The homogeneity principle requires that the electron wave function must satisfy the condition of exchange antisymmetry. In view of its influence on the transient absorption spectrum of multi-electron system, the helium atom wave function with identical anti-symmetry is obtained by Ritz variational method. On this basis, the transient absorption spectra of attosecond extreme ultraviolet (XUV) light of helium atoms are studied theoretically by solving the three energy level model and comparing with the old model without considering electron exchange. This study breaks through the traditional single-electron transition model and focuses on the effect of electron exchange on the transient absorption spectrum of XUV light. It is found that the exchange interaction has an important influence on the physical quantities, such as the intensity of the transient absorption spectrum and the position of the absorption peak. The results can provide a reference for using transient absorption spectrum to detect the ultrafast correlation dynamics of electrons in atoms.

For the needs of military and civilian applications such as microwave communications, over-the-horizon radar, and cable television (CATV) systems, a homodyne coherent microwave photonic transmission link technology based on optical phase-locked loop and particle swarm optimization is proposed to realize high dynamic range and long-distance transmission of optical radio frequency (RF) signal. At the front end of the link, the homodyne optical phase-locked loop was used to realize the phase tracking and locking of the local oscillator light to the signal light, which can suppress the laser frequency drift and phase noise and the phase noise deterioration caused by long optical fiber within the lock-in bandwidth. Meanwhile, the balanced detection eliminates relative intensity noise related to direct current (DC) components. In addition, by analyzing the source of nonlinear distortion at the front end of the link, we utilized particle swarm optimization to search for the optimal nonlinear distortion correction coefficients in the digital processing unit at the back end, and performed delay matching, amplitude and phase equalization, and linear phase demodulation for the I/Q digital signals. The high dynamic range and long-distance (≥120 dB·Hz 2/3 and 100.8 km) transmission of RF signals within 100 MHz frequency band is realized.

In recent years, indoor localization algorithms have attracted a great deal of attention and research interest. For the improvement of the complexity as well as the accuracy of existing localization algorithms, this paper proposes a visible light indoor localization algorithm that first uses Elman neural networks for indoor localization prediction and then uses the weighted K-nearest neighbor (WKNN) algorithm to correct the prediction results. The algorithm is applied in an indoor localization system with a single LED as a transmitter and four horizontal photoelectric detectors (PDs) as receivers. The four horizontal PDs are located at the four corners of the receiver and the position to be measured is located at the center of the receiver. The initial position of the point to be measured is first determined by predicting the horizontal and vertical coordinates of the point by two Elman neural networks. Then the point to be measured with a positioning error greater than the average error predicted by the neural network prediction is identified and corrected with the WKNN algorithm to determine the exact position of the point to be measured, and the corrected position is updated into the overall position of the point to be measured. The simulation results show that the average positioning error of this algorithm is 7.13 cm and the average positioning time is 0.24 s in an indoor environment of 3.6 m×3.6 m×3 m.

In order to reduce the construction cost of a compound multi-surface concentrator and improve its utilization efficiency of solar energy, the single-layer glass tube embedded absorber is selected as the photothermal conversion component of a compound multi-surface concentrator. The influence mechanism of the absorbers with different shapes in the single-layer glass tube on the photothermal performance of a compound multi-surface concentrator is mainly studied. First, the optical model of the concentrator is established in the optical simulation software TracePro, and the influence mechanism of absorber shapes on the optical performance of the concentrator is simulated and analyzed based on the Monte Carlo algorithm. Then, the influence of absorber shapes on the outlet temperature, instantaneous heating collection and photothermal conversion efficiency of the concentrator are analyzed. The results show that under the same incident angle, the number of light received by the “*”-shaped absorber is more than that received by the rectangular mesh receiver. When the incident angle is in the range of 0°--20°, the average light receiving rate and the average concentrating efficiency of the concentrator embedded with the“*”-shaped absorber are 7.37% and 6.66% higher than that of concentrator embedded with the rectangular mesh receiver, respectively. Under sunny weather conditions, the average outlet temperature, average discrepancy between air temperature of inlet and outlet, average instantaneous heating collection and average photothermal conversion efficiency of the concentrator embedded with “*”-shaped receiver are 48.5 ℃, 23.2 ℃, 467.5 W and 54.85%, respectively, which are 43.07%, 31.82%, 29.83% and 24.52% higher than that of the rectangular mesh receiver, respectively.

