1. Anhui Xihua University, Hefei 230088, China
2. Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, China
3. Institute of Intelligent Machines, Chinese Academy of Sciences, Hefei 230031, China
4. Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Hefei 230031, China
5. Anhui Sanlian University, Hefei 230601, China
Abstract：The traditional Raman spectroscopy can only detect the surface information of the sample, or can only through the transparent surface detect the inner information of the sample, and it has same problems to get information of multilayer opaque sample or opaque packaging sample, such as searching for hidden explosives, identifying fake medicine with opaque package and non-invasive detection of bone disease, etc.. Spatially offset Raman Spectroscopy (SORS) is a new type of spectral detection technique, which can get information from opaque package non-invasively or gain information through surface layer to inner of the sample directly. This technology solves the problems mentioned above. Firstly, this paper introduced the principle of SORS in detail. The fundamental principle lies in the theory of photon migration. Between the focus point of the incident laser light source and the focus point of the collect lens there is a certain spatial distance offset ΔS from surface of the sample. When the laser light incident into the surface of sample, it will be stimulated or scatter broadband fluorescence by the surface of sample. One part of scattered light will reach to the inner of sample, and the photons of Raman scattered light from inner sample is easier to migrate than the photons of the surface of sample. The photons of Raman scattered light are returned to the surface of sample and collected by optical system after multiple scattering. Scattered light from different depths ΔH have different spatial distance offset ΔS after returning to the surface of sample.When the spatial distance offset ΔS is zero, the focus point of the incident laser light and the focus point of the collect lens are coincided where the density of photons is maximum, and the Raman signal collected by optical system are mostly from the surface of sample, and Raman signal of inner sample is submerged. When the spatial distance offset ΔS is not zero, the Raman signal from the surface of sample collected by optical system is attenuated quickly, but Raman signal of inner sample is attenuated more slowly than that from the sample surface, and this makes the proportion of inner sample more larger, so as to realize the Raman spectral separation. Then optical system will show us the Raman spectral from different depths of inner sample with multivariate data analysis method, and this Raman spectral is the Spatially offset Raman Spectroscopy(SORS). SORS has a good ability to suppress the interference of Raman and fluorescence spectra of surface materials, especially for the extraction of Raman spectra from substances under opaque packaging materials, so as to identify the target components quickly and non-invasively. Secondly, the characteristics of SORS technology are introduced. It is the derivative of Raman spectroscopy. Besides it has all the advantages of Raman spectroscopy, such as simple sample making, less water interference, less sample consumption, high sensitivity, etc.. It also has the special advantages of effectively suppressing the fluorescence, deep detection, non-invasive characteristics of nondestructive detecting and remote detection. These special advantages improved the intensity of Raman spectra effectively, reduced the user’s detection and production costs and also improved the personal safety of the inspectors. At the same time, this paper summarized and compared three existing working methods of SORS technology, standard SORS, inverse SORS and tilted SORS. The standard SORS technology can be used in non-contact remote sensing detection, and inverse SORS compared with the standard SORS has higher sensitivity and potential anti spectral distortion, and the incident light face and the effective spatial distance offset ΔS is controllable, and also avoid the sample overheating. Tilted SORS has a higher detection sensitivity of SORS, and the experimental device is easy to achieve. Then, based on a large number of research papers, the development and application of SORS technology combined with other technologies in chemical production, security inspection, biomedicine, archaeology, food safety, inspection and counterfeiting and national defense safety in recent years were reviewed. Finally, the existing problems of SORS technology are pointed out and the future prospects of the technology are also prospected.
Key words：Spatially offset Raman spectroscopy; Deep detection; Non-invasive detection; Chemical and medical treatment
[1] ZHAO Yan-ru, LI Xiao-li, XU Ning, et al(赵艳茹，李晓丽，徐 宁，等). Spectroscopy and Spectral Analysis(光谱学与光谱分析)，2017, 37(5): 1350.
[2] GAO Guo-ming, LI Xue，QIN Zong-ding, et al(高国明，李 雪，覃宗定，等). Acta Optica Sinica(光学学报)，2013, 33(2): 230002.
[3] HAN Xiao-zhen, GUO Zheng-ye, KANG Yan, et al(韩孝朕，郭正也，康 燕，等). Acta Optica Sinica(光学学报)，2015, 35(1): 130003.
[4] Everall N, Hahn T, Matousek P, et al. Applied Spectroscopy, 2001, 55(12): 1701.
[5] Everall N, Hahn T, Matousek P, et al. Applied Spectroscopy, 2004, 58(5): 591.
[6] Eliasson C, Matousek P. Analytical Chemistry, 2007, 79(4): 1696.
[7] FANG Xiao-qian, PENG Yan-kun, LI Yong-yu, et al(房晓倩，彭彦昆，李永玉，等). Acta Optica Sinica(光学学报)，2017, 37(9): 930001.
