Abstract：A new method of terahertz (THz) imaging based on the mean absorption is proposed. Terahertz radiation is an electromagnetic radiation in the range between millimeter waves and far infrared. THz pulse imaging emerges as a novel tool in many fields because of its low energy and non-ionizing character, such as material, chemical, biological medicine and food safety. A character of THz imaging technique is it can get large amount of information. How to extract the useful parameter from the large amount of information and reconstruct sample’s image is a key technology in THz imaging. Some efforts have been done for advanced visualization methods to extract the information of interest from the raw data. Both time domain and frequency domain visualization methods can be applied to extract information on the physical properties of samples from THz imaging raw data. The process of extracting useful parameter from raw data of the new method based on the mean absorption was given in this article. This method relates to the sample absorption and thickness, it delivers good signal to noise ratio in the images, and the dispersion effects are cancelled. A paper with a “THz” shape hole was taken as the sample to do the experiment. Traditional THz amplitude imaging methods in time domain and frequency domain are used to achieve the sample’s image, such as relative reduction of pulse maximum imaging method, relative power loss imaging method, and relative power loss at specific frequency imaging method. The sample’s information that reflected by these methods and the characteristics of these methods are discussed. The method base on the mean absorption within a certain frequency is also used to reconstruct sample’s image. The experimental results show that this new method can well reflect the true information of the sample. And it can achieve a clearer image than the other traditional THz amplitude imaging methods. All the experimental results and theoretical analyses indicate that the method base on the mean absorption within a certain frequency can reflects sample absorb and thickness information, it can achieve good signal to noise ratio in the images. Because the absorption is mean absorption within in a certain frequency, so the method proposed in this article is especially suitable for samples with simple structure. And this new method can be a useful added tool for the other traditional THz amplitude imaging methods.
[1] Hu B B, Nuss M C. Opt. Lett., 1995, 20(16): 1716. [2] Wang S, Zhang X C. J. Phys. D: Appl. Phys., 2004, 37: R1. [3] Jelena Obradovic, James H P Collins, Ole Hirsch, et al. Polymer, 2007, 48: 3494. [4] Beard M C, Turner G M, Schmuttenmaer C A. Phys. Med. Biol., 2002, 47: 3841. [5] Sun Wenfeng, Wang Xinke, Zhang Yan. Optik, 2012, 123: 1980. [6] Paul Dean, Alex Valavanis, James Keeley, et al. Appl. Phys. Lett., 2013, 103: 181112. [7] Chen Q, Jiang Z P, Xu G X, et al. Opt. Lett., 2000, 25(15): 1122. [8] Federici J, Mitrofanov O, Lee M, et al. Phys. Med. Biol., 2002, 47: 3727. [9] Kiwon Moon, Youngwoong Do, Meehyun Lim, et al. Appl. Phys. Lett., 2012, 101: 011109. [10] Leila H Eadie, Caroline B Reid, Anthony J Fitzgerald, et al. Expert Syst. Appl., 2013, 40: 2043. [11] Ashish Y Pawar, Deepak D Sonawane, Kiran B Erande, et al. Drug Invention Today, 2013, 5(2): 157. [12] Paul M J, Tomaino J L, Kevek J W, et al. Appl. Phys. Lett., 2012, 101: 091109. [13] Pradarutti B, Mattha¨us G, Riehemann S, et al. Opt. Commun., 2007, 279 : 248. [14] ZHANG Zhen-wei, CUI Wei-li, ZHANG Yang, et al(张振伟，崔伟丽，张 岩，等). J. Infrared Mmim Waves(红外与毫米波学报), 2006, 25(3): 217. [15] Xi Zaijun, Xiao Tiqiao, Zhang Zengyan，et al. Chin. Phys. Lett., 2006, 23(2)：352. [16] Zhang Zengyan, Yu Xiaohan, Zhao Hongwei, et al. Opt. Commun., 2007, 277: 273.