Present three-dimensional (3D) display systems based on integral imaging have small field of view and low resolution of reconstructed images. To overcome these limitations, a flexible microlens array structure with different numerical apertures suitable for curved integral imaging 3D display is designed and successfully built on curved screen. The optical simulation software of Trace Pro is used to establish a curved integral imaging 3D display system model. Further, the influence of the numerical aperture of the microlens on the reconstruction performance of the curved integral imaging 3D display system is investigated. The results show that for microlens with a constant size and thickness, the larger the numerical aperture, the better the quality of the reconstructed image and larger the field of view. However, if the numerical aperture of the flexible microlens array is 0.376, the reconstructed image will have a higher resolution. Moreover, when the field of view reaches 60°, the reconstructed image is still clear. For simulation verification, flexible microlens arrays with different numerical apertures are prepared and a prototype of the curved integral imaging system is constructed. The experimental results are consistent with the simulation results.

Aiming at the effective embedding and extraction of multi-watermarking information, an adaptive multi-watermarking algorithm based on peak signal-noise ratio-normalized correlation coefficient function (PSNR-NC) optimization and undecimated dual tree complex wavelet transform is proposed. First, the algorithm uses the PSNR-NC function to determine the best embedding position of the watermark. Then, multiple independent watermarks are embedded into the color host image by the unsampled double tree complex wavelet transform-singular value decomposition (UDTCWT-SVD) algorithm. Finally, the watermark extraction algorithm is used to extract multiple watermarks in the watermarked image, which effectively realizes the embedding and extraction of multiple copyright information. The experimental results show that the embedded watermark image has good invisibility, and the proposed algorithm is robust to common image processing attacks, especially in resisting JPEG compression, noise attacks and filtering attacks.

Because the rotating laser scanning measurement system adopts the instrument structure of separate receiver and transmitter, it is easy to be restricted by the complex measurement conditions in the industrial field. Aiming at the problem of limited adaptability of the system in the field, a single-station passive multi-target location method based on rotating laser scanning is proposed. In the proposed method, multiple cube-corner prisms are introduced as passive targets to be measured. The combination of signal transmitter and receiver is realized by constructing aspheric reflection receiving model, and the signal delay in this measurement mode is analyzed and compared. Moreover, a multi-target optical signal matching mechanism is established to realize passive multi-target rendezvous location. Finally, the experimental verification is carried out on the platform of workshop Measurement Positioning System. The results show that the proposed method can achieve sub-millimeter positioning accuracy in three directions within 10 m measurement range, and effectively improve the adaptability of rotating laser scanning measurement system in complex measurement environment.

White-light interferometry has the advantages of high accuracy and non-contact measurement, which is an important measurement method in the field of ultra-precision machining. To tackle the problem that white-light interferometry is easily affected by environmental vibration, dynamic vertical scanning interferometry (DVSI) is proposed. This method divides the white-light interferometric optical path into two imaging channels to generate a quasi-monochromatic light interferogram, which is phase-shifted synchronously with the white-light interferogram. We obtain the actual phase-shift scanning position by processing the quasi-monochromatic light interferogram through the phase-tilt iteration (PTI), after which the coherence peak of the white-light interference signal is located and the coarse topographic distribution is calculated. The local least square (LLS) is used to calculate the fine phase distribution. The coarse topographic distribution and fine phase distribution are combined to recover the three-dimensional topography of the tested sample. The method is verified through numerical simulation and experimental comparison, and the results show that the method has good vibration-resistant performance.

The proposed transmissive display dual-screen deflectometric system solves the challenging problem that traditional methods fail to obtain the three-dimensional (3D) shape of a mirror object with a discontinuous surface. The usage of a transparent display screen not only widens the measurement field of view but also reduces the complexity of the system structure. However, the refraction effect of the transparent display screen will cause errors in the 3D measured data. After analyzing the refraction light path in the transmissive display dual-screen system, this paper proposes a method of compensating the refraction error caused by the transparent display screen. To start with, we analyze the measurement principle of the transmissive display dual-screen system and the cause of the refraction error. Then, the refraction error introduced by the transparent display screen is compensated through phase in the parameter calibration process. Finally, the proposed method of refraction error compensation is verified on the developed measurement system. The experimental results show that the proposed method eliminates the error caused by the refraction effect and improves the measurement accuracy of 3D mirror object shape.

