In this work, a biosensing method based on in situ, fast, and sensitive measurements of ellipsometric parameters (Ψ, ∆) is proposed. Bare silicon wafer substrate is functionalized and used to bind biomolecules in the solution. Coupled with a 45° dual-drive symmetric photoelastic modulator-based ellipsometry, the parameters Ψ and ∆ of biolayer arising due to biomolecular interactions are determined directly, and the refractive index (RI) of the solution and the effective thickness and surface mass density of the biolayer for various interaction time can be further monitored simultaneously. To illustrate the performance of the biosensing method, immunosensing for immunoglobulin G (IgG) was taken as a case study. The experiment results show that the biosensor response of the limit of detection for IgG is 15 ng/mL, and the data collection time is in milliseconds. Moreover, the method demonstrates a good specificity. Such technique is a promising candidate in developing a novel sensor which can realize fast and sensitive, label-free, easy operation, and cost-effective biosensing.
In order to evaluate the node importance in complex network, considering the disadvantages of node deletion method, node contraction method and betweenness method, through defining the node efficiency and the node importance evaluation matrix, a method to find the vital node in complex networks is proposed by using the node importance evaluation matrix. Considered in this method are the node efficiency, node degree and adjacent node importance contributions, and used adjacent node degree and efficiency value to characterize the contribution of their importance. Finally, an optimized algorithm whose time complexity was O(Rn2) is provided. Experiments show that this method is effective and feasible, and it is applicable to large scale complex networks.
In order to achieve all Stokes parameters of spectral image with high spectral resolution, high spatial resolution, high polarization accuracy, high signal-to-noise ratio and good stability, taking into account the orthogonal characteristic of ±1 order diffraction light which diffracts from a acousto-optic tunable filter (AOTF), a new technique of full polarization hyperspectral imaging is presented. It uses one AOTF to diffract the incident light, one liquid crystal variable retarder (LCVR) to modulate the light retardation, and two CCDs to image the ±1 order diffraction light, respectively. According to the Muller matrixes of all optical elements in the system, the basic working principle of the new technique is that LCVR sequentially provides the retardation 2π, 1.5π, π and 0.5π for each spectral channel, so the CCD obtains corresponding images. After analyzing these images, the all Stokes parameters are obtained; the precision of this system for polarization imaging is determined mainly by polarization modulation device LCVR. Considering the azimuth of LCVR fast axis and retardation precision at the same time, it is unveiled that LCVR has no effect on the accuracy of the first Stokes parameter, and the relative errors of other latter 3 Stokes parameters are less than 0.064%, 0.31% and 3.97%; then, our prototype system is used to do the outdoor experiments in a summer sunny morning, images data for 26 spectral channels with spectral bandwidth of 10 nm, which are from 450 nm to 700 nm, are acquired, the imaging quality is very fine. Firstly, LCVR are not assembled in our prototype system, and AOTF works in the sweeping frequency mode. The spectrum from each CCD proves that the diffraction efficiency of AOTF ± 1 order diffraction light is not completely the same, and the difference must be considered in polarized image processing. Then another experiment is done after LCVR has been assembled. The image data of the incident light of 600 nm are taken for example to discuss its all Stokes parameters in detail. The results show that the principle of the new technique is correct and the new scheme is feasible. This study provides a new theory and implementation scheme for the polarization spectral imaging technology.
Recently, ellipsometry and polarization imaging using photoelastic modulators (PEMs) have been applied to a wide spectral range, from vacuum ultraviolet to the mid-infrared wavelengths. To ensure high accuracy polarization performance, the accurate calibration of the retardation of PEM is crucial. In this report, the dispersion of the retardation of the PEM is studied. According to the operational principle of PEM, their retardation can be separated into independent dispersion and driving terms. The effect attributed to the dispersion on PEM retardation calibration is experimentally explored. These experiments indicate that the dispersion term can be defined in advance using the refractive index of the photoelastic crystal under incident light, and that the driving term is directly proportional to the amplitude of the driving voltage. The calibration method for the retardation amplitude of the PEM, which considers dispersion, is also demonstrated. The results show that the relative deviation between the calibration and actual measurement values of PEM retardation amplitude are less than 1%. This study presents an accurate way to calibrate the PEM retardation and supports the application of PEMs in a wide range of wavelengths.
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