The absorption coefficient, absorption and emission cross-sections of CdSxSe1-x/ZnS (core/shell) Quantum Dots (QDs) were determined by measuring absorption-emission spectra of the QDs with different composition ratio x. The absorption cross-section of QDs shows an increase with the increase of QD size, and shows a decrease with the x increase. In addition, CdS0.4Se0.6/ZnS QDs doped fibers are prepared in a solid fiber core of ultraviolet gel in the doping concentration of 0.1~5 mg/mL. The absorption decay rate of 473 nm laser pumped into the QDs doped fiber are measured for different doping concentrations. There is evidence to show that the absorption-decay rate and the cross-section are weakly associated with the doping concentration, and the photoluminescence-peak intensity of the doped fiber varies with the fiber length and the doping concentration. There is a saturating doping concentration and desired fiber length corresponding to the maximum photoluminescent intensity. The experimental results provide a support for development of CdSxSe1-x/ZnS-QDs doped photoelectronic devices in the future.
A simple and ultrasensitive detect method for mercury based on the assembly and disassembly of gold nanorods was proposed. When reduced glutathione(GSH) was added into gold nanorods colloidal solution, Au-S bond will formed on the surface of the gold nanorods. Meanwhile hydrogen bonding and electrostatic interaction prompt self-assembly of gold nanorods (End to End). After mixed with mercury ion, self-assembly of gold nanorods will be inhibition and re-dispersion. Based on above phenomenon, super lower concentration of mercury ion canbedetected used surface plasmon resonance (SPR) of gold nanorods. The lowest detection limit of this method is 1nmol/L when measured by UV-Vis spectroscopy, and the range is from 10 μmol/L to 100 μmol/L when observed by the naked eye. This method for mercury detection based on the assembly and disassembly of gold nanorods can be applied to detecting and monitoring of mercury in environmental.
A series of Tm3+/Yb3+ co-doped oxyfluoride tellurite glasses with various Tm3+ concentrations was synthesized via a conventional high temperature solid state method. Absorption spectra showed that Yb3+ and Tm3+ were successfully incorporated into the matrix. The sample exhibited strong 801 nm emissions corresponding to 3H4→3H6 transitions, with weak 476 and 651 emission respectively corresponding to the 1G4→3H6 and 1G4→3F4 transition.Concentration dependence of up conversion luminescence was analyzed and it was found that the optimal Tm2O3 concentration for achieving maximum upconversion emission intensity was 0.1%.Up conversion luminescence mechanism and concentration quenching were studied by emission spectra. Tm3+ ions obtained energy mainly comes from the energy transfer from Yb3+ to Tm3+. The concentration quenching was attributed to the nonradiative energy transfer through cross relaxation mechanism due to dipole-dipole interaction between Tm3+. Based on this rule, the possible energy transfer processes can be 1G4 + 3H6→3H5 + 3H4,1G4 + 3H6→3H4 + 3H5, 1G4 + 3H6→3F2,3+3F4 and 3H5+3H5→3H6+3F2. Additionally, the optical temperature sensing properties were investigated by using the thermal coupling 3F2,3 and 3H4 levels of Tm3+ under near infrared 980 nm excitation. The sample can be used as sensing material and better in high temperature sensitivity.
Based on the rst-principles plane-wave norm conserving pseudopotential of the spin-polarized density functional theory(DFT), we determined the U value of each atom for the Zn16O16 supercell via the method of generalized gradient approximation(GGA+U). The stability of the mixed structure is analyzed by calculating the formation energy and chemical bond Population. The energy band structure and the magnetic state of each doped structure is analyzed by calculating the atomic charge Population and spin electronic state density. Finally The effects of each rare earth element on the absorption spectrum of ZnO are discussed. The calculated results show that the lattice is expanded by the introduction of rare earth elements, the longest Zn-O bond increases and the shortest Zn-O bond decreases, which leads to distortion of oxygen tetrahedron. Y/La/Ce doped ZnO possesses ferrimagnetism, Th doped ZnO exhibits weak ferromagnetism, and Ac doped ZnO is paramagnetic body. Rare earth elements make the valence band and conduction band of ZnO down, make Fermi energy level enter the conduction band, and meanwhile enhance the conductivity of the system. The effect of Y/La/Ca doping on the ZnO band-gap is small, and the absorption spectrum is slightly blue-shifted, while visible light absorption coefficient of ZnO is effectively improved because Ce/Th is doped.
