ConclusionsBased on the vector scattering theory and with bidirectional reflection distribution function and total scattering loss as evaluation indexes, the influence of interface electric field intensity on light scattering characteristics of multilayer highly reflective thin films is analyzed and theoretically and experimentally verified. The reflectivity at the center wavelength of 632.8 nm is required to be larger than 99%. Two kinds of multilayer dielectric high-reflectivity films are designed by using Ta2O5 and SiO2 films on the premise of meeting the spectral design requirements. The surface reflectivity and the distribution of electric field intensity in the film system are analyzed, and a film system with an optimized interface electric field intensity is proposed. Finally, the effectiveness of the proposed method for reducing scattering caused by interface roughness of multilayer dielectric films by adjusting the interface electric field intensity of multilayer dielectric films is verified from the theoretical calculation and experiments.

ConclusionsSiAlON is chosen to replace SiO2, a commonly used low-refractive index material in the visible light band. Its refractive index at 550 nm is about 1.501, which is similar to that of SiO2. But its hardness can reach 1500 HV. In contrast, the hardness of SiO2 is 800 HV. Although the refractive index is similar, the hardness of SiAlON far exceeds that of SiO2. In the visible light waveband, the super-hard anti-reflection film made of SiAlON and Si3N4 has an average hardness of 1773.9 HV, and the average reflectivity is about 0.489% after the film system is optimized, which improves the film hardness while ensuring the anti-reflection effect. The film has passed a variety of environmental tests, which not only provides better protection for the display screens of electronic products, but also has important significance for other optical components that have higher requirements in terms of low reflection and high hardness.

ConclusionsThe high-quality ZnO films are deposited on glass and silicon substrates using a laser deposition process in different burst modes, with the number of subpulses in each burst increasing from 1 to 4. The effects of different burst modes of picosecond lasers on the film thickness, roughness, surface topography, crystal structure, optical properties, and electrical properties of ZnO films are investigated. When the pulse burst mode is set to 4, the film surface has less roughness, smaller particle size, higher transmittance, better crystalline quality, and lower resistivity when compared with other burst modes. This is extremely important for relevant optical applications to the production of ZnO thin film.

ConclusionsIn summary, this paper proposes an accurate and fast design method to design a narrow bandpass optical transparent FSS. Two structural parameters are optimized under the design goals by this method and are verified to be close to the design goals by full-wave simulation, with the losses of transmission peaks less than 1.5 dB at the desired frequency, the out-of-band suppression larger than 20 dB, the quality factors of transmission peaks larger than 26, the visible light transmittance acceptable, and the structure not sensitive to polarization angles. In addition to optimizing the structural parameters of the bandpass optical transparent FSS at the desired transmission frequency point, this design method can also be used to optimize design goals of different optical transmittances and dielectric materials, or a multi-layer FSS that consists of media and metal grids. Therefore, this method can effectively optimize the structural parameters of the FSS composed of dielectric and grid structures under desired design goals, greatly reduces the design time of the metal grid type FSS, and provides convenience for the design of the FSS.

ConclusionsThis paper presents a robot pose estimation algorithm that is based on the fusion of dynamic feature elimination images and point clouds. The method of deep learning is used to extract the candidate frame of the target object from an image and point cloud, which is then used for data processing and feature optimization. It completely avoids the error function abnormality caused by incorrect matching of dynamic features and eliminates its effect on the pose estimation. Simultaneously, this paper performs a dynamic weighted