With the rapid development of the optical aspheric surface industry, it has become a trend to produce aspheric lens products with a surface shape accuracy better than 0.1 μm. In the surface shape detection of the aspheric lens, due to the existence of mechanical system error, the coordinates of the detected workpiece have a deviation of 6 degrees of freedom, which will directly affect the measurement accuracy of the aspheric surface. Therefore, we need to develop an error correction algorithm with an uncertainty of only tens of nanometers for the detection system to ensure that the measurement results are closer to reality. In view of this, this paper uses data simulation to superimpose the position error and the surface shape error on the ideal aspheric surface to obtain the original three-dimensional (3D) data of the aspheric surface, and then use the revised Levenberg-Marquardt global optimization algorithm to compare the obtained original 3D data with the standard equation of aspheric surface. The principle of minimum root mean square error is used to successfully separate and correct the position error of the aspheric surface. Finally, for four glass aspheric lenses of different specifications and models, through comparing the experimental results and measurement results of the commercial aspheric profiler UA3P, a high matching result is obtained. The difference in peak-valley values is less than 5 nm, and the difference in RMS is about 0.1 nm, which verify the accuracy and robustness of the algorithm.

The Gray-code assisted phase-shifting technique can achieve three-dimensional (3D) shape measurement with strong robustness and anti-noise ability. To solve the order edge error caused by the uneven surface reflectivity of the measured object, noise, object motion, and other factors, a dynamic 3D shape measurement method based on misaligned Gray code is proposed. The traditional Gray-code patterns are moved in advance by half fringe period before projection to obtain misaligned Gray-code patterns, then the traditional Gray-code decoding method is used to decode the binarized misaligned Gray-code patterns to acquire a decoding result that is completely staggered from the wrapped phase. By correcting the decoding result, the obtained correct phase order can be used to assist the wrapped phase to be successfully unwrapped. Meanwhile, a virtual phase plane is introduced to further expand the number of projected fringe periods and ultimately to improve the measurement accuracy. The experimental results show that the proposed method can perform 3D measurement by coding projection fringes with 2N+1 periods when N-frame Gray-code patterns are used, which can avoid the order edge error without any additional patterns and effectively improve the measurement accuracy. The 3D reconstructed results in complex dynamic scenes prove that the proposed method can achieve high-precision, high-efficiency, and high-speed 3D shape measurement at a rate of 2381 frames/s.

Metrological technique for traceability of an absolute radiometer to a cryogenic radiometer is studied. With laser as the light source, a calibration experiment is implemented in the radiation power mode in which the light spot does not fully cover the receiving plane of the absolute radiometer. The trap detector traceable to the cryogenic radiometer is used as the etalon to calibrate the laser, and the value is transferred to the absolute radiometer by substitution. The conversion from laser power to irradiance measured by the absolute radiometer is achieved by calibrating the aperture area of the absolute radiometer. The calibration uncertainty of the absolute radiometer used in the experiment is evaluated in detail by analyzing the calibration of the trap detector, the spatial response uniformity at different positions of the conical cavity in the absolute radiometer, and the wavelength selectivity of the cavity. The calibration uncertainty obtained is 0.86% (coverage factor k=2).

In the process of target push-broom imaging by a temporally and spatially modulated spatial heterodyne interference imaging spectrometer (TS-SHIS), the push-broom error and positioning error of the pointing mirror and the satellite platform vibration can deviate the actual imaging position (x',y') of a target from its ideal position (x,y). This results in spectral mixing between adjacent targets, affecting the interference data reconstruction and reducing the accuracy of recovery spectra. In light of the mechanism of TS-SHIS, this paper discussed the linear mixing of target spectra caused by motion errors and the influence of surface reflectance difference on the accuracy of recovery spectra. On this basis, the interference function of mixed targets was established with the mixing ratio of adjacent targets and the surface reflectance difference as variables. Further, we analyzed the surface reflectance differences of different spatial resolutions in China based on MODIS satellite payload data. Taking the relative spectral quadratic error as an evaluation function, we explored the effects of attitude parameters of a typical high-orbit platform on the accuracy of target recovery spectra with different spatial resolutions. This research provides a technical basis for the next generation of high-orbit greenhouse gas detection technology with high spatial and temporal resolutions.

