Abstract-Optimization for vertically scanning terahertz attenuated total reflection imaging

Hongxiang Liu, Yuye Wang, Degang Xu, Zhinan Jiang, Jining Li, Limin Wu, Chao Yan, Longhuang Tang, Yixin He, Dexian Yan, Xin Ding, Hua Feng, and Jianquan Yao

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-16-20744

Terahertz attenuated total reflection imaging has been used to develop preliminary applications without any in-depth analysis of the nature of present systems. Based on our proposed vertically scanning imaging system, an analysis of optimum prism design and polarization selection for error reduction is presented theoretically and experimentally, showing good agreement. By taking the secondary reflection inside the prism and the prism deflection into consideration, p-polarized terahertz waves are recommended for prisms with a base angle below 31°, leading to minimum error. This work will contribute to the development of more practical application of terahertz attenuated total reflection scanning imaging in various fields with enhanced performance.

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

Abstract-Terahertz optical properties of nonlinear optical CdSe crystals

Dexian Yan, Degang Xu, Jining Li Yuye Wang, Fei Liang, Jian Wang, Chao Yan, Hongxiang Liu, Jia Shi, Longhuang Tang, Yixin He, Kai Zhong, Zheshuai Lin, Yingwu Zhang,


https://www.sciencedirect.com/science/article/pii/S0925346718301368

We investigate the optical properties of cadmium selenide (CdSe) crystals in a wide terahertz (THz) range from 0.2 to 6 THz by THz time-domain spectroscopy (THz-TDS) and Fourier transform infrared spectroscopy (FTIR). The refractive index, absorption coefficient and transmittance are measured and analyzed. The properties are characterized by several absorption peaks which represent the relevant phonon vibrations modes. The experimental results are in agreement with the theoretical results. The dispersion and absorption properties of CdSe crystal are analyzed in THz range. These properties indicate a good potential for THz sources and THz modulated devices

Abstract-Automatic evaluation of traumatic brain injury based on terahertz imaging with machine learning

Jia Shi, Yuye Wang, Tunan Chen, Degang Xu, Hengli Zhao, Linyu Chen, Chao Yan, Longhuang Tang, Yixin He, Hua Feng, and Jianquan Yao

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-5-6371

The imaging diagnosis and prognostication of different degrees of traumatic brain injury (TBI) is very important for early care and clinical treatment. Especially, the exact recognition of mild TBI is the bottleneck for current label-free imaging technologies in neurosurgery. Here, we report an automatic evaluation method for TBI recognition with terahertz (THz) continuous-wave (CW) transmission imaging based on machine learning (ML). We propose a new feature extraction method for biological THz images combined with the transmittance distribution features in spatial domain and statistical distribution features in normalized gray histogram. Based on the extracted feature database, ML algorithms are performed for the classification of different degrees of TBI by feature selection and parameter optimization. The highest classification accuracy is up to 87.5%. The area under the curve (AUC) scores of the receiver operating characteristics (ROC) curve are all higher than 0.9, which shows this evaluation method has a good generalization ability. Furthermore, the excellent performance of the proposed system in the recognition of mild TBI is analyzed by different methodological parameters and diagnostic criteria. The system can be extensible to various diseases and will be a powerful tool in automatic biomedical diagnostics.

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

Abstract-High-average-power, high-repetition-rate tunable terahertz difference frequency generation with GaSe crystal pumped by 2 μm dual-wavelength intracavity KTP optical parametric oscillator

Dexian Yan, Yuye Wang, Degang Xu, Pengxiang Liu, Chao Yan, Jia Shi, Hongxiang Liu, Yixin He, Longhuang Tang, Jianchen Feng, Jianqin Guo, Wei Shi, Kai Zhong, Yuen H. Tsang, and Jianquan Yao

https://www.osapublishing.org/prj/abstract.cfm?uri=prj-5-2-82&origin=search

We have demonstrated a high-average-power, high-repetition-rate optical terahertz (THz) source based on difference frequency generation (DFG) in the GaSe crystal by using a near-degenerate 2 μm intracavity KTP optical parametric oscillator as the pump source. The power of the 2 μm dual-wavelength laser was up to 12.33 W with continuous tuning ranges of 1988.0–2196.2 nm/2278.4–2065.6 nm for two waves. Different GaSe cystal lengths have been experimentally investigated for the DFG THz source in order to optimize the THz output power, which was in good agreement with the theoretical analysis. Based on an 8 mm long GaSe crystal, the THz wave was continuously tuned from 0.21 to 3 THz. The maximum THz average power of 1.66 μW was obtained at repetition rate of 10 kHz under 1.48 THz. The single pulse energy amounted to 166 pJ and the conversion efficiency from 2 μm laser to THz output was 1.68×10−6$1.68\times {10}^{-6}$. The signal-to-noise ratio of the detected THz voltage was 23 dB. The acceptance angle of DFG in the GaSe crystal was measured to be 0.16°.