Ultraviolet/blue photodetector based on UMC 0.18μm CMOS technology is proposed, which is constructed by a lateral/vertical PN diode and an NMOS transistor. The shallow PN diode formed by the Twell layer and Nwell layer is used to enhanced the absorption efficiency of Ultraviolet/blue light and separate the photogenerated carriers. Since the gate of NMOS is tied with the Twell layer, it can be adjusted by the Twell voltage induced by the incident illumination. The sensitivity and the dynamic range of the proposed detector are improved. The simulation results show that the detector has extra high responsivity and wide dynamic range for the wavelength window of 300~550 nm. Under the condition of weak light (<1 μW/cm2), the detector has a responsivity more than 105 A/W. With the increase of light intensity, the responsivity decreases but it still better than 103 A/W in the interesting range.
A hydrogen sulfide gas sensor based on Cu-deposited graphene-coated tapered Photonic Crystal Fiber (PCF) Mach-Zehnder Interferometer (MZI) was proposed and fabricated. The PCF-MZI was formed by fusion splicing a PCF with length of 45 mm which was sandwiched between two Single-Mode Fibers (SMF), and the air holes of PCF in the splicing regions were fully collapsed, and then it could motivate the cladding modes better. Using isopropanol as dispersion agent, the monolayer powders of graphene were added in the solution and fully dispersed, and then the PCF was dip-coated and sintered repeatedly. Cu-deposited graphene-coated PCF was used to make the sensor produce high sensitivity. The results show that with the increasing concentration of hydrogen sulfide, the output wavelengths appear blue shift, and a high hydrogen sulfide gas sensitivity of 0.042 03 nm/ppm and good linear relationship are obtained within a measurement range from 0 to 60 ppm for hydrogen sulfide gas. The system has the advantages of low cost, high sensitivity and simple structure, especially suitable for low concentration and on-line monitoring of hydrogen sulfide gas.
One fluorescent aptasensor based on the fluorescence resonance energy transfer was constructed and used to detect insulin and dopamine. Aptamer labeled FAM (aptamer-FAM) was in charge of energy donor, while graphene oxide served as an energy acceptor. The results show that the linear detection range of insulin is from 0.05 μmol/L to 10 μmol/L and dopamine is from 1 μmol/L to 500 μmol/L, meanwhile the signal intensity of insulin is stronger than dopamine at the same concentration. The specificity experiments for insulin and dopamine have indicated that this fluorescent aptasensor have a good specificity. Due to its detection for different targets and high selectivity, this fluorescent aptasensor offers a promising prospect in the detection field of biological and medical.
Planar solar concentrator can provide dynamic concentration ratio, which has attracted researchers' attention.However, the decrease of the optical efficiency is not improved because of the rays-leakage from the lightguide.In order to hinder the decrease of optical efficiency from ray leakage, a new design method of the ray-leakage-free planar solar concentrator is proposed in this paper. According to the mathematical computation, refraction law and reflection law, the theoretical formula of the maximal ray-leakage-free propagating length in lightguide is derived. Furthermore, the mathematical model among the values of the parabola arbitrary coefficient,the vertex angle of air gap structure, the collector width, the collector height and the ray-leakage-free concentration ratio is established. The model of the proposed ray-leakage-free planar solar concentrator is simulated by the ray-tracing software. In consideration of Fresnel loss and material absorption, the concentration ratios of the proposed concentrators reach 698×, 857×and 1 032×with the corresponding optical efficiencies 88.2%, 85.3% and 80.2%, respectively, when the sunlight possess 0.27° divergence half angle; the concentration ratio increases further while the optical efficiency decreases slowly when the length of the lightguide exceeds the ray-leakage-free range.
