Abstract-Generation of a terahertz collimated top-hat beam by using two thin diffractive phase plates

Xi Ye, Feidi Xiang, Chengwu You, Kejia Wang, Zhengang Yang, Jinsong Liu, and Shenglie Wang

Fig. 1 Configuration of THz top-hat beam shaping system with two optical elements, (a). 3D-printed refractive aspheric lenses, (b). 3D-printed diffractive phase plates.

https://www.osapublishing.org/osac/abstract.cfm?uri=osac-1-4-1341

We propose an efficient approach for shaping a terahertz (THz) Gaussian beam to a collimated top-hat beam by using two thin diffractive phase plates. The phase plates are designed based on the phase retrieve algorithm and fabricated by well-developed 3D-printing technology. The designed THz top-hat beam is experimentally realized at 0.3-THz. Both the calculated root mean square (RMS) uniformity and fraction of the total beam power of the output top-hat beam are over 80%, respectively. Additionally, the comparison between our approach and the traditional system containing of two refractive aspheric lenses is performed, showing that our beam shaping system has higher energy utilization.

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

Abstract-A proposed approach for detecting terahertz pulses by using double few-cycle laser pulses with opposite carrier envelope phases

Kejia Wang, Xinyang Gu, Zhenwei Zhang, Zhengang Yang, Jinsong Liu, and Shenglie Wang

https://www.osapublishing.org/col/abstract.cfm?uri=col-16-9-090401&origin=search

Previous research shows that few-cycle laser (FCL) pulses with low energy and without a bias field can be used to coherently detect terahertz (THz) pulses. As we know, it is very difficult to stabilize the carrier envelope phase (CEP) of FCL pulses, i.e., there are some random fluctuations for the CEP. Here we theoretically investigate the influence of such instability on the accuracy of THz detection. Our results show that although there is an optimum CEP for THz detection, the fluctuations of the CEP will lead to terrible thorns on the detected THz waveform. In order to solve this problem, we propose an approach using two few-cycle laser pulses with opposite CEPs, i.e., their CEPs are differed by π.

© 2018 Chinese Laser Press

Abstract-High-precision terahertz frequency modulated continuous wave imaging method using continuous wavelet transform

Yu Zhou, Tianyi Wang,  Bing Dai,  Wenjun Li,  Wei Wang,  Chengwu You, Kejia Wang, Jinsong Liu; Shenglie Wang,  Zhengang Yang

https://www.spiedigitallibrary.org/journals/Optical-Engineering/volume-57/issue-2/023108/High-precision-terahertz-frequency-modulated-continuous-wave-imaging-method-using/10.1117/1.OE.57.2.023108.short?SSO=1

Inspired by the extensive application of terahertz (THz) imaging technologies in the field of aerospace, we exploit a THz frequency modulated continuous-wave imaging method with continuous wavelet transform (CWT) algorithm to detect a multilayer heat shield made of special materials. This method uses the frequency modulation continuous-wave system to catch the reflected THz signal and then process the image data by the CWT with different basis functions. By calculating the sizes of the defects area in the final images and then comparing the results with real samples, a practical high-precision THz imaging method is demonstrated. Our method can be an effective tool for the THz nondestructive testing of composites, drugs, and some cultural heritages.

© 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)

Abstract-Terahertz circular Airy vortex beams

Changming Liu, Jinsong Liu, Liting Niu, Xuli Wei, Kejia Wang,  Zhengang Yang

https://www.nature.com/articles/s41598-017-04373-6

Vortex beams have received considerable research interests both in optical and millimeter-wave domain since its potential to be utilized in the wireless communications and novel imaging systems. Many well-known optical beams have been demonstrated to carry orbital angular momentum (OAM), such as Laguerre-Gaussian beams and high-order Bessel beams. Recently, the radially symmetric Airy beams that exhibit an abruptly autofocusing feature are also demonstrated to be capable of carrying OAM in the optical domain. However, due to the lack of efficient devices to manipulate terahertz (THz) beams, it could be a challenge to demonstrate the radially symmetric Airy beams in the THz domain. Here we demonstrate the THz circular Airy vortex beams (CAVBs) with a 0.3-THz continuous wave through 3D printing technology. Assisted by the rapidly 3D-printed phase plates, individual OAM states with topological charge l ranging from l = 0 to l = 3 and a multiplexed OAM state are successfully imposed into the radially symmetric Airy beams. We both numerically and experimentally investigate the propagation dynamics of the generated THz CAVBs, and the simulations agree well with the observations.

Abstract-Discrimination of orbital angular momentum modes of the terahertz vortex beam using a diffractive mode transformer

Discrimination of orbital angular momentum modes of the terahertz vortex beam using a diffractive mode transformer

Changming Liu, Xuli Wei, Liting Niu, Kejia Wang, Zhengang Yang, and Jinsong Liu

We present an efficient method to discriminate orbital angular momentum (OAM) of the terahertz (THz) vortex beam using a diffractive mode transformer. The mode transformer performs a log-polar coordinate transformation of the input THz vortex beam, which consists of two 3D-printed diffractive elements. A following lens separates each transformed OAM mode to a different lateral position in its focal plane. This method enables a simultaneous measurement over multiple OAM modes of the THz vortex beam. We experimentally demonstrate the measurement of seven individual OAM modes and two multiplexed OAM modes, which is in good agreement with simulations.

© 2016 Optical Society of America

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Abstract-Oscillation effect in frequency domain current from a photoconductive antenna via double-probe-pulse terahertz detection technique

Qi Jin, 

Jinsong Liu, 

Kejia Wang, 

Zhengang Yang, 

Shenglie Wang, 

Kefei Ye

http://link.springer.com/article/10.1007/s12200-015-0491-1

Via constructing a special terahertz time domain spectroscopy (THz-TDS) system in which two femtosecond (fs) laser pulses were used as probe pulses to excite a photoconductive (PC) THz detector, the time behavior of the current from the detector was measured. The corresponding theoretical analysis was performed by a well-known equivalent-circuit model. When the time domain current was transformed to frequency domain, an oscillation effect was observed. The oscillation frequency was decided by the time delay between the two probe pulses. The number of the extrema in the frequency domain current curve was proportion to the pulse interval in 0.1–2 THz. A method to measure the interval of fs laser pulses was proposed. It is important for applications of fs laser pulses or train.