Abstract-Ghost spintronic THz-emitter-array microscope

Si-Chao Chen, Zheng Feng, Jiang Li, Wei Tan, Liang-Hui Du, Jianwang Cai, Yuncan Ma, Kang He, Haifeng Ding, Zhao-Hui Zhai, Ze-Ren Li, Cheng-Wei Qiu, Xi-Cheng Zhang,  Li-Guo Zhu

https://www.nature.com/articles/s41377-020-0338-4

Terahertz (THz) waves show great potential in nondestructive testing, biodetection and cancer imaging. Despite recent progress in THz wave near-field probes/apertures enabling raster scanning of an object’s surface, an efficient, nonscanning, noninvasive, deep subdiffraction imaging technique remains challenging. Here, we demonstrate THz near-field microscopy using a reconfigurable spintronic THz emitter array (STEA) based on the computational ghost imaging principle. By illuminating an object with the reconfigurable STEA followed by computing the correlation, we can reconstruct an image of the object with deep subdiffraction resolution. By applying an external magnetic field, in-line polarization rotation of the THz wave is realized, making the fused image contrast polarization-free. Time-of-flight (TOF) measurements of coherent THz pulses further enable objects at different distances or depths to be resolved. The demonstrated ghost spintronic THz-emitter-array microscope (GHOSTEAM) is a radically novel imaging tool for THz near-field imaging, opening paradigm-shifting opportunities for nonintrusive label-free bioimaging in a broadband frequency range from 0.1 to 30 THz (namely, 3.3–1000 cm−1).

Abstract-Giant dual-mode graphene-based terahertz modulator enabled by Fabry–Perot assisted multiple reflection

Pei-Ren Tang, Jiang Li, Sen-Cheng Zhong, Zhao-Hui Zhai, Bing Zhu, Liang-Hui Du, Ze-Ren Li, Li-Guo Zhu

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-44-7-1630

We report a high-performance terahertz (THz) modulator with dual operation mode. For the pulse operation mode, the proposed THz modulator has the advantage of high modulation depth (MD) and can operate in a broadband frequency range. We have experimentally achieved a MD larger than 90% for the fifth-order pulse THz echo at 0.8 THz, and the MD stays larger than 75% in a broadband frequency range larger than 1 THz, whereas, for the coherent operation mode, the Fabry–Perot (F-P) interference effect has been taken into consideration and a MD larger than 75% at 0.76 THz has also been realized.

© 2019 Optical Society of America

Abstract-Terahertz wave near-field compressive imaging with a spatial resolution of over λ/100

Si-Chao Chen, Liang-Hui Du, Kun Meng, Jiang Li, Zhao-Hui Zhai, Qi-Wu Shi, Ze-Ren Li, and Li-Guo Zhu

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-44-1-21

We demonstrate terahertz (THz) wave near-field imaging with a spatial resolution of ∼4.5  μm$\sim 4.5\mathrm{\mu m}$using single-pixel compressive sensing enabled by femtosecond-laser (𝑓𝑠$fs$-laser) driven vanadium dioxide (VO2${\mathrm{VO}}_2$)-based spatial light modulator. By 𝑓𝑠$fs$-laser patterning a 180 nm thick VO2${\mathrm{VO}}_2$ nanofilm with a digital micromirror device, we spatially encode the near-field THz evanescent waves. With single-pixel Hadamard detection of the evanescent waves, we reconstructed the THz wave near-field image of an object from a serial of encoded sequential measurements, yielding improved signal-to-noise ratio by one order of magnitude over a raster-scanning technique. Further, we demonstrate that the acquisition time was compressed by a factor of over four with 90% fidelity using a total variation minimization algorithm. The proposed THz wave near-field imaging technique inspires new and challenging applications such as cellular imaging.

© 2018 Optical Society of America

Abstract-Ultrasensitive specific terahertz sensor based on tunable plasmon induced transparency of a graphene micro-ribbon array structure

Pei-ren Tang, Jiang Li, Liang-hui Du, Qiao Liu, Qi-xian Peng, Jian-heng Zhao, Bing Zhu, Ze-ren Li, Li-guo Zhu,

Fig. 1 Conceptual view of the PIT-sensor based on graphene micro-ribbon (GMR). The electromagnetic field is mainly concentrated at the edges of GMR, when excited by a THz wave, leading to the enhanced interaction between THz wave and the analyte. The tunability of the PIT sensor is achieved by changing the bias voltages (V1 and V2) applied on the two sets of GMR arrays.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-23-30655