A visible near infrared imaging spectrometer, which is mounted on the unmanned aerial vehicle, was designed for ground objects spectral analysis. The prism-grating-prism structure used in the spectrometer has the advantages of coaxial installation, small size and light weight. Objective lens with large field of view was designed through angular magnification selection, optical focal length distribution and relative aperture calculation. Initial spectral system structure was designed based on grating equation solution, volume phase holographic grating Bragg condition constraint and prism refraction law. The focal length of the objective lens was determined by the relationship between the emission angle and the detector width. The nonlinearity of the emission spectrum was shown by the exit light angle. The designed unmanned airborne imaging spectrometer has the spectral range of 400~1 000 nm and the filed angle of 40°. The transfer function value is greater than 0.67 in the whole spectral range at the cut-off frequency of 20.8lp/mm, and the spectral resolution is less than 3nm. An unmanned airborne imaging spectrometer was assembled for spectral push broom imaging experiments on trees outdoors,and the multi-spectral image of leaves was obtained. The imaging spectrometer can effectively realize spectral imaging, and has good performances.
Three-dimensional excitation-emission matrix fluorescence spectroscopy of Benzo[k] Fluoranthene (BkF), Benzo[b] Fluoranthene (BbF), and a mixture of these two substances were analyzed with FS920 fluorescence spectrometer. The results show that the fluorescence peaks of BkF can be observed at 306 nm/405 nm and 306 nm/430 nm, and the fluorescence peaks of BbF locate at 306 nm/410 nm and 306 nm/435 nm. In the mixture of BkF and BbF, concentration ratio and fluorescence interferences make excitation-emission matrix spectra of mixture change largely. Hence, the relationship between fluorescence intensity and concentration is complicated. In order to determine the concentration of BkF and BbF in mixture, radial basis function neural network optimized by hierarchical genetic algorithm was applied and the average recovery of BkF and BbF are 98.45% and 97.71%, respectively. The results showed that the possibility of the identification and concentration prediction of different components in mixed sample of polycyclic aromatic hydrocarbons.
The photosynthetic parameters can reflect the physiological state of plants. In order to obtain a more accurate fluorescence kinetic curve, a technique for measuring plant photosynthetic parameters based on the electron transfer process was proposed in this paper. Variable excitation light pulses was employed to devide the plant photosynthesis process into two stages:fast phase and relaxation phase, and corresponding fluorescence curves were induced for each stage. The excitation bandwidth and response time were analyzed using the TINA simulation tool. The I-V conversion and MFB filter were designed and simulated quantitatively. Synchronous sampling integral technique was employed to improve the SNR of weak relaxation phase fluorescence. As a result, a complete fluorescence kinetics curve that consist of fast phase and relaxation phase was obtained, from which the plant photosynthesis parameters can be calculated using nonlinear fitting algorithm. Experiment results showed that the system SNR reached 23.8 dB, and the correlation coefficients of measured Fv/Fm that obtained by this system were respectively 0.980 and 0.997 for dark and light adaptation conditions.
A polarization measurement method employing a Fiber Loop Ring-Down Spectroscopy (FLRDS) system is proposed and experimentally demonstrated. The influence of an Erbium-Doped Fiber Amplifier (EDFA) placed inside and outside the fiber ring on the pulse curve and the number of pulse peaks in the annular cavity is analyzed. A length of 2 m low-gain and low-noise erbium-doped fiber in EDFA is used to reduce waveform distortion and compensate for the attenuation of the cavity. Measurement of polarization angle θ was performed with the FLRDS system, and the change of θ is gained by recording the ring-down time τ of light pulse in the fiber loop. Results indicate that a good linear relationship is met between θ and τ in the range of 0°~90°. The sensitivity of the FLRDS system and the correlation coefficient of the fitted curve are 4.05 μs/° and 0.999 6, respectively. The maximum sensitivity error is 0.027 3. Through ten repeated experiments, six sets of data were selected to fit, and the average reproducibility error of the system was 0.030 8, and the repeatability was good, so it can be used in optical rotatory solution measurement, and also provides a reference for fiber radial stress birefringence and polarization state measurement of fiber lasers.
