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-Design of terahertz-wave Doppler interferometric velocimetry for detonation physics

Applied Physics Letters

Zhao-Hui Zhai, Chang-Lin Sun, Qiao Liu,, Liu-Wei Guo, Yu-Si Liu, Xu Zhang,  De-Tian Wang, Kun Meng, Jiang Li,  Liang-Hui Du,  Shou-Xian Liu, Sen-Cheng Zhong,  Li-Guo Zhu,

(a) Schematic diagram of the TDV system (dashed box) and the detonation testing field. See the supplementary material for the details. (b) THz transmission efficiency vs distance between L3 and L4, assuming the THz beam waist of the TDV output is 15 mm and L4 has a diameter of 50 mm (solid lines) or 30 mm (dashed lines). (c) Simulated THz beam diameter and field depth inside the target for various numerical apertures (NAs) of L4 (assuming n = 1.7). The red circles in (b) and (c) are the parameters of the prototype PDV system.

https://aip.scitation.org/doi/abs/10.1063/1.5142415

The diagnosis of the initiation and growth of detonation in high explosives (HEs) is important in detonation physics. We designed and experimentally demonstrated a non-invasive high-precision free-space terahertz-wave Doppler interferometric velocimetry (TDV) design for diagnosing the transient detonation processes in HEs. The system can non-intrusively record the propagation of the shock/detonation wavefront inside HEs continuously and measure key detonation parameters (position/displacement, detonation velocity, etc.). A detailed quasi-optical design for TDV is discussed. The terahertz penetration ability and the refractive index of representative HEs are presented in the frequency range of 0.2–1.4 THz. Additionally, a typical shock-to-detonation transition of an insensitive high explosive was studied using a prototype 0.212 THz TDV system, which demonstrated the high precision of displacement measurements made using I/Q demodulation. Furthermore, the performance of the TDV technique is discussed. TDV may enable non-invasive and high-precision diagnostics for detonation and shockwave physics.

The National Science Foundation of China (Grant Nos. 61427814, 11704358, and 11604316) and the Foundation of CAEP (Grant No. CX20200001).

The authors own related patents (Nos. CN105807082B, CN105509817B, and CN108398691A).

The authors would like to thank Z. Q. Liu, J. H. Meng, J. H. Tian, P. Gao, and L. H. He for their help with the detonation experiments.

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-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-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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