Abstract-Distinctive Performance of Terahertz Photodetection Driven by Charge‐Density‐Wave Order in CVD‐Grown Tantalum Diselenide

Lin Wang,  Jin Wang,  Changlong Liu,   Huang Xu,  Ang Li,  Dacheng Wei,   Yunqi Liu,  Gang Chen,  Xiaoshuang Chen,  Wei Lu,

https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.201905057?af=R

The quantum behavior of carriers in solid is the foundation of modern electronic and optoelectronic technology, but it is still facing huge challenges within inherited single‐particle quantum processes working at the millimeter wave/terahertz (THz) band. Here, a straightforward strategy for the direct detection of millimeter wave/THz photons in a sub‐wavelength metal‐TaSe2‐metal structure under strong interaction with a localized field of surface plasmon is proposed. By breaking the inversion symmetry under the perturbations of electric field and atomic reconstruction from van der Waals integration, the nonequilibrium electronic states under a radiant field can be manipulated in a collective fashion, leading to a large photocurrent responsivity over 40 A W−1 and noise equivalent power less than 1 pW Hz−1/2 even at room temperature. A more than 40‐fold enhancement in responsivity is achieved when transitioning from the normal phase to the CDW phase. The findings shed fresh light on the understanding of the delicate balance in the charge‐ordered phase, and facilitate the exploitation of a correlated electron system for optoelectronic applications in fields of security, remote sensing, and imaging.

Abstract-High power THz coherent Cherenkov radiation based on a separated dielectric loaded waveguide

Shimin Jiang, Weiwei Li, Zhigang He, Ruixuan Huang, Qika Jia, Lin Wang, Yalin Lu,



https://www.sciencedirect.com/science/article/pii/S0168900219301202

In this paper, we propose a new type of dielectric loaded waveguide structure named separated dielectric loaded waveguide (SDLW), whose dielectric layer and metal layer are separated with each other. The characters of wakefield inside SDLW are studied in details by theory analysis and numerical simulation. Compared with the ordinary dielectric loaded waveguide, the peak power of Terahertz coherent Cherenkov radiation (CCR) excited by the short relativistic electron bunch can be enhanced by over one order. Therefore, this new structure offers a promising candidate for high power THz source

Abstract-Design of a Pre-Bunched THz Free Electron Laser

Ruixuan Huang, Weiwei Li,  Zhouyu Zhao, Heting Li, Jigang Wang, Tian Ma, Qiuping Huang, Zhigang He, Qika Jia, Lin Wang, Yalin Lu

https://www.mdpi.com/2571-712X/1/1/21/htm

Terahertz (THz) radiation has attracted much attention in new scientific and industrial applications. There has been significant recent progress in generating THz with accelerators. To investigate the collective behavior of electron dynamics, we have proposed a new high throughput material characterization system, which supplies a multiple light source. The system includes a pre-bunched THz free electron laser (FEL), which is a high-power narrow-band THz source with a wide tuning range of frequency. The physical design with the main components of the facility is introduced, and the simulation results are illustrated. Radiation of 0.5–3.0 THz is obtained by the fundamental wave of the pre-bunched beam, and radiation covering 3.0–5.0 THz is realized by second harmonic generation. As the simulation shows, intense THz radiation could be achieved in a frequency from 0.5–5.0 THz, with a peak power of several megawatts (MWs) and a bandwidth of a few percent.

Abstract-Multicolor Terahertz Frequency Mixer Using Multibunching of Free-Electron Beams

Weihao Liu, Linbo Liang, Qika Jia, Lin Wang, and Yalin Lu

https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.10.034031

We propose a free-electron-beam (FEB)-driven frequency mixer for generating terahertz-wave radiation. It employs an initial steady-current FEB to drive two cascaded gratings. On the first grating, the FEB is macrobunched by interacting with the self-stimulated backward slow waves. On the second grating, which operates at high harmonics of the first grating, it is further microbunched at high frequencies, producing mixed bunching components within the FEB. The multibunched FEB then generates a series of superradiant Smith-Purcell radiations from the second grating, achieving multicolor radiations in the terahertz region. The radiation can be tuned by adjusting the beam energy, covering the frequency range from 0.8 to 1.8 THz. It is a promising broad-tunable and multicolor terahertz source.

