1. The Light Scattering of particles: Theory and Applications
Scattering occurs when the light passes through particles. The intensity distribution, polarization and spectral characteristics of the scattering field are all related to the characteristics of the scattering body. By measuring the scattered light, a wide variety of information about the structure and property of the scattering body can be acquired.
Based on the theories of light scattering, a large number of optical measurement techniques have been developed, such as Phase Doppler, spectroscopy, Rainbow Refractometry and Small Particle Imaging Techniques. They have found wide applications in multiphase flow, combustion processes, optical manipulation of small particles and other fields.
Figure 1. Typical scatterers: biological cells, nanoparticles, and fuel particles
Our research group has good research basis in Mie theory, Debyseries, T-matrix, GOA (Geometrical-Optics Approximation), VCRM (Vector Complex Ray Model) and other algorithms for light scattering, and published a number of high-quality academic papers. We keep a long-term close cooperative relationship with Prof. Ren Kuan Fang from the CORIA Institute of Rouen University in France. Prof. Ren Kuan Fang developed the vector complex ray model (VCRM) which can be used to describe the scattering properties of objects of arbitrary shape, so that our group can follow the international frontier.
Figure 2. Wavefront Interaction in Vector Complex Ray Model (VCRM)
Figure 3. Light scattering of large elliptical cylinders (Ray tracing and VCRM results)
Figure 4. Double prime rainbows of coated cylinder(Ray tracing and Debye calculation results)
Figure 3 shows the calculation results of the light scattering based on VCRM for large-size, large ellipsoid ratio, and oblique elliptical cylinder. We proposed Debye scattering model and algorithm for the inhomogeneous spherical particle which provide a powerful numerical tool for the analysis of the light scattering mechanism and the study of the scattering properties of large-scale non-homogeneous spherical cylindrical particles. The twin rainbows of a coated cylinder are shown in figure 4.
The rainbow refractometry has the advantages of high sensitivity, high accuracy and low cost. Among several configurations of rainbow refractometry, that base on the Ripple structure rainbow has been developed in the Ph.D. thesis of X. Han, which permits to measure small changes in diameter and temperature. For a particle of 1mm, the diameter measurement accuracy is in the micrometer range, and the measurement accuracy of the diameter variation can reach the nanometer level.
Figure 5. The variation of the phase difference of first-order rainbow intensity distribution with the diameter of spherical particles
Figure 6. Laser rainbow measurement experiment system for liquid jets
Figure 7. Light rays scattered by a circular jet
We have applied the rainbow refractometry in the study of the photothermal effect of Au nano-particles. the accuracy of temperature and temperature variation measurement are better than 0.1℃ and 1℃, respectively.
Figure 8. First and second rainbows of the liquid particle containing Au nanoparticle solutions
Figure 9. Au nanoparticle droplet temperature changes with time
At present, some of the research work focuses on the study of the light scattering properties of liquid jets, and it is hoped that laser rainbow measurements can be used to measure the geometrical/temperature evolution characteristics of the jets in real time without contact. In addition, the research team is working on the high speed high-accuracy measurement of evaporation rate of liquid drops.
Part of our research achievements：
[1] Qingwei Duan, Ruliang Zhong, Xiang'e Han, Kuan Fang Ren, Influence of spatial curvature of a liquid jet on the rainbow positions: Ray tracing and experimental study, JQSRT, 2017, 195, 156-163,
[2] K. Jiang, X. Han, and K. F. Ren, “Scattering of a Gaussian beam by an elliptical cylinderusing the vectorial complex ray model”, Opt. Soc. Am. A, 2013, 30, 1548-1556 .
[3] Li R, Ren K F, Han X, et al. Analysis of radiation pressure force exerted on a biological cell induced by high-order Bessel beams using Debye series[J]. JQSRT, 2013, 126: 69-77.
[3] Keli Jiang, Xiang’e HAN, and Kuan Fang Ren. Scattering from an elliptical cylinder by using the vectorial complex ray model. Appl. Opt, 2012, 51(34): 8159-8168.