In this paper, a silicon-based Mach-Zehnder interferometer (MZI) refractive index sensor working in the near infrared band is designed. Theoretical and simulation analysis show that the dispersion turning characteristics of the output interference spectrum can be regulated by changing the structural parameters of MZI. After optimization, the wavelength corresponding to the dispersion turning point (DTP) can be adjusted to the near-infrared band (1550 nm). By changing the ambient refractive index (SRI) around the MZI, the refractive index sensitivity can reach 37500 nm/RIU. Since the interference fringes on both sides of DTP have opposite characteristics to the refractive index response of the outside world, taking the relative drift of the interference trough as the detection object can improve the sensitivity by two times, the value is 75000 nm/RIU. Different from conventional DTP sensor based on grating and waveguide coupling structure, the two interference modes in the designed DTP structure are unrelated and can be adjusted independently, and the dispersion transition wavelength can be adjusted flexibly according to the needs.

An Er,Yb∶glass slab amplifier pumped by laser diode (LD) array is designed in this paper, which adopts a multi-bounce structure to improve extraction efficiency. It is expected to achieve the laser output with greater energy in the 1.5 μm band, and the laser amplification gain can reach 35.29. Based on the steady-state heat conduction theory, the thermal effect of the Er,Yb∶glass slab amplifier is analyzed and the thermo-mechanical coupling model is established. The thermodynamic characteristics of the slab medium at different parameters are compared by the finite element method. The results indicate that the thermal effect can be effectively alleviated by increasing the width-thickness ratio of the slab and reducing the power density of the pump light. Based on the analysis, a method for wavefront distortion compensation is proposed.

The lengths of the ridge waveguide (RW) region and the tapered gain region of a 1060 nm tapered laser are optimized for better output performance of such lasers. When the total length of the cavity is kept at 3 mm, the length of the ridge RW region is set to 500, 750, and 1000 μm. When the output power is 2 W, the required input currents, slope efficiencies of power-current curves, electro-optical conversion efficiencies, output spectra, and far-field characteristics of the three lasers are compared. The results show that the output performance of the 1060 nm tapered laser is best when the length of the RW region is 750 μm and that of the tapered gain region is 2250 μm. Under an output power of 2 W, the required input current is 3.95 A, the slope efficiency is 0.61 W/A, and the conversion efficiency is 33.9%,the width (full wave at half maximum) of the spectrum is 0.3 nm, the far field is approximately Gaussian distribution, and the horizontal divergence angle is about 14° at energy of 95%.

In order to carry out the experimental study of laser plasma instability (LPI) on the laser device cluster platform with an output energy of 100kJ, a scattered light diagnosis system based on cluster configuration is built. The diagnosis system uses the diffuse reflector as the main light blocking, reflection, and sampling element, the imaging method is used to image the scattered light to the recording components such as iCCD (intensifier Charge Coupled Device) camera, and the sampling measurement method is used to obtain the spatial distribution, energy, spectrum, and time waveform of the scattered light. In the cluster physics experiment, the physical data obtained by the system are in good agreement with the results obtained by the physical simulation program. It shows that the scattering mechanism is mainly subbeam mechanism under the current conditions, and its action process mainly concentrates on the early stage before the plasma empties.

A fibre laser oscillator is constructed using the bidirectional-pumping structure and a 25/400 μm (the core diameter is 25 μm and the cladding diameter is 400 μm). The gain medium is a large-mode-area double-cladding ytterbium-doped fibre, and a 915-nm semiconductor laser is utilised as the pump source. The suppression of fibre-stimulated Raman scattering and dynamic mode instability is accomplished via fibre selection, an appropriate ratio of forwarding and backward pump power and mode control. The fibre laser oscillator produced a maximum output power of 5.08 kW at a pump power of 7.5 kW, with a light-light conversion efficiency of 68%, and the suppression ratio of stimulated Raman scattering is 37 dB. The time-domain properties remained constant, with no evidence of dynamic mode instability. The beam quality measurement results of output laser in the X and Y directions at maximum power are 2.483 and 2.514, respectively. The far-field light spot had a ring shape, and the light intensity ratio between the ring area and the central area is 1.6. The fibre laser oscillator worked continuously for 1 h at maximum output power without any abnormality, and the temperature of the fibre optic components in all parts is within the acceptable range.