A set of beacon tracking servo system based on coarse-fine composite control was designed, which was aimed at demonstration test of space laser communication in atmospheric channel. Influence factors of tracking accuracy were analyzed and the impacts caused by atmospheric turbulence were researched in detail. A laboratory measurement system was constructed and the test about the effects of atmospheric turbulence on the optical spot tracking accuracy was completed. The results showed that the tracking accuracy was approximately linear with turbulent intensity increasing in weak-medium-strength atmospheric turbulence, which achieved spot tracking function well with a total system precision varied from 5 μrad to 15 μrad. An actual measurement for the tracking performance and accuracy of servo system was conducted in an air-air laser communication demonstration. The total tracking accuracy was no more than 15μrad and in accordance with the laboratory measurement system.
In order to remote sense the aerosol optical properties in the horizontal inhomogeneous atmosphere, a method based on twin scanning lidars was proposed for fine detection of aerosols. The scanning lidar was utilized to be the remote sensing tool to overcome the effect of overlap function of lidar system. The twin scanning lidars were performed for the cross scanning from the ground to the height of concern, which made the exact solutions of the two unknown parameters (extinction and backscatter coefficients) in the lidar equation retrievable. In the procedures of data retrieval, the coordinate and gridding were performed in the cross region, and the initial values of the pixel data were set. Numerical approximations of aerosol extinction and backscatter coefficients were got finally by minimizing the estimation of lidar function and the real one. The verification of retrieval method was performed using the scanning data from the long-range scanning lidar. The result shows that the retrieved result has the same tendency of height compared with the result from the multi-angle method, and twin scanning lidars can provide the aerosol distribution in cross scanning region profile which has advantage compared to the single profile.
A target signal phase self-correction method was proposed for Doppler asymmetric spatial heterodyne technique. First by sampling the interferogram frames of monochromatic light under different wind speed continuously, the phase drift was recorded. Then by fitting the phase curves at different speed and calculating the distance between two fitting lines, the phase drift was eliminated. The wind detection system was established in the laboratory to obtain the sampling interferogram and correct the phase error. The result shows that the error is up to 30.78 m/s at the wind speed of 60.37 m/s, and there is a great improvement after phase drift correction with a speed error of 3.51 m/s. Several groups of experiment under different wind speed were conducted and the wind speed was retrieved with a precision of 2.97 m/s finally.
Based on the extended Huygens-Fresnel principle and the unique cross spectrum density,the propagation properties of Gaussian non-uniformly partially coherent beams in turbulence atmosphere are studied synthetically. The results show that the abrupt change of the coherence distribution in the source plane disappear during the propagation in the turbulence atmosphere. During the propagation, the degree of coherence between two points first increase and then decrease with the increase of propagation distance. What's more, the non-uniform distribution of coherence in the source plane turns into uniform. Non-uniformly correlated partially coherent beams may have some applications in optical communication.
In order to realize the high precision measurement of indoor moving target pose, a pose measurement system based on laser projection imaging was established. The system used pairwise collinear and crossover arranged on the same plane point laser projector as the cooperation target, the motion target pose measurement baseline amplification system was made up of cooperation target and laser projection point receiving curtain. Then, the high speed camera was used to real-time recording curtain projection light spot, and the world coordinates of projection spots were solved by the camera calibration results, the moving target pose calculation model was established using a unit vector that formed between projection spots. Finally, according to the measurement principle of target pose, the error transform function of image coordinate extraction, the external calibration parameters of camera and the beam straightness were deduced. The experimental results shows that when the cameras field-of-view is around 14 000 mm×7 000 mm, the attitude angle measuring accuracy of measurement system is 1'(1δ), the position is 5mm, and the target pose measurement error transfer function calculation. To verify the accuracy of the target pose measurement method proposed in this paper and the error transfer model, it can satisfy the target pose high precision requirements.
