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Characterizing PM2.5 in Beijing and Shanxi Province using terahertz radiation
Ning LI,Honglei ZHAN,Kun ZHAO,Zhenwei ZHANG,Chenyu LI,Cunlin ZHANG
Front. Optoelectron.. 2016, 9 (4): 544-548.
https://doi.org/10.1007/s12200-016-0608-1
Particles of aerodynamic diameter≤2.5 μm (PM2.5) caused extremely severe and persistent haze pollution is of concern in many cities. In this study, samples of PM2.5 were collected from atmosphere environment of Beijing and Shanxi Province, and analyzed using terahertz (THz) radiation. The transmission spectrum of PM2.5 in Shanxi Province had two distinct absorption peaks at 6.0 and 6.7 THz, and the curve was increasing on the whole. However, the transmission spectrum of PM2.5 in Beijing had obviously different variation tendency and the absorption peak was studied by monitoring PM2.5 masses in conjunction with two-dimensional correlation spectroscopy (2DCOS). By comparing the pollutant species and concentrations of Shanxi Province and Beijing over the time of collecting samples, the concentrations of sulfate and ammonium were similar, which contributed to emerge absorption bands in the same position. While the concentrations of organic matter (OM), nitrate, chloride and elemental carbon (EC) were different. Furthermore, dust and some other inorganic ion are unique to Shanxi province, which lead to different variation tendency of the transmission spectrum of PM2.5. These results will be of importance for environmental monitoring and for controlling PM emissions. According to this research, optical techniques, and especially spectral methods, should be considered for PM2.5 monitoring.
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Optical performance of ultra-thin silver films under the attenuated total reflection mode
Ming ZHOU,Sheng ZHOU,Gang CHEN,Yaopeng LI,Dingquan LIU
Front. Optoelectron.. 2016, 9 (4): 549-554.
https://doi.org/10.1007/s12200-016-0574-7
Ultra-thin silver films were deposited by thermal evaporation, and the dielectric functions of samples were simulated using Drude-Lorentz oscillators. When s-polarized incident light from the BK7 glass into thin silver film at 45° angle using attenuated total reflection (ATR) mode, we experimental observed that the reflection reach a minimum of 1.87% at 520 nm for thickness of d~6.3 nm silver film, and it reach a minimum of 10.1% at 500 nm for thickness of d~4.1 nm. Moreover, we simulated the absorption changes with incident angles at 520 nm for both p-polarized (TM wave) and s-polarized (TE wave) light using transfer matrix theory, and calculated the electric field distributions. The absorption as a function of incident angles of TM wave and TE wave showed different characteristics under ATR mode, TE wave reached the maximum absorption around the critical angle θc~41.1°, while TM wave reached the minimum absorption.
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Effect of excitation frequency on characteristics of mixture discharge in fast-axial-flow radio frequency-excited carbon dioxide laser
Heng ZHAO,Bo LI,Wenjin WANG,Yi HU,Youqin WANG
Front. Optoelectron.. 2016, 9 (4): 592-598.
https://doi.org/10.1007/s12200-015-0523-x
A one-dimensional fluid model has been used to describe the effect of radio frequency (RF) on the characteristics of carbon dioxide (CO2), nitrogen (N2) and helium (He) mixture discharge at 120 mbar in fast-axial-flow RF-excited CO2 laser. A finite difference method was applied to solve the one-dimensional fluid model. The simulation results show that the spatial distributions of electron density and current density rely strongly on the modulating driven frequency. When the excitation frequency changes from 5 to 45 MHz, the plasma discharge is always in mode. Moreover, as the excitation frequency increasing, the higher densities of and can be obtained, which is important to get higher excitation efficiency for the upper laser level.
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Off-axis three-mirror reflective zoom system based on freeform surface
Guijuan XIE,Jun CHANG,Ke ZHANG,Jide ZHOU,Yajun NIU
Front. Optoelectron.. 2016, 9 (4): 609-615.
https://doi.org/10.1007/s12200-015-0515-x
A reflective optical system is not affected by chromatic aberration, so it has a wide range of applications. Based on the design theory of reflective zoom system with three mirrors, this paper presents the simulation, optimization, and image quality evaluation of the traditional off-axis three-mirror zoom system and freeform off-axis three-mirror reflective zoom system.. In these systems, the optical design was aided by software CODEV. Through the analysis of aberrations and structural performance for the traditional aspherical off-axis three-mirror system, the freeform surface was introduced to the tertiary mirror to improve the balance capacity for optical aberrations. This off-axis three-mirror reflective zoom system based on freeform surface could provide technical reference to the study of such systems.
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Design of temperature insensitive in vivo strain sensor using multilayer single mode optical fiber
F. MAKOUEI,S. MAKOUEI
Front. Optoelectron.. 2016, 9 (4): 621-626.
https://doi.org/10.1007/s12200-016-0537-z
Bone strain measurement is a case of interest and demanding task for osteogenic adaption responses. In this paper, a novel biocompatible optical sensor for the bone axial strain measurement was proposed. In case modern multilayer single mode WII type optical fibers are well designed, they exhibit superior characteristics compared to conventional metal strain gauges (SGs). Furthermore, they could be strong competitors for SGs based on fiber Bragg grating (FBG) devices. In this study, mode field diameter (MFD) was selected as the indirect parameter for sensing task, which was totally a new approach. The strain sensitivity of 70.7733 pm/µε was obtained. Moreover, temperature sensitivity was –3.0031 × 10−6 pm/°C, which was negligible and removed the temperature compensation complexity for the sensor structure presented. The satisfactory property achieved for the designed sensor is as a result of multilayer fiber’s complicated structure as well as the design procedure based on evolutionary genetic algorithm (GA). In addition, the sensor demonstrated a reliable performance as its sensitivity was independent of the magnitude of the applied load.
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Hyperspectral image unmixing algorithm based on endmember-constrained nonnegative matrix factorization
Yan ZHAO,Zhen ZHOU,Donghui WANG,Yicheng HUANG,Minghua YU
Front. Optoelectron.. 2016, 9 (4): 627-632.
https://doi.org/10.1007/s12200-016-0647-7
The objective function of classical nonnegative matrix factorization (NMF) is non-convexity, which affects the obtaining of optimal solutions. In this paper, we proposed a NMF algorithm, and this algorithm was based on the constraint of endmember spectral correlation minimization and endmember spectral difference maximization. The size of endmember spectral overall-correlation was measured by the correlation function, and correlation function was defined as the sum of the absolute values of every two correlation coefficient between the spectra. In the difference constraint of the endmember spectra, the mutation of matrix trace was slowed down by introducing the natural logarithm function. Combining the image decomposition error with the influences of endmember spectra, in the objective function the projection gradient was used to achieve NMF. The effectiveness of algorithm was verified by the simulated hyperspectral images and real hyperspectral images.
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16 articles
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