Gas laser based on hollow-core fiber (HCF) is an effective means to realize mid-infrared laser output. Generally, according to the transition selection rule, one pump absorption line corresponds to two lasing transition lines. A single-pass HCF HBr laser with a 4.3 μm single spectral line is realized by means of air pressure control. Using the self-developed 1958 nm continuous wave high-power narrow linewidth thulium-doped fiber amplifier as the pump source, a 5-meter-long anti-resonant HCF filled with low-pressure HBr gas is pumped. The laser output with 4.3 μm single spectral line of isotope H 79Br and H 81Br is realized respectively through air pressure control, the maximum laser power is 350 mW, and the total optical-optical conversion efficiency is about 8%. The output laser spot is measured by the self-built optical fiber scanning device, and the result shows that it is a fundamental mode.

350 nm polystyrene microspheres (PSs) are prepared on sapphire substrates as masks by nanosphere lithography technique, and then ZnO thin films are grown on PS/Al2O3 and Al2O3 substrates by reactive radio frequency magnetron sputtering method, respectively. X-ray diffraction analysis, scanning electron microscope observation, and photoluminescence (PL) test are used to measure two kinds of samples after annealing; the PS mask is removed from the Al2O3 substrate. The results show that the grains of the ZnO thin film grown on the PS/Al2O3 (sample 1) are obviously worm-like; the grains of the ZnO thin film directly grown on the Al2O3 substrate (sample 2) show incomplete hexagonal prism shape. Although the crystallization of sample 2 is better than that of sample 1, the intensity of near band edge photoluminescence peak of sample 1 around 362 nm is 43 times stronger than that of sample 2.

According to the task requirements on a light space remote-sensing camera of Jilin-1 satellite, a high-stability secondary mirror supporting structure was designed. For this purpose, integrated molding of the thin-walled cylinder and truss rod made of carbon fiber reinforced polymer composites was adopted as the design idea. And topology optimization, size optimization, and layer optimization were employed to design a secondary mirror supporting structure with high stability. The results of engineering analysis and tests show that the integrated carbon fiber secondary mirror supporting structure has favorable structural stability, with a mass of 1.3 kg. The on-orbit imaging performance of the space camera is great, which further verifies the reliability of the proposed supporting structure and the correctness of the design method.

A novel low-cost trough concentrator based on the same parabolic mirror unit rotating array is proposed. The optical analysis model of the concentrator is established by ray tracing method, and the influence of key parameters such as mirror focal length (f), mirror width, position of plane receiver, radius of rotating array (R1) and number of rotating arraies (N) on its concentrating performance is studied in detail, which provides an important basis for the design and application of this concentrator. The results show that the novel trough concentrator can concentrate solar energy well, and it is different from the traditional parabolic trough concentrator, which concentrates parallel light at a certain point, but concentrates light “dispersedly”, and it has the potential to realize uniform focusing energy flux distribution on the plane receiver. The reasonable receiving position of the focusing spot will change with the change of radius of the rotating array. Generally, it is appropriate for the receiver to be located at half of the radius of the rotating array, but to obtain the minimum focusing spot, it needs to be moved down by 150--200 mm. The width of focusing spot increases exponentially with the mirror number, especially when the mirror width is large and the mirror rotating array radius is small. The larger the radius of rotating array or the smaller the mirror width is, the more concentrated the focusing energy flux distribution is and the larger the peak concentrator ratio is (50 in the calculated example). In this case, the focusing energy flux basically shows the characteristic of Gaussian distribution. In addition, the installation height of the receiver can be reduced and the energy flux uniformity can be improved by using a smaller radius of rotating array. In an calculated example, when f=8000 mm, R1=4000 mm, N=5 and the receiver is located at 1830 mm, the energy distribution of focusing spot is very uniform and the concentration ratio in most areas is stable at 7.3, the concentrator is very suitable for concentrated photovoltaic/photothermal applications.