An on-line three-dimensional measuring method based on speeded up robust features algorithm is proposed. Only one fixed sinusoidal grating is projected onto the moving measured object to guarantee the fringe direction perpendicular to the moving direction. While the object moves at the same spacing, the corresponding deformed patterns are captured by the CCD camera respectively. Then the background patterns can be extracted from the corresponding captured deformed patterns. With the aid of Speeded Up Robust Features(SURF)feature points matching algorithm on the background patterns, a group of equivalent phase shifting deformed patterns with the same shifting phase can be cut out. So the 3D surface of the online moving object can be reconstructed. The experimental results show the feasibility and effectiveness of the proposed method. Moreover, compared with the online Fourier Transform Profilometry (FTP)method, its average absolute error is less than one-half of that of the online FTP and its root mean square error is less than one quarter of that of the online FTP.
To address the limitation of existing unmannedaerialvehicle photoelectric localization method used for moving objects, this paper proposes an improved two-unmannedaerialvehicleintersection localization system based on airborne optoelectronic platforms by using the crossed-angle localization method of photoelectric theodolites for reference. This paper introduces the makeup and operating principle of intersection localization system, creates auxiliary coordinate systems, transforms the light of sight vectorsinto homogeneous coordinates, and establishes a two-unmannedaerialvehicle intersection localization model. In this paper, the influence of the positional relationship between unmannedaerialvehicles and the target on localization accuracy has been studied in details to obtain an ideal measuring position and the optimal localization positionwhere the optimal intersection angle is 69.984°. Given the optimal position, the localization root-mean-square error will be 38.043 4 m when the target is 20 km away fromunmannedaerialvehicle baselines. Finally, the influence of Kalman filtering on localization results is analyzed, and an appropriate filtering model is established to reduce the localization root-mean-square error to 13.584 2 m.
To research the feasibility, advantages and disadvantages of using white LED in collimation measurement, the comparison was conducted between collimated beams from a white LED and a LD, through comparative experiments of stability in intensity and positioning during a long-term work and the stability influenced by different air disturbance. The study found that the LD needs to preheat before working, and its intensity is unstable due to raising temperature inner the laser when working for long time, while the white LED beam can keep unchanged for long time without preheating. As a cool source, the white LED introduces less drift caused by deformation of mechanical structure resulting from heating. In research on influence of air disturbance, it shows that the white LED perfects not good as the LD. According to theoretical analysis on uniform temperature gradient field in air, and calculation results of beam drift with different wavelengths in white beam under the same disturbance, a beam with longer wavelength is less affected by disturbance. Thus the influence on the white beam is a weighted average of beams with different wavelengths and intensity, which is bigger than the influence on LD. Finally, the measurements of straightness errors of a linear guide using two collimated beams were conducted, which shows intensity distribution of the white LED beam keeps stable in propagation. Over all, the white LED has low cost, more stable intensity and less heating, and can be applied for collimation measurement.
In order to solve the problems of the linear response of the detector and the poor stability of the UV light source in the process of bidirectional reflectance distribution function bidirectional reflectance distribution function measurement of the far ultraviolet spectrum (140~240 nm) for solar diffuser, a relative method of measurement using the light source monitoring proportional compensation was proposed. According to the method, a system based on the structure of six-degree-free turntable was designed. The system can measure the bidirectional reflectance distribution function of the solar diffuser at any point and any position in the hemisphere space by controlling the diffuser with two-dimensional translation and rotation and the detector with two-dimensional rotation. The measurement experiment was carried out by using the proposed method, and the main factors that affect the measurement results of the system were analyzed. The total uncertainty of measurement is about 5.5%.
Based on the separation measurement theory of axial force,bending moment and torque in threaded pipe,the axial force,bending moment and torque of threaded pipe were measured by using Fiber Bragg Grating sensors.From the measured results,the axial force measured by fiber Bragg grating sensors is agreement with that by pressure sensor from driving motor,the error value is between -11.4 N and 15.5 N; the bending moment measured by Fiber Bragg Grating sensor is agreement with the theoretical value,the error value is between -0.54 N·m and 0.46 N·m; the torque measured by Fiber Bragg Grating sensor is agreement with that by torque sensor from driving motor,the error value is between -0.54 N·m and 0.87 N·m.The measured results verify the validity of measuring mechanical parameters for threaded pipe by Fiber Bragg Grating sensor. This technology provides a new method of mechanical parameters measurement for threaded pipe.