We proposed an ultrasensitive specific terahertz sensor consisting of two sets of graphene micro-ribbon with different widths. The interference between the plasmon resonances of the wide and narrow graphene micro-ribbons gives rise to the plasmon induced transparency (PIT) effect and enables ultrasensitive sensing in terahertz region. The performances of the PIT sensor have been analyzed in detail considering the thickness and refractive index sensing applications using full wave electromagnetic simulations. Taking advantage of the electrical tunability of graphene’s Fermi level, we demonstrated the specific sensing of benzoic acid with detection limit smaller than 6.35 µg/cm2. The combination of specific identification and enhanced sensitivity of the PIT sensor opens exciting prospects for bio/chemical molecules sensing in the terahertz region.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Label-free monitoring of cell death induced by oxidative stress in living human cells using terahertz ATR spectroscopy

Yi Zou, Qiao Liu, Xia Yang, Hua-Chuan Huang, Jiang Li, Liang-Hui Du, Ze-Ren Li, Jian-Heng Zhao, and Li-Guo Zhu

https://www.osapublishing.org/boe/abstract.cfm?uri=boe-9-1-14&origin=search

We demonstrated that attenuated total reflectance terahertz time-domain spectroscopy (ATR THz-TDS) is able to monitor oxidative stress response of living human cells, which is proven in this work that it is an efficient non-invasive, label-free, real-time and in situ monitoring of cell death. Furthermore, the dielectric constant and dielectric loss of cultured living human breast epithelial cells, and along with their evolution under oxidative stress response induced by high concentration of H2O2, were quantitatively determined in the work. Our observation and results were finally confirmed using standard fluorescence-labeled flow cytometry measurements and visible fluorescence imaging.

© 2017 Optical Society of America under the terms of the OSA Open Access Publishing 

Abstract-Dual-mode tunable terahertz generation in lithium niobate driven by spatially shaped femtosecond laser

Sen-Cheng Zhong, Yu Zhu, Liang-Hui Du, Zhao-Hui Zhai, Jiang Li, Jian-Heng Zhao, Ze-Ren Li, and Li-Guo Zhu

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-15-17066

A new approach for dual-mode (namely broadband mode and narrowband mode) terahertz (THz) pulses generation in a single lithium niobate (LN) crystal excited by spatially shaped tilted-pulse-front femtosecond (fs) laser pulse was proposed and experimentally demonstrated. The two THz emission modes are generated simultaneously while spatially separated. Both central frequency and bandwidth of narrowband THz emission is controllable by in situ tuning the spatial modulation period and beam size of the fs-laser, and the broadband (0.1-1.5 THz) THz emission keeps almost unchanged while tuning the narrowband emission. Further optimization achieves the narrowband THz emission with energy spectral density up to 0.27 μJ/THz and with bandwidth narrowly down to 23 GHz. Such dual-mode THz source is useful for nonlinear THz optics, such as selected resonant THz excitation with broadband THz probe spectroscopy of crystalline matters.

© 2017 Optical Society of America

Abstract-A high-performance broadband terahertz absorber based on sawtooth-shape doped-silicon

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Liang-Hui Du1,2,a), Jiang Li1,2, Zhao-Hui Zhai1,2, Kun Meng1,2, Qiao Liu1,2, Sen-Cheng Zhong1,2, Ping-Wei Zhou1,2, Li-Guo Zhu1,2,b), Ze-Ren Li1,2 and Qi-Xian Peng1,2

a) Electronic mail: Lianghui_Du@163.com

b) Electronic mail: zhuliguo@tsinghua.org.cn

AIP Advances 6, 055112 (2016); http://dx.doi.org/10.1063/1.4950800

http://scitation.aip.org/content/aip/journal/adva/6/5/10.1063/1.4950800?TRACK=RSS

Perfect absorbers with broadband absorption of terahertz (THz) radiation are promising for applications in imaging and detection to enhance the contrast and sensitivity, as well as to provide concealment. Different from previous two-dimensional structures, here we put forward a new type of THz absorber based on sawtooth-shape doped-silicon with near-unit absorption across a broad spectral range. Absorbance over 99% is observed numerically from 1.2 to 3 THz by optimizing the geometric parameters of the sawtooth structure. Our absorbers can operate over a wide range of incident angle and arepolarization insensitive. The underlying mechanisms due to the combination of an air-cavity mode and mode-matching resonance on the air-sawtooth interface are analyzed in terms of the field patterns and electromagnetic power loss features.

