Abstract-Multi-layered full-field phase imaging using continuous-wave terahertz ptychography

Dayong Wang, Bing Li, Lu Rong, Fangrui Tan, John J. Healy, Jie Zhao, and Yunxin Wang

https://www.blogger.com/blogger.g?blogID=124073320791841682#editor/target=post;postID=6482707098183844787

Due to the unique properties of terahertz (THz) waves, THz phase imaging has been widely investigated to retrieve the absorption and phase modulation of dielectric two-dimensional thin samples, as well as multiple stacked samples. In this Letter, we apply the three-dimensional ptychographic iterative engine algorithm for continuous-wave THz full-field multi-layered phase imaging. The complex-valued transmission function of two-layered polypropylene thin plates and the corresponding probe function are reconstructed, respectively, which are immune to crosstalk of different layers. The phenomenon of the field-of-view enlargement at the second object layer is observed. This lensless compact imaging method can be potentially used for THz three-dimensional imaging.

© 2020 Optical Society of America

Abstract-Continuous-wave Terahertz Computed Tomography for Analysing Biological Bone

Bin Li, Dayong Wang, Lu Rong, Jie Zhao, Yunxin Wang, and Xiaoyu Shi

https://www.osapublishing.org/abstract.cfm?URI=dh-2019-Th4B.5

We reported an application of terahertz computed tomography for bone density analysis. Two-dimensional cross-sectional images of the chicken ulna were obtained through the continuous-wave terahertz imaging system.

© 2019 The Author(s)

Abstract-Probe position correction based on overlapped object wavefront cross-correlation for continuous-wave terahertz ptychography

Lu Rong, Chao Tang, Dayong Wang, Bing Li, Fangrui Tan, Yunxin Wang, and Xiaoyu Shi

Fig. 1 A schematic representation of the proposed algorithm. If the initial probe position is determined, the following probe positions are successively estimated by Eqs. (2) – (5).

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-2-938

Continuous-wave terahertz ptychography is a promising large field-of-view lensless terahertz phase imaging method. Inaccurate probe positions would severely degrade the reconstruction quality, as compared to other spectral bands. In this paper, we propose a probe position correction method based on cross-correlation registration on overlapped regions of the object wavefront for terahertz ptychography. The translation errors could be minimized in the order of 0.01 pixels. The simulation results suggest good computational efficiency, correction, and reconstruction accuracy. We perform continuous-wave terahertz ptychography on a cicada’s forewing. The subcosta and the first radius vein are distinguished after position correction. The probe position distribution reveals that the tilt angle between the object plane and the recording plane is 0.26°.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Numerical and experimental analysis of Bessel beam properties based on continuous-wave terahertz radiation

Zhihao Xu, Lu Rong, Dayong Wang, Bin Li, Yanlin Zhao, Jie Zhao, Yunxin Wang

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10826/108261C/Numerical-and-experimental-analysis-of-Bessel-beam-properties-based-on/10.1117/12.2501241.short

Terahertz imaging technology has been widely used in various fields. In continuous-wave terahertz imaging system, when the large size object is located at the unfocused position, Bessel beam with non-diffractive properties show its large depth of focus advantage over Gaussian beam. Bessel beam can be generated by the axicon, which has high conversion efficiency. The non-diffraction distance and the main lobe size of the Bessel beam depend on the parameters of the axicon and incident light wavelength. We analyzed that the influence on the axial two-dimensional intensity distribution of a zero-order Bessel beam by changing the axicon parameters and the incident Gaussian beam size. Experimentally, the axicon with different parameters were fabricated using different materials. Then the two-dimensional intensity distribution of the Bessel beam in the axial and transverse direction were recorded and analyzed. The experimental results is basically consistent with the theoretical ones.

