrashort electron beam with a 6-fs (rms) pulse width has been determined with 1.5-fs (rms) accuracy. Furthermore, we have proposed and demonstrated a noninvasive method for correction of the timing jitter with femtosecond accuracy through measurement of the compressed beam energy, which may allow one to advance UED towards a sub-10-fs frontier, far beyond the approximate 100-fs (rms) jitter.

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Abstract-Terahertz streaking of few-femtosecond relativistic electron beams

Lingrong Zhao, Zhe Wang, Chao Lu, Rui Wang, Cheng Hu, Peng Wang, Jia Qi, Tao Jiang, Shengguang Liu, Zhuoran Ma, Fengfeng Qi, Pengfei Zhu, Ya Cheng, Zhiwen Shi, Yanchao Shi, Wei Song, Xiaoxin Zhu, Jiaru Shi, Yingxin Wang, Lixin Yan, Liguo Zhu, Dao Xiang,  Jie Zhang,

https://journals.aps.org/prx/accepted/d8075K71A261f001129c7ce70c632d2221b6fd030

Streaking of photoelectrons with optical lasers has been widely used for temporal characterization of attosecond extreme ultraviolet pulses. Recently, this technique has been adapted to characterize femtosecond x-ray pulses in free-electron lasers with the streaking imprinted by far-infrared and Terahertz (THz) pulses. Here, we report successful implementation of THz streaking for time-stamping of an ultrashort relativistic electron beam of which the energy is several orders of magnitude higher than photoelectrons. Such ability is especially important for MeV ultrafast electron diffraction (UED) applications where electron beams with a few femtosecond pulse width may be obtained with longitudinal compression while the arrival time may fluctuate at a much larger time scale. Using this laser-driven THz streaking technique, the arrival time of an ultrashort electron beam with 6 fs (rms) pulse width has been determined with 1.5 fs (rms) accuracy. Furthermore, we have proposed and demonstrated a non-invasive method for correction of the timing jitter with femtosecond accuracy through measurement of the compressed beam energy, which may allow one to advance UED towards sub-10 fs frontier far beyond the $\sim$100 fs (rms) jitter.

Abstract- Study of pollution air monitoring system based on space-borne terahertz radiometer

Rui You,  Zheng Lu,  Qinfang Hou,  Tao Jiang,

http://ieeexplore.ieee.org/document/8068480/

A high efficiency, low cost pollution air monitoring system based on space-borne terahertz radiometer is proposed. The radiometers are fixed on the MEO satellites on GPS or BDS. Four operating frequency point of the radiometer are chosen to monitor SO2 and NH3 and the design scheme is shown. The diameter of radiometer Cassegrain reflector antenna is 1,000mm. After reflection, the radiation is splitted into 2 groups by a FSS before entering into the receiver. The simulation results for the antenna and FSS design are both shown. The resolutions of the four operating frequency point are calculated respectively.

Making Terahertz Lasers More Powerful

By Catherine Meyers

Scanning electron microscope image of the terahertz quantum cascade laser.
CREDIT: Wang, et al/AIP Advances

Researchers in China nearly double the continuous output power of a type of terahertz laser, opening up applications in spectroscopy, imaging, remote sensing and more

https://publishing.aip.org/publishing/journal-highlights/making-terahertz-lasers-more-powerful?TRACK=aipp-china

WASHINGTON, D.C., July 26, 2016 -- Researchers have nearly doubled the continuous output power of a type of laser, called a terahertz quantum cascade laser, with potential applications in medical imaging, airport security and more. Increasing the continuous output power of these lasers is an important step toward increasing the range of practical applications. The researchers report their results in the journal AIP Advances, from AIP Publishing.

Terahertz radiation sits between microwaves and infrared light on the electromagnetic spectrum. It is relatively low-energy and can penetrate materials such as clothing, wood, plastic and ceramics. The unique qualitites of terahertz radiation make it an attractive candidiate for imaging, but the ability to produce and control terahertz waves has lagged behind technology for radio, microwave and visible light.