Abstract-Optimization of terahertz generation from LiNbO3 under intense laser excitation with the effect of three-photon absorption

Sen-Cheng Zhong, Zhao-Hui Zhai, Jiang Li, Li-Guo Zhu, Jun Li, Kun Meng, Qiao Liu, Liang-Hui Du, Jian-Heng Zhao, and Ze-Ren Li
https://www.osapublishing.org/oe/abstract.cfm?uri=oe-23-24-31313

We proposed a three-dimensional model to simulate terahertz generation from LiNbO3crystal under intense laser excition (up to ~50 mJ/cm2). The impact of three-photon absorption, which leads to free carrier generation and free carrier saturation (when pump fluence above ~10 mJ/cm2) on terahertz generation was investigated. And further with this model, we stated the optimized experimental conditions (incident postion, beam diameter, and pulse duration, etc) for maximum generation efficiency in commonly-used tilted-pulse-front scheme. Red shift of spectrum, spatial distribution “splitting” effects of emitted THz beam, and primilary experimental verification under intense laser excitation are given.

© 2015 Optical Society of America

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Abstract-Polarization dependent terahertz generation efficiency by optical rectification in LiNbO3

Kun Meng, Sen-Cheng Zhong, Li-Guo Zhu, Qiao Liu, Ze-Ren Li

China Academy of Engineering Physics (China)

http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=2089967

Proc. SPIE 9444, International Seminar on Photonics, Optics, and Its Applications (ISPhOA 2014), 94440J (January 9, 2015); doi:10.1117/12.2075161

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Optical rectification of laser pulses in LiNbO3 by tilted-pulse-front pumping (TPFP) is a powerful way to generate terahertz(THz) pulses. However, comprehensive theoretical analysis is still lack. In this work, we first established and presented a detailed theoretical model for TPFP scheme, which then was used to analyze the pump beam polarization dependent terahertz pulses generated by this scheme. The results indicate that one can change the polarization state of the terahertz pulse by changing the pump beam polarization. A scheme using tilted-pulse-front pumping was also set up, and the generated terahertz pulses have maximal conversion efficiency when the pump beam electric field vector is parallel to the crystal axis, which is consistent with theoretical model. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Abstract-Terahertz pulsed spectroscopy of paraffin-embedded brain glioma

Kun Meng ; Tu-nan Chen ; Tao Chen ; Li-guo Zhu ; Qiao Liu ; Zhao Li ; Fei Li; Sen-cheng Zhong ; Ze-ren Li ; Hua Feng ; Jian-heng Zhao

[-] Author Affiliationshttp://biomedicaloptics.spiedigitallibrary.org/article.aspx?articleid=1887716

Kun Meng

China Academy of Engineering Physics, Institute of Fluid Physics, Interdisciplinary Laboratory of Physics and Biomedicine, No. 64, Mianshan Road, Mianyang, Sichuan 621900, China

China Academy of Engineering Physics, Terahertz Research Center, Mianyang, Sichuan 621900, China

Tu-nan Chen

China Academy of Engineering Physics, Institute of Fluid Physics, Interdisciplinary Laboratory of Physics and Biomedicine, No. 64, Mianshan Road, Mianyang, Sichuan 621900, China

Third Military Medical University, Southwest Hospital, Department of Neurosurgery, No. 30, Gaotanyan Street, Shapingba, Chongqing 400038, China

Tao Chen, Jian-heng Zhao

China Academy of Engineering Physics, Institute of Fluid Physics, Interdisciplinary Laboratory of Physics and Biomedicine, No. 64, Mianshan Road, Mianyang, Sichuan 621900, China

Li-guo Zhu, Qiao Liu, Sen-cheng Zhong, Ze-ren Li

China Academy of Engineering Physics, Institute of Fluid Physics, Interdisciplinary Laboratory of Physics and Biomedicine, No. 64, Mianshan Road, Mianyang, Sichuan 621900, China

China Academy of Engineering Physics, Terahertz Research Center, Mianyang, Sichuan 621900, China

Zhao Li, Fei Li, Hua Feng

Third Military Medical University, Southwest Hospital, Department of Neurosurgery, No. 30, Gaotanyan Street, Shapingba, Chongqing 400038, China

J. Biomed. Opt. 19(7), 077001 (Jul 07, 2014). doi:10.1117/1.JBO.19.7.077001

History: Received April 11, 2014; Revised June 4, 2014; Accepted June 13, 2014

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 Open Access

Abstract.  The refractive indices, absorption coefficients, and complex dielectric constants of paraffin-embedded brain glioma and normal brain tissues have been measured by a terahertz time-domain spectroscopy (THz-TDS) system in the 0.2- to 2.0-THz range. The spectral differences between gliomas and normal brain tissues were obtained. Compared with normal brain tissue, our results indicate that paraffin-embedded brain gliomas have a higher refractive index, absorption coefficient, and dielectric constant. Based on these results, the best THz frequencies for different methods of paraffin-embedded brain glioma imaging, such as intensity imaging, coherent imaging with continuum THz sources, and THz pulsed imaging with short-pulsed THz sources, are analyzed.

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