© (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Abstract-Encapsulated morphology measurement based on continuous-wave terahertz reflective off-axis digital holography

Yanlin Zhao, Dayong Wang, Lu Rong, Yunxin Wang, Jie Zhao, Zhihao Xu

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10826/1082616/Encapsulated-morphology-measurement-based-on-continuous-wave-terahertz-reflective-off/10.1117/12.2501115.short

Terahertz nondestructive testing is an increasingly important technology in recent years. Compared with visible and infrared bands, terahertz wave can easily penetrate common nonpolar and nonmetal materials without ironize the sample because of low energy. Digital holography can reconstruct the quantitative amplitude and phase distributions of the object wavefront. We proposed a continuous-wave terahertz reflective off-axis digital holography to measure the morphology of encapsulated object. An experimental system was built using a 2.52 THz (118.83 μm) far-infrared gas laser 295-FIR and a pyroelectric array detector. The morphology of the metallic bookmark hidden behind the optically opaque materials such as polytetrafluoroethylene and Polypropylene plates were obtained by angular spectrum integral and phase unwrapping algorithm. It proves that THz digital holography is an effective nondestructive testing method.

© (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Abstract-Application of continuous-wave terahertz computed tomography for the analysis of chicken bone structure

Bin Li,  Dayong Wang,  Lu Rong; Changchao Zhai, Yunxin Wang,  Jie Zhao

https://www.spiedigitallibrary.org/journals/Optical-Engineering/volume-57/issue-2/023105/Application-of-continuous-wave-terahertz-computed-tomography-for-the-analysis/10.1117/1.OE.57.2.023105.short

Terahertz (THz) radiation is able to penetrate many different types of nonpolar and nonmetallic materials without the damaging effects of x-rays. THz technology can be combined with computed tomography (CT) to form THz CT, which is an effective imaging method that is used to visualize the internal structure of a three-dimensional sample as cross-sectional images. Here, we reported an application of THz as the radiation source in CT imaging by replacing the x-rays. In this method, the sample cross section is scanned in all translation and rotation directions. Then, the projection data are reconstructed using a tomographic reconstruction algorithm. Two-dimensional (2-D) cross-sectional images of the chicken ulna were obtained through the continuous-wave (CW) THz CT system. Given by the difference of the THz absorption of different substances, the compact bone and spongy bone inside the chicken ulna are structurally distinguishable in the 2-D cross-sectional images. Using the filtered back projection algorithm, we reconstructed the projection data of the chicken ulna at different projection angle intervals and found that the artifacts and noise in the images are strikingly increased when the projection angle intervals become larger, reflected by the blurred boundary of the compact bone. The quality and fidelity of the 2-D cross-sectional images could be substantially improved by reducing the projection angle intervals. Our experimental data demonstrated a feasible application of the CW THz CT system in biological imaging.

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

Abstract-Synthetic aperture in terahertz in-line digital holography for resolution enhancement

Haochong Huang, Lu Rong, Dayong Wang, Weihua Li, Qinghua Deng, Bin Li, Yunxin Wang, Zhiqiang Zhan, Xuemin Wang, and Weidong Wu

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-55-3-A43&origin=search

Terahertz digital holography is a combination of terahertz technology and digital holography. In digital holography, the imaging resolution is the key parameter in determining the detailed quality of a reconstructed wavefront. In this paper, the synthetic aperture method is used in terahertz digital holography and the in-line arrangement is built to perform the detection. The resolved capability of previous terahertz digital holographic systems restricts this technique to meet the requirement of practical detection. In contrast, the experimental resolved power of the present method can reach 125 μm, which is the best resolution of terahertz digital holography to date. Furthermore, the basic detection of a biological specimen is conducted to show the practical application. In all, the results of the proposed method demonstrate the enhancement of experimental imaging resolution and that the amplitude and phase distributions of the fine structure of samples can be reconstructed by using terahertz digital holography.