Challenges exist in current flexible waveguide devices, such as the fabrication difficulties, mechanical flexibility limitation, and poor reliability. Based on the neutral-plane theory, flexible multimode polymer waveguides with a sandwich structure are designed and fabricated on the polyimide (PI) substrate. The flexible waveguide is endowed with excellent structural reliability and mechanical flexibility by constructing multiple neutral surfaces. The resultant flexible multimode optical polymer waveguides exhibit lower propagation loss (0.16 dB/cm at 850 nm) and lower inter-channel crosstalk (<-40 dB). Excellent mechanical bending property of the flexible waveguides (bending radius less than 3 mm) is also achieved by using micron-mechanical designs to minimize strain exerted on the waveguide core layer during mechanical deformation process. The transmission loss is not significantly increased when the bending radius is 1 mm and the bending is repeated 1000 times. Besides, the reliability test results reveal that the optimized flexible waveguide has excellent thermal stability, aging resistance, and machinability, for which, the resultant flexible waveguides show no performance degradation after humidity cycling, temperature cycling,and lead-free reflow soldering tests. Hence, this work provides theoretical and technical guidance for the practical mass-production of high quality flexible polymer waveguides with excellent mechanical flexibility and environmental reliability.

A simple chemical substitution reaction method is used to grow needle-like gold nanostructures on nickel foam substrates, which are used as surface-enhanced Raman scattering (SERS) substrates to study the effect of substitution time on the properties of SERS substrates. COMSOL Multiphysics simulation software is used to simulate the electromagnetic enhancement of gold nanoparticles with the heights of 100,150,175,200 nm, respectively, and the maximum electric field intensity is 20.112, 29.060, 24.766, 21.382 V/m, respectively. The enhanced factors are 1.64×10 5, 7.13×10 5, 3.76×10 5, and 2.09×10 5, respectively. Using rhodamine 6G (R6G) solution as probe molecule, Raman characterization, detection limit test, and Raman mapping test are carried out on the nickel foam gold-plated substrate at different replacement times. The test results show that the substrate with displacement time of 10 min has the best enhancement effect, and the detection concentration of R6G molecule can reach 10 -8 mol·L -1, RSD (Relative Standard Deviation) values at the characteristic peaks of Raman shift of 613, 774, and 1364 cm -1 are 11.3%, 10.9%, and 11.9%, respectively. It shows that the substrate has good uniformity, the enhancement factor is 1.04×10 5.

In order to realize the requirements of small structure and high sensitivity of optical refractive index sensor, a single baffle metal-insulator-metal (MIM) waveguide coupled with cloud like cavity is proposed according to the transmission characteristics of surface plasmons. This structure refers to the concept of "cavity within a cavity". Under the action of near-field coupling, the wide continuous state formed by a cloud like cavity and the narrow discrete state formed by a metal baffle can be eliminated by interference, resulting in three Fano resonances with different modes. Combined with the coupling mode theory, the generation mechanism of triple Fano resonance is analyzed, and the finite element analysis is used to simulate the structure, and the influence of different structural parameters on the refractive index sensor characteristics and quality factors is quantitatively analyzed. The results show that the sensitivity of the three resonant modes are 600, 800 and 1083 nm/RIU, and the high quality factors are 5.08×10 4, 3.56×10 5, and 1.17×10 3, respectively.

In this paper, a new theoretical model of Laguerre-Gaussian power-exponent-phase-vortex beams (PEPVBs) was established, and the theoretical propagation model of the Laguerre-Gaussian PEPVB under paraxial approximation condition was established by using the generalized Collins formula. Then, the relationships among the transmission and focusing characteristics, radial order, topological charge, power index, and transmission distance of Laguerre-Gaussian PEPVBs in free space are simulated by using MATLAB. Research results show that the Laguerre-Gaussian PEPVB and its transmission characteristics are not only related to the power exponent and topological charge, but also related to the radial order of the Laguerre-Gaussian polynomial. And as the transmission distance increases, the beam energy rotates and gathers around the ring. This lays the groundwork for optically manipulating particles to make them move along curved paths and avoid obstacles, which has great significance to the theory and application of new light field control.