Recently, scientists have made rapid progress on a technology to produce terahertz light called a quantum cascade laser or QCL. Quantum cascade lasers are made from thin layers of material. The thin layers give the laser the valuble property of tunability, meaning the laser can be designed to emit at a chosen wavelength. The output power of terahertz QCLs is also relatively high compared to other terahertz sources, said Xuemin Wang, a researcher in the China Academy of Engineering Physics and first author on the new paper.

Wang and his colleagues' work focuses on even further increasing the output power of terahertz quantum cascade lasers, especially in the mode in which the laser output power is continuous. "In engineering, biomechanics and medical science, the applications require continuous wave mode," Wang said.

By optimizing the material growth and manufacturing process for terahertz QCLs, Wang and his team made a laser with a record output power of up to 230 milliwatts in continuous wave mode. The previous record was 138 milliwatts.

Wang said the new 230 milliwatt laser could be used in air, a challenge for lower-powered lasers since particles in the air can scatter or absorb the laser light before it reaches its target.

The increase demonstrates that the team's method of precisely controlling the growth of the laser's layers can increase output power, Wang said, and he is hopeful that future improvements could bring the continuous power above 1 watt. The 1 watt level has been reached in terahertz QCLs in pulsed wave mode.

Wang said he thinks scientists and engineers could use the new laser as a flexible source of terahertz radiation for spectroscopy, medicial imaging, remote sensing and other applications.

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Article title: 

High-power terahertz quantum cascade lasers with ~0.23 W in continuous wave mode

Authors: 

Xuemin Wang, Changle Shen, Tao Jiang, Zhiqiang Zhan, Qinghua Deng, Weihua Li, Weidong Wu, Ning Yang, Weidong Chu and Suqing Duan

Author affiliations: 

China Academy of Engineering Physics in Sichuan, China and the Institute of Applied Physics and Computational Mathematics in Beijing, China

New metamaterial allows optical transmission gain while retaining negative refraction property

http://www.physorg.com/news/2011-11-metamaterial-transmission-gain-retaining-negative.htmlA new type of active metamaterial that incorporates semiconductor devices into conventional metamaterial structures is demonstrating an ability to have power gain while retaining its negative refraction property, a first in the world of metamaterials research
Our simulation and experimental results show that the addition of the battery powered semiconductor diodes not only provided gain, but also maintained the negative index of this kind of metamaterial," said Dr. Hao Xin of the Department of Electrical and Computer Engineering at the University of Arizona. "It is demonstrated, to our knowledge for the first time, that negative index can be obtained with net gain."
Xin says this type of active metamaterial will be very useful not only in designing and achieving new and high performance microwave circuits and antennas, but can also shed light on metamaterial applications at other spectra including optical frequencies.
Documentation of Xin's research, Manuscript LF12974, titled "Active microwave negative-index metamaterial transmission line with gain," by Tao Jiang, Kihun Chang, Li-Ming Si, et al., has been accepted for publication as a letter in Physical Review Letters, a journal of the American Physical Society. Considered one of the foremost physics letters journals, Physical Review Letters provides rapid publication of short reports of significant fundamental research in all fields of physics.
Metamaterials are engineered composite materials designed to provide unique properties that do not exist naturally in materials, such as negative index of refraction, or the ability to bend and redirect light rather than reflect it. Studies of the engineering and processes of these materials may lead to many new phenomena and exciting applications, including advancing the development of near unlimited or "perfect" lenses and new improved types of microwave antennas and circuits for next level wireless communication and sensing.
Dissipated loss has been a major limitation to these applications becoming reality. Xin notes that the results of this research demonstrate that loss in metamaterial can be compensated, an important step towards practical experimental metamaterial with gain in the microwave domain. These data may also shed light on optical gain systems, Xin said.
Provided by University of Arizona (news : web)