In order to improve the precision of celestial positioning system, and decrease the influence of the inclinometer installation error on the level measurement, the calibration and correction of the installation parameters of inclinometer in celestial positioning system were studied. First, the working principle of celestial positioning system based on inclinometer was presented, and the error sources in the installation process of inclinometer were analyzed. Then, a method for calibrating the installation parameters of inclinometer was proposed by transformation of celestial positioning system, and the correction algorithm of inclination measurement was presented. Finally, the simulation platform of three fields of view celestial positioning system was established, and the performance of the calibration method was analyzed and verified. Experimental results indicate that the calibration accuracy of the installation parameters of inclinometer is consistent with the accuracy of the sensor, and the maximum error of the inclination measurement is 4.315 5″ in full-range, which can satisfy the requirement of the high-precision level measurement of celestial positioning system.
Based on Zernike polynomials fitting, the measurement errors posed by optical axis deviation, rotation angle and active area on different types of high-precision surface were analyzed and the experimental verifications were conducted respectively. The results show that the measurement is not sensitive to the rotation angle and active area, the cost of calibrated rotation angle can therefore be reduced, while the impact of optical axis deviation on measurement precision is rather significant, which should be strictly adjusted before the test on high-precision surface.
Finite element analysis model of the conduction-cooled package high power semiconductor lasers were established respectively to analyze normal stress, shear stress and displacement in reflowing process and operating process independently. With the help of analytical solution model, the cause and the distribution of thermal stress and smile were analyzed. The results show that shear stress is the origin of other thermo-mechanical behavior in reflowing process due to coefficient thermal expansion mismatch, while both coefficient thermal expansion mismatch and temperature gradient affect the thermal stress and displacement in operating process. In order to obtain the accurate result, the residual stress and displacement of reflowing process were considered as the initial condition in operating finite element analysis simulation, and the thermal stress and smile were simulated. The influence of heat sink temperature on smile was studied with finite element analysis and experiment. The result shows operating process has great impact on smile and results in worse smile, and with the rising of temperature of heat sink, smile also becomes larger.
The model of the free vortex aerodynamic window with high pressure-ratio was established, and the whole flow field of the aerodynamic window was simulated. The result shows that there is no obvious wave through the export channel of the laser; with the contour of the free-vortex nozzle optimized, the shock wave behind the output of the free vortex nozzle disappeared, and the free-vortex jet flow field get better; with the boundary flow of the diffuser optimized, the total energy of the jet is heightened. The sealing pressure of the aerodynamic window is reduced from 37.5torr to 6torr. The results do effort to the free-vortex aerodynamic window's research and development.
In order to improve the dehazing effect of hazed image, a fast single-image dehazing method based on dark channel prior was proposed in allusion to the defect of dark channel prior rule. Based on the dark channel prior rule, the quad-tree search algorithm was adopted to estimate the value of atmospheric optical, which is used to simplify the atmospheric scattering model by the white balance. Then, the coarse estimation of medium transmission was obtained through the dark channel prior knowledge, and the guided filter and double-threshold judgment method were used to optimize the fringe and sky regions. Finally, the simplified atmospheric scattering model and tone mapping were adopted to get the dehazed image. Compared to some state-of-the-art methods, the proposed method can achieve a faster processing speed, effectively improve the definition of the dehazed image, and obtain good image color.
A hybrid optomechanical system consisting of an optical parametric amplifier and Coulomb force was proposed to observe the double optomechanically induced transparency (OMIT) by introducing the Coulomb coupling between the two nanomechanical resonators. The tunable characteristics of OMIT were studied under the resolved sideband regime and red detuning. The tunable double-OMIT can be observed from the output field at the probe frequency by controlling the intensity of the Coulomb coupling. The distance between the two transparency windows is increased symmetrically by enhancing the intensity of the Coulomb coupling. Changing the delays of two nanomechanical resonators can only bring about a slight influence on the depth of the double windows. The double-OMIT windows will broaden out only by enhancing nonlinear gain of the Optical Parametric Amplifier (OPA). A narrower transparency windows than the case of empty cavity can be realized by phase matching when the phase of the field driving the OPA was considered. These results might be applied to light storage and precision measurement.