© 2017 Chinese Laser Press

Abstract-PAPER High-sensitivity attenuated total internal reflection continuous-wave terahertz imaging

Hongxiang Liu1,2,4, Yuye Wang1,2,3,4, Degang Xu1,2, Limin Wu1,2, Chao Yan1,2, Dexian Yan1,2, Longhuang Tang1,2, Yixin He1,2, Hua Feng3 and Jianquan Yao

http://iopscience.iop.org/article/10.1088/1361-6463/aa7d9a/pdf

We demonstrate an attenuated total internal reflection imaging system. The surface information of the sample on top of a prism can be acquired by two-dimensionally scanning this prism moving in the vertical plane with horizontally incident continuous terahertz waves at a fixed height. The principles and feasibility of this method are investigated. The effective imaging area on the prism, image resolution and polarization dependence of contrast enhancement and stability improvement are analyzed. Examples including solid agar, distilled water and porcine tissue are presented, demonstrating the method's advantages of high sensitivity and simple sample preparation. The experimental and theoretical results consistently show that p-polarization contributes to enhanced image contrast and more stable intensity of the attenuated total internal reflected signal.

Abstract-Energy scaling and extended tunability of terahertz wave parametric oscillator with MgO-doped near-stoichiometric LiNbO3 crystal

Yuye Wang, Longhuang Tang, Degang Xu, Chao Yan, Yixin He, Jia Shi, Dexian Yan, Hongxiang Liu, Meitong Nie, Jiachen Feng, and Jianquan Yao

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-8-8926

A widely tunable, high-energy terahertz wave parametric oscillator based on 1 mol. % MgO-doped near-stoichiometric LiNbO3 crystal has been demonstrated with 1064 nm nanosecond pulsed laser pumping. The tunable range of 1.16 to 4.64 THz was achieved. The maximum THz wave output energy of 17.49 μJ was obtained at 1.88 THz under the pump energy of 165 mJ/pulse, corresponding to the THz wave conversion efficiency of 1.06 × 10−4 and the photon conversion efficiency of 1.59%, respectively. Moreover, under the same experimental conditions, the THz output energy of TPO with MgO:SLN crystal was about 2.75 times larger than that obtained from the MgO:CLN TPO at 1.60 THz. Based on the theoretical analysis, the THz energy enhancement mechanism in the MgO:SLN TPO was clarified to originate from its larger Raman scattering cross section and smaller absorption coefficient.

© 2017 Optical Society of America

Abstract-High-average-power, high-repetition-rate tunable terahertz difference frequency generation with GaSe crystal pumped by 2 μm dual-wavelength intracavity KTP optical parametric oscillator

Dexian Yan, Yuye Wang, Degang Xu, Pengxiang Liu, Chao Yan, Jia Shi, Hongxiang Liu, Yixin He, Longhuang Tang, Jianchen Feng, Jianqin Guo, Wei Shi, Kai Zhong, Yuen H. Tsang, and Jianquan Yao

https://www.osapublishing.org/prj/abstract.cfm?uri=prj-5-2-82

We have demonstrated a high-average-power, high-repetition-rate optical terahertz (THz) source based on difference frequency generation (DFG) in the GaSe crystal by using a near-degenerate 2 μm intracavity KTP optical parametric oscillator as the pump source. The power of the 2 μm dual-wavelength laser was up to 12.33 W with continuous tuning ranges of 1988.0–2196.2 nm/2278.4–2065.6 nm for two waves. Different GaSe cystal lengths have been experimentally investigated for the DFG THz source in order to optimize the THz output power, which was in good agreement with the theoretical analysis. Based on an 8 mm long GaSe crystal, the THz wave was continuously tuned from 0.21 to 3 THz. The maximum THz average power of 1.66 μW was obtained at repetition rate of 10 kHz under 1.48 THz. The single pulse energy amounted to 166 pJ and the conversion efficiency from 2 μm laser to THz output was 1.68×10−6$1.68\times {10}^{-6}$. The signal-to-noise ratio of the detected THz voltage was 23 dB. The acceptance angle of DFG in the GaSe crystal was measured to be 0.16°.

© 2017 Chinese Laser Press

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