[4] Renxian Li, Xiang’e Han, et al. Debye series for light scattering by a multilayered sphere. Applied Optics. 45(6),2006, PP:1260-1270
2. Research on light scattering of gold nanoparticles
The unique optical properties of metal nanoparticles are related to their localized surface plasmon resonance(LSPR) which leads to enhanced absorption and scattering of light at the resonant wavelength, and are widely used in mutiple fields of biomedical, chemical catalysis, information storage, energy and environmental sciences. The size and concentration of gold nanoparticles are two key parameters which determine the properties of LSPR. Therefore, it is crucial to precisely measuring them in preparation, characterization and application of the gold nanoparticles.
Figure 10. Samples of gold nanoparticles.
The size and concentration are two important parameters of gold nanoparticle, which are not only directly affects the optical properties of the particle, but also determines the properties and behavior of gold nanoparticles in the practical applications. Thus, the accurate measurement of size and concentration is critical for the preparation, characterizationand applications of gold nanoparticles.The extinction spectroscopy is a simple fast, and can obtain information on size and concentration of particles at the same time.
We have apptied the developped theortical and numerical foots on small particle light scattering T-matrix, Mie theory, DDA algorithm in the study of the optical properties of gold nanoparticles.
Figure 11. (a)Geometric model of gold nanospheres;
(b)Volumetric Backscattering and Absorption Coefficients of Au Nanospheres Change with Size
The extinction specrromerry system has been estabished in labsratory, and applied to the measurement of poty dispersed gold nanoparticles. The inversion results validate the reliability of the measursement system of the inversion algorithm.
Figure 12. The self-designed extinction spectroscopy system
Figure 13. The results of size distribution of the gold nanoparticle samples using extinction spectroscopy.
The absorption and scattering optical properties of non-spherical nanoparticles, such as gold nano-ellipsoids, cylinders, and nanorods, have also been studied.The research provides a theoretical basis to develop inversion tools for the study of two-dimensional scale distribution and concentration distribution measurement of non-spherical nanoparticles.
Figure 14. Geometric model of gold nanorods
Figure 15. Extinction characteristics and scattering characteristics of gold nanorods of different sizes
Based on the inversion method for the size and concentration distribution of gold nanospheres, the research group carried out research on the measurement methods of the size (diameter and length) distribution and concentration distribution of gold nanorods, and based on experimental measurements of the absorption spectrum of gold nanorods, inversion was performed. The concentration and size distribution of gold nanorods, preliminary inversion results show that the method has a good potential for development.
Figure 16. Extinction spectrum and size distribution of gold nanorods
Table 1. Results of inversion of particle size and concentration of Au nanoparticles
At present, the research work focuses on the experimental method and algorithm improvement of the simultaneous inversion of the two-dimensional size distribution and concentration distribution of gold nanorods, which is expected to be achieved through the combination of extinction spectrum and scattering spectrum. In addition, the study of the optical properties of a variety of complex shapes of gold nanoparticles remains to be carried out.
Part of our research achievements：
[1] Paerhatijiang Tuersun and Xiang’e Han. Optical absorption analysis and optimization of gold nanoshells [J]. Applied Optics, 2013, 52(6): 1325-1329.
[2] Paerhatijiang Tuersun and Xiang’e Han. Optimal dimensions of gold nanoshells for light backscattering and absorption based applications [J]. Journal of Quantitative Spectroscopy & Radiative Transfer, 2014, 146: 468-474.
[3] Paerhatijiang Tuersun and Xiang’e Han. Optimal design of gold nanoshells for optical imaging and photothermal therapy [J]. Optik, 2014, 125(14): 3702-3706.
[4] Han Xiang'e, Liu ying, Paerhatijiang Tuersun. Measurement of size and concentration of gold nanorods by spectral extinction method[J]. LIP2016,Apr. 22-26, 2016,
[5] Liu ying, Han Xiange, Chen jun. Optical properties and optimization of Au nanorods[C]. CSQRWC2015, Xi'an, China, August 12-15, 2015.
