Abstract-Modulation of terahertz wave generation from laser-induced filament based on a preionized plasma

Tong Wu, Liquan Dong, Shijing Zhang, Hang Zhao, Kai Kang.Cunlin Zhang, Rui Zhang, Yuejin Zhao, Liangliang Zhang



https://www.sciencedirect.com/science/article/abs/pii/S0030401819302718

We demonstrate the modulation of terahertz wave generation from two-color femtosecond laser filament on the basis of a preionized air plasma background created by a modulation pulse using an orthogonal pumping geometry. This is achieved by adjusting and optimizing the phase difference between the two-color laser fields, which is introduced when the two-color fields goes through the preionized air plasma. In experiments, terahertz time domain waveform is observed using electro-optics sampling setup. Both the energy and the waveform of terahertz wave change significantly with the increase of modulation pulse energy. The results are reasonably coincident with our theoretical simulation based on the plasma photocurrent model. We also experimentally observe the additional relative phase between the two-color laser fields due to the presence of the preionized air plasma. Our results can contribute to the further understanding of the generation mechanism of terahertz wave, enhance the generation efficiency and expand the practical application of terahertz wave.

Abstract-Terahertz Wave Generation From Noble Gas Plasmas Induced by a Wavelength-Tunable Femtosecond Laser

Hang Zhao, Liangliang Zhang, Suxia Huang, Shijing Zhang, Cunlin Zhang

https://ieeexplore.ieee.org/document/8340859

We investigated the effects of pump wavelength on terahertz wave generation via two-color laser-induced plasma in various gas targets including nitrogen and noble gases. The terahertz energy was measured as functions of pump wavelength, input pulse energy, gas species, and pressure. The results suggest that the plasmas in the heavier gases induced by relatively longer wavelength lasers are more likely to generate higher energy terahertz waves. However, the existence of phase slippage in the neutral gases causes distinct fluctuations in the terahertz energy as the gas pressure increases. Meanwhile, the terahertz waves produced in the heavier gas are more likely to saturate at relatively higher pressures or incident optical powers. We propose an ionization rate formula associated with the gas species and pump wavelength to theoretically explain the validity of the experimental results. As a result, the terahertz pulse energy approaches a maximum value of 0.099 μJ per pulse in xenon with a 1500-nm excitation laser, and the terahertz wave to optical pulse energy conversion efficiency reaches 5.6 × 10 -3 , which is an order of magnitude higher than that of a conventional 800-nm pump laser.

Abstract-Excitation-wavelength dependent terahertz wave polarization control in laser-induced filament

Liangliang Zhang, Shijing Zhang, Rui Zhang, Tong Wu, Yuejin Zhao, Cunlin Zhang, and X.-C. Zhang

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-26-32346

We examine the terahertz (THz) emission from air filament driven by two-color lasers with relatively longer wavelengths than 800 nm. The THz energy dependence on the input laser energy increases more rapidly with a longer laser wavelength, and the scaling laws of THz energy as a function of fundamental wavelength vary for different optical powers, which is theoretically validated by considering the optical wavelength-dependent ionization rate. Furthermore, the THz polarization undergoes a continuous rotation as a function of the laser wavelength, since the relative phase and polarization of the two pulses are adjusted through changing the excitation wavelength in the frequency doubling crystal. Our results contribute to the understanding of THz wave generation in a femtosecond laser filament and suggest a practical way to control the polarization of terahertz pulses for potential applications.

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

Abstract-Composite multiscale entropy analysis of reflective terahertz signals for biological tissues

Rui Zhang, Yuezhi He, Kai Liu, Liangliang Zhang, Shijing Zhang, Emma Pickwell-MacPherson, Yuejin Zhao, and Cunlin Zhang

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-20-23669

We demonstrate a composite multiscale entropy (CMSE) method of terahertz (THz) signal complexity analysis to distinguish different biological tissues. The THz signals reflected from fresh porcine skin and muscle tissues were measured and analyzed. The statistically significant difference and separation of the two tissues based on several parameters were analyzed and compared for THz spectroscopy and imaging, which verified the better performance of the CMSE method and further enhancement of the contrast among THz signals that interact with different tissues. This process provides a better analysis and discrimination method for THz spectroscopy and imaging in biomedical applications.

© 2017 Optical Society of America

Abstract-Terahertz wave polyethylene lens based on wave front phase modulation

Tielin Lu; Xiaohu Guo; Lingqin Kong; Yuejin Zhao; Jingshui Zhang; Shijing Zhang

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10383/103830M/Terahertz-wave-polyethylene-lens-based-on-wave-front-phase-modulation/10.1117/12.2273282.short


Terahertz(THz) wave modulator technology, due to its important value of imaging and detecting research. In the paper, we discuss the Polyethylene lens based the terahertz wave front modulation, which is benefit the terahertz wave image technology. Simulation results show that the optical system can extent the depth of imaging field of test objects based on continuous terahertz source. The way to get the image has significant meaning for detection and large image quality.

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