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Abstract-Ultrasensitive Room‐Temperature Terahertz Direct Detection Based on a Bismuth Selenide Topological Insulator

Weiwei Tang,   Antonio Politano,  Cheng Guo,   Wanlong,  Guo,   Changlong Liu,   Lin Wang,  Xiaoshuang Chen,  Wei Lu,

https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.201801786

Despite their huge application capabilities, millimeter‐ and terahertz‐wave photodetectors still face challenges in the detection scheme. Topological insulators (TIs) are predicted to be promising candidates for long‐wavelength photodetection, due to the presence of Dirac fermions in their topologically protected surface states. However, photodetection based on TIs is usually hindered by the large dark current, originating from the mixing of bulk states with topological surface states (TSSs) in most realistic samples of TIs. Here millimeter and terahertz detectors based on a subwavelength metal–TI–metal (MTM) heterostructure are demonstrated. The achieved photoresponse stems from the asymmetric scattering of TSS, driven by the localized surface plasmon‐induced terahertz field, which ultimately produces direct photocarriers beyond the interband limit. The device enables high responsivity in both the self‐powered and bias modes even at room temperature. The achieved responsivity is over 75 A/W, with response time shorter than 60 ms in the self‐powered mode. Remarkably, the responsivity increases by several orders of magnitude in the biased configuration, with the noise‐equivalent power (NEP) of 3.6 × 10−13 W Hz−1/2 and a detectivity of 2.17 × 1011cm Hz−1/2 W−1 at room temperature. The detection performances open a way toward realistic exploitation of TIs for large‐area, real‐time imaging within long‐wavelength optoelectronics.

Abstract-Towards sensitive terahertz detection via thermoelectric manipulation using graphene transistors

Changlong Liu, Lei Du, Weiwei Tang, Dacheng Wei, Jinhua Li, Lin Wang, Gang Chen, Xiaoshuang Chen,  Wei Lu

https://www.nature.com/articles/s41427-018-0032-7

Graphene has been highly sought after as a potential candidate for hot-electron terahertz (THz) detection benefiting from its strong photon absorption, fast carrier relaxation, and weak electron-phonon coupling. Nevertheless, to date, graphene-based thermoelectric THz photodetection is hindered by low responsivity owing to relatively low photoelectric efficiency. In this work, we provide a straightforward strategy for enhanced THz detection based on antenna-coupled CVD graphene transistors with the introduction of symmetric paired fingers. This design enables switchable photodetection modes by controlling the interaction between the THz field and free hot carriers in the graphene-channel through different contacting configurations. Hence a novel “bias-field effect” can be activated, which leads to a drastic enhancement in THz detection ability with maximum responsivity of up to 280 V/W at 0.12 THz relative to the antenna area and a Johnson-noise limited minimum noise-equivalent power (NEP) of 100 pW/Hz0.5at room temperature. The mechanism responsible for the enhancement in the photoelectric gain is attributed to thermophotovoltaic instead of plasma self-mixing effects. Our results offer a promising alternative route toward scalable, wafer-level production of high-performance graphene detectors.

Abstract-Graphene-based broadband terahertz detector integrated with a square-spiral antenna

Wanlong Guo, Lin Wang, Xiaoshuang Chen, Changlong Liu, Weiwei Tang, Cheng Guo, Jin Wang, and Wei Lu

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-43-8-1647

Raising interest in terahertz radiation (loosely defined as the 0.1∼10  THz$0.1\sim 10\mathrm{THz}$ frequency range) for the application-oriented issues in everyday life requires progressive development of fast, sensitive, and portable photodetectors. In this Letter, a broadband graphene-based terahertz detector with good integrability and sensitivity at room temperature is proposed. It is based on the chemical vapor deposited-grown graphene integrated with a square-spiral metal antenna which, on one hand, improves the efficiency for electromagnetic coupling and, on the other hand, facilitates the hot-electron photo-thermoelectric process for photodetection. Sensitivity over 28 V/W at room temperature and noise-equivalent power of less than 0.35  nW/Hz0.5$0.35\mathrm{nW}/{\mathrm{Hz}}^{0.5}$ are demonstrated in reference to the incident power. The presented results appealingly open an alternative way to realize chip-level graphene-based terahertz optoelectronics with good scalability and expected performance for targeted terahertz applications.

© 2018 Optical Society of America

Abstract-Wavelength-swept fiber laser based on bidirectional used linear chirped fiber Bragg grating

Lin Wang, Minggui Wan, Zhenkun Shen, Xudong Wang, Yuan Cao, Xinhuan Feng, and Bai-ou Guan

https://www.osapublishing.org/prj/abstract.cfm?uri=prj-5-3-219&origin=search

A wavelength-swept fiber laser is proposed and successfully demonstrated based on a bidirectional used linear chirped fiber Bragg grating (LC-FBG). The wavelength-swept operation principle is based on intracavity pulse stretching and compression. The LC-FBG can introduce equivalent positive and negative dispersion simultaneously, which enables a perfect dispersion matching to obtain wide-bandwidth mode-locking. Experimental results demonstrate a wavelength-swept fiber laser that exhibits a sweep rate of about 5.4 MHz over a 2.1 nm range at a center wavelength of 1550 nm. It has the advantages of simple configuration and perfect dispersion matching in the laser cavity.