© 2015 Optical Society of America

Abstract-Terahertz in-line digital holographic multiplane imaging method

Haochong Huang, Dayong Wang, Lu Rong, Yunxin Wang

Beijing Univ. of Technology (China)

Weihua Li

China Academy of Engineering Physics (China)

http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=2628165

Terahertz waves of which frequency spans from 0.1 to 10 THz bridge the gap between the infrared spectrum and microwaves. Owing to the special features of terahertz wave, such as penetrability and non-ionizing, terahertz imaging technique is a very significant and important method for inspections and detections. Digital holography can reconstruct the amplitude and phase distributions of a sample without scanning and it already has many successful applications in the area of visible and infrared light. The terahertz in-line digital holographic multi-plane imaging system which is presented in this paper is the combination of a continuous-wave terahertz source and the in-line scheme of digital holography. In order to observe a three dimensional (3D) shape sample only a portion of which appears in good focus, the autofocusing algorithm is brought to the data process. The synthetic aperture method is also applied to provide the high resolution imaging effect in the terahertz waveband. Both intrinsic twin images and defocused objective images confuse the quality of the image in an individual reconstructed plane. In order to solve this issue, phase retrieval iteration algorithm is used for the reconstruction. In addition, the reconstructed amplitude image in each plane multiplies the mask of which the threshold depends on the values of the autofocusing curve. A sample with simple artificial structure is observed which verifies that the present method is an authentic tool to acquire the multi-plane information of a target in terahertz waves. It can expect a wide application in terahertz defect detecting, terahertz medical inspection and other important areas in the future. 

© (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Abstract-Biological Imaging Application by Using Continuous-wave Terahertz In-line Digital Holography

Haochong Huang, Dayong Wang, Lu Rong, Bin Li, and Yunxin Wang

https://www.osapublishing.org/abstract.cfm?uri=OMP-2017-JTu4A.22

Continuous-wave terahertz in-line digital holography is a novel quantitative phase-contrast imaging approach. The exprimental verification confirms that the present method is an high resolution biological detection technique in terahertz wave.

© 2017 OSA

Abstract-Terahertz in-line digital holography of dragonfly hindwing: amplitude and phase reconstruction at enhanced resolution by extrapolation

Lu Rong, Tatiana Latychevskaia, Dayong Wang, Xun Zhou, Haochong Huang, Zeyu Li, and Yunxin Wang  »View Author Affiliations http://8.18.37.105/oe/abstract.cfm?uri=oe-22-14-17236

Optics Express, Vol. 22, Issue 14, pp. 17236-17245 (2014)
http://dx.doi.org/10.1364/OE.22.017236

We report here on terahertz (THz) digital holography on a biological specimen. A continuous-wave (CW) THz in-line holographic setup was built based on a 2.52 THz CO₂ pumped THz laser and a pyroelectric array detector. We introduced novel statistical method of obtaining true intensity values for the pyroelectric array detector’s pixels. Absorption and phase-shifting images of a dragonfly’s hindwing were reconstructed simultaneously from single in-line hologram. Furthermore, we applied phase retrieval routines to eliminate twin image and enhanced the resolution of the reconstructions by hologram extrapolation beyond the detector area. The finest observed features are 35 μm width cross veins.

© 2014 Optical Society of America

Abstract-Terahertz in-line digital holography of dragonfly hindwing: amplitude and phase reconstruction at enhanced resolution by extrapolation

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-22-14-17236

Lu Rong, Tatiana Latychevskaia, Dayong Wang, Xun Zhou, Haochong Huang, Zeyu Li, and Yunxin Wang  »View Author Affiliations

Optics Express, Vol. 22, Issue 14, pp. 17236-17245 (2014)
http://dx.doi.org/10.1364/OE.22.017236

We report here on terahertz (THz) digital holography on a biological specimen. A continuous-wave (CW) THz in-line holographic setup was built based on a 2.52 THz CO₂ pumped THz laser and a pyroelectric array detector. We introduced novel statistical method of obtaining true intensity values for the pyroelectric array detector’s pixels. Absorption and phase-shifting images of a dragonfly’s hindwing were reconstructed simultaneously from single in-line hologram. Furthermore, we applied phase retrieval routines to eliminate twin image and enhanced the resolution of the reconstructions by hologram extrapolation beyond the detector area. The finest observed features are 35 μm width cross veins.

© 2014 Optical Society of America