This paper takes two isomers of sugars [D-(+)-glucose and D-(-)-fructose] as the research object. Firstly, the terahertz time domain spectroscopy system was used to obtain the characteristic absorption spectra of the two isomers in the band of 0.4--1.9 THz. The two different absorption peaks at 1.43 THz and 1.64 THz can be used for qualitative identification. Secondly, in order to further explore the formation mechanism of absorption peaks, the density functional theory was used to optimize the cell structure and identify the vibration modes. Finally, the types, locations, and intensities of the weak intermolecular interactions between glucose and fructose cells were visualized by the reduced density gradient and independent gradient model. The research results show that the characteristic absorption peaks of the two substances in the terahertz band are mainly derived from the collective vibration mode caused by the hydrogen bond interaction between the functional groups of the two molecules. This study provides valuable experimental and theoretical references for the qualitative detection of the isomers of sugars and precise quantitative analysis, as well as the formation mechanism of terahertz absorption peaks of D-(+)-glucose and D-(-)-fructose.

Aiming at the identification of the characteristics of the discrete three-dimensional fluorescence spectra for the planktonic mixed algae community, the spiecies identification accuracy and concentration measurement accuracy of mixed data of five common phylum species of algae (Microcystis aeruginosa, Scenedesmus obliquus, Nitzschia sp., Peridinium umbonatum var.inaequale and Cryptomonas obovata.) are compared and analyzed by the plain convolutional neural network (PlainCNN) model and the text convolutional neural network (TextCNN) model. The results show that in the algae independent identification and concentration regression analysis, the average identification accuracy of the test set and the average mean square error of the results of the concentration output of the PlainCNN model are 90% and 0.052 respectively, which are better than that of TextCNN model. In order to realize species identification and concentration analysis of mixed algae at the same time, a multi-task convolutional neural network, i.e., PlainCNN-MT model, is proposed based on the PlainCNN model. The average accuracy of the model for the species identification of mixed algae is increased to 95%, and the average mean square error of the results of the concentration output is reduced to 0.039, indicating that the multi-task convolutional neural network has more advantages in the identification and quantitative analysis of planktonic algae community.

In order to test the performances of CIE recommended color matching functions, including CIE1931, CIE1964, and CIE2006, the visual color differences from young and aged observers in the previous study based on paired-comparison experiments are used to test the performances of CMFs. The results indicate that CIE2006 (22, 4°) and CIE1931 2° are recommended for young and aged observers with the minimum STRESS values, with the most consistent of the calculated color difference ΔE00 and the visual color difference ΔV of 56 young observers and 40 old observers, respectively. Further, we selected five neutral target colors from RAL K5 color chart with the L*10 values ranging from 34.4--71.6, and 16 metamerism samples were prepared by the Epson inkjet printer around each target color sample. The target and compared samples were metamerism sample pairs. 26 young observers were organized to carry out the color difference experiment of the 80 sample pairs with the gray scale method. The results indicate that the computed color differences ΔE00 from CIE 2006(22,2°) CMFs are accorded with the visual color difference ΔV with the minimum STRESS values, with the observation field of 8.17°×16.26°. The existing CIE2006 CMFs are needed to improve in the calculation of large field of view in consideration of the color difference of metamerism reflected samples.

Color constancy is an important prerequisite for computer vision tasks such as object detection, three-dimensional object reconstruction, and automatic driving. In order to make full use of the feature information of different scales in the image to estimate the light source, a progressive multi-scale feature cascade fusion color constancy algorithm is proposed. The feature information in the image is extracted from different scales by three convolution network branches to fuse and get more abundant feature information. By cascading the shallow edge information and the deep fine-grained feature information in the image, the accuracy of the color constancy algorithm is improved. The progressive network structure improves the robustness of the algorithm for the light source estimation in extreme scenes by weighted cumulative angle error loss function. Experimental results on the reprocessed ColorChecker and NUS-8 datasets show that the proposed algorithm outperforms the current color constancy algorithm in terms of various evaluation indexes, and can be applied to other computer vision tasks requiring color constancy preprocessing.

Since the calculation of correlated color temperature and color deviation of light source has always been the focus of researchers, an efficient hybrid method based on triangle method, parabolic method, and third-order polynomial method for calculating correlated color temperature and color deviation of light source is proposed. The accuracy of the proposed method is tested and compared with that of Ohno and Robertson methods by using 90005 data sampled from 18001 isotemperature lines with colour temperature between 2000 K and 20000 K at 1 K step, and color deviation between -0.030 and 0.030 at 0.015 step. The test results show that the proposed method is better than Ohno and Robertson methods with maximum absolute difference of correlated color temperature being less than 0.3858 K and maximum absolute difference of color deviation being less than 3.33×10 -6 respectively, so it can be directly used in LED spectrum optimization and design.