[8] JIANG Jie, LI Ming, ZHANG Jing, et al(姜 杰，李 明，张 静，等). The Journal of Light Scattering(光散射学报)，2013, 25(4): 367.
[9] ZHAO Xiao-hua, ZHANG Ji, TANG Xiu-zhang(张晓华，张 骥，汤秀章). Annual Report of China Institute of Atomic Energy(中国原子能科学研究院年报)，2013：124.
[10] Sundarajoo S, Izake E L, Olds W, et al. Journal of Raman Spectroscopy, 2013, 44: 949.
[11] Matthew D K, Majumder S K, Anita M J. Optics Letters, 2009, 34(7): 926.
[12] Matthew B, Loeffen P W, Matousek P. SPIE, 2010, 7838：783808.
[13] Loeffen P W, Maskall G, Bonthron S, et al. SPIE, 2011, 8018：80181E.
[14] Matthew B, Andrewsa D, Loeffen P, et al. Journal of Pharmaceutical and Biomedical Analysis, 2013, 76: 65.
[15] Botteon A, Conti C, Realini M, et al. Analytical Chemistry, 2017, 89: 792.
[16] Sowoidnich K, Churchwell J H, Buckley K, et al. SPIE, 2016, 9887：988719.
[17] Matousek P, Draper E R C, GoodshipA E, et al. Applied Spectroscopy, 2006, 60(7): 758.
[18] ZHAO Juan, PENG Yan-kun(赵 娟，彭彦昆). Journal of Agricultural Science and Technology(中国农业科技导报)，2015, 17(5): 33.
[19] ZHENG Xiang-quan, LIAO Xin, XU Yi, et al(郑祥权，廖 鑫，徐 溢，等). Chemical Journal of Chinese Univrsities(高等学校化学学报)，2017, 38(4): 575.
[20] Cletus B, Olds W, Izake E L, et al. Quantum Electronics Conference & Lasers & Electro-Optics, 2011: 1339.
[21] Zachhuber B, Gasser C, Chrysostom E H, et al. Analytical Chemistry, 2011, 83: 9438.
[22] Izake E L, Cletus B, Olds W, et al. Talanta, 2012, 94: 342.
[23] Matousek P, Clark I P, Draper E R C, et al. Applied Spectroscopy, 2005, 59(4): 393.
[24] Realini M, Botteon A, Conti C, et al. Analyst, 2016, 141: 3012.
[25] Matousek P. Applied Spectroscopy, 2006, 60(11): 1341.
[26] Pavel Matousek. Chemical Society Reviews, 2007, 36: 1292.
[27] Olds W J, Jaatinen E, Fredericks P, et al. Forensic Science International, 2011, 212: 69.
[28] Eliasson C, Macleod N A, Matousek P. Analytical Chemistry, 2007, 79(21): 8185.
[29] Hopkins R J, Pelfrey S H, Shand N C. Analyst, 2012, 137: 4408.
[30] Conti C, Realini M, Colombo C, et al. Analyst, 2015, 140: 8127.
[31] https://www.cobaltlight.com/library/view/31[EB/OL].
[32] Hargreaves M D, Matousek P. SPIE, 2009, 7486：74860B.
[33] https://www.cobaltlight.com/news/Insight100-achieves-ECAC-Standard-3-The-Highest-Standard-for-European-Airports[EB/OL].
[34] Stone N, Baker R, Rogers K, et al. Analyst, 2007, 132: 899.
[35] https://www.cobaltlight.com/news/cobalt-system-first-human-bone-disease-trial-plus-historical-bone-disease-studies[EB/OL].
[36] Ding H, Lu G J, West C, et al. SPIE, 2016, 9689：96894.
[37] Hargreaves M D, Macleod N A, Brewster V L, et al. Journal of Raman Spectroscopy, 2009, 40: 1875.
[38] Botteon A, Conti C, Realini M, et al. Analytical Chemistry, 2017, 89: 792.
[39] Conti C, Realini M, Colombo C, et al. Analytical Chemistry, 2015, 87: 5810.
[40] Qin J W, Chao K L, Kim M S, et al. SPIE, 2016, 9864：98640.
[41] Qin J W, Kim M S, Chao K L, et al. Food Control, 2017，75: 246.
[42] Olds W J, Sundarajoo S, Selby M, et al. Applied Spectroscopy, 2012, 66(5): 530.
[43] Loeffen P W, Maskall G, Bonthron S, et al. SPIE, 2016, 9995(99950D): 1.
[44] Guicheteau J, Hopkins R J. SPIE, 2016, 9824(98240G): 1.
[45] ZHANG Xiao-hua, ZHANG Ji, ZHANG Hai-feng, et al(张晓华，张 骥，张海峰，等). Atomic Energy Science and Technology(原子能科学技术)，2014，48(3): 518.
