Abstract-Resolution Enhancement in Terahertz Imaging via Deconvolution

Wei Ning, Feng Qi, Zhaoyang Liu,  Yelong Wang, Hongming Wu, Jinkuan Wang

https://ieeexplore.ieee.org/document/8717628

Nowadays, terahertz (THz) imaging is quite promising in scientific and biomedical applications. However, the much longer wavelength degrades the resolution of obtained images compared with classical imaging at optical frequencies. Imaging is considered to be a convolution process between the object function and point spread function (PSF) of the system. Thus, how to describe the object accurately from a blurred image is an inverse problem. In this paper, we demonstrate how well such a method can function. We would illustrate how to make current facilities overcome the physical limitations in imaging, which can image at the sub-spot level. Periodical stripes with a period of 0.8 mm are resolved at 0.3 THz. The resolution is 0.32 times the physical size of the focused beam. Moreover, this method is extended to the mathematical operations in a complex domain, which is distinct from previous image studies via visible/IR light. Physically, it means that we essentially deal with phase by making use of the wave nature of THz light. For the first time, it is demonstrated that the reconstructed phase can also describe the shape of the object by applying such an approach. In addition, we have successfully measured the diameter of human hair with a relative error of less than 10% at 3 THz. As an example, we did an experiment on tissues of colorectal cancer and a better image is obtained, which would be helpful for medical diagnosis. We believe that such an approach is able to improve imaging performance at THz frequencies and many applications will gain from it.

Abstract-Wideband Method to Enhance the Terahertz Penetration in Human Skin Based on a 3-D Printed Dielectric Rod Waveguide

Yelong Wang   Feng Qi, Zhaoyang Liu,  Pengxiang Liu, Weifan Li, Hongming Wu,  Wei Ning

https://ieeexplore.ieee.org/document/8610236

In this paper, a wideband method based on a three-dimensional (3-D) printed dielectric rod waveguide (DRW) is proposed to enhance the terahertz (THz) penetration in the human skin. Two skin models are established to mimic the electromagnetic environments in the hydrated and dehydrated skin tissue, and the characteristics of the DRW are analyzed in detail. Three human tissues embedded in paraffin are measured to test the performance of the DRW. Experimental results demonstrate that the DRW generates an average penetration enhancement of 28% from 140 to 220 GHz compared with the conventional waveguide, which is rather close to the simulation prediction. Meanwhile, the DRW can significantly increase the dynamic range of the reflection signal from the skin tissue, which is meaningful in clinical application. The design of the DRW described here can be easily applied to other THz band, and the 3-D printing technique makes the fabrication flexible.

Abstract-Low-threshold terahertz-wave generation based on a cavity phase-matched parametric process in a Fabry–Perot microresonator

Pengxiang Liu, Feng Qi, Weifan Li, Yelong Wang, Zhaoyang Liu, Hongming Wu, Wei Ning, Wei Shi, and Jianquan Yao

https://www.osapublishing.org/josab/abstract.cfm?uri=josab-35-1-68&origin=search

A configuration for an optical pumped monochromatic terahertz (THz) source operating in a high repetition rate is developed and based on a resonant parametric process within a Fabry–Perot microcavity. Comprehensive analysis of the spectral selection, cavity phase matching, energy-conversion dynamic, and input–output characteristics is provided. Calculations are performed on a Tm3+${\mathrm{Tm}}^{3+}$-doped fiber laser pumped GaAs sheet. It is indicated that a pump threshold can be scaled down by injection seeding of the signal wave. Efficient THz wave generation (mW level average power) under relatively low pump peak power (65 kW) is predicted.

© 2017 Optical Society of America