© 2017 Chinese Laser Press

Abstract-Surface plasmons in a nanostructured black phosphorus flake

Xinyue Ni, Lin Wang, Jinxuan Zhu, Xiaoshuang Chen, and Wei Lu

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-42-13-2659&origin=search

Recent rediscovered layered material-black phosphorous with a puckered honeycomb atomic structure has experienced an upsurge in demand owing to its exotic physical properties such as layer-independent direct bandgap and linear dichroism. This Letter presents plasmonic properties of the nanostructured BP flake and its unprecedented capability of wide-band photon manipulation within the deep subwavelength scale. Owing to its anisotropic characteristic in band structure and moderate mobility, a strong layer number and polarization dependences of the plasmon resonance with frequencies ranging from infrared (IR) to terahertz have been found. Oblique plasmons have been observed in the square array of a black phosphorus (BP) flake, with the resonant frequency tuned in-situ, either electrically or optically, plus strong plasmon-induced absorption. Such advantages place BP as the best alternate candidate of plasmonic materials for ultra-scaled optoelectronic integration from terahertz to mid-IR.

© 2017 Optical Society of America

Abstract-High-harmonic terahertz Smith-Purcell free-electron-laser with two tandem cylindrical-gratings

Linbo Liang, Weihao Liu, Qika Jia, Lin Wang, and Yalin Lu

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-3-2960

A modified Smith-Purcell free-electron-laser based on two tandem cylindrical-gratings is proposed. The preset grating with larger size, operating in the slow-wave condition, is to prebunch the initial continuous electron-beam, and the postpositive grating with smaller size, operating in the fast-wave condition, is used as the main radiator. Compared with traditional Smith-Purcell free-electron-lasers operating at the second harmonic of the bunched-beam, the present scheme operates at much higher harmonics, fifth and sixth harmonics have been achieved, and the radiation frequency is greatly increased consequently. And also the radiation power is enhanced by tens of times. Thus it could be developed as an efficient terahertz source with frequency being over 0.5 THz in practice.

© 2017 Optical Society of America

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Abstract-Toward Sensitive Room-Temperature Broadband Detection from Infrared to Terahertz with Antenna-Integrated Black Phosphorus Photoconductor

http://onlinelibrary.wiley.com/doi/10.1002/adfm.201604414/abstract;jsessionid=6D6EEA515BD415551858CA0C703C0EFC.f01t01?systemMessage=Wiley+Online+Library+Journal+subscribe+and+renew+pages+for+some+journals+will+be+unavailable+on+Wednesday+11th+January+2017+from+06%3A00-12%3A00+GMT+%2F+01%3A00-07%3A00+EST+%2F+14%3A00-20%3A00+SGT+for+essential+maintenance.+Apologies+for+the+inconvenience

Graphene-like two-dimensional materials (graphene, transition-metal dichalcogenides (TMDCs)) have received extraordinary attention owing to their rich physics and potential applications in building nanoelectronic and nanophotonic devices. Recent works have concentrated on increasing the responsivity and extending the operation range to longer wavelengths. However, the weak absorption of gapless graphene, and the large bandgap (>1 eV) and low mobility in TMDCs have limited their spectral usage to only a narrow range in the visible spectrum. In this work, we demonstrate for the first time a high-performance, antenna-integrated, black phosphorus (BP)-based photoconductor with ultra-broadband detection from the infrared to terahertz frequencies. The good trade-off between the moderate bandgap and good mobility results in a broad spectral absorption that is superior to that of graphene. Different photoconductive mechanisms, such as photothermoelectric (PTE), bolometric, and electron–hole generation can be distinguished depending on the device geometry, incident wavelength, and power. Especially, the photoconductive response remains highly efficient, even when the photon energy is extended to the terahertz (THz) band at room temperature, which is driven by the thermoelectric-induced well. The proposed photodetectors have a superior performance with an excellent sensitivity of over 300 V W−1, low noise equivalent power (NEP) (smaller than 1 nW Hz−0.5(10 pW Hz−0.5) with respect to the incident (absorbed) power), and fast response, all of which play key roles in multispectral biological imaging, remote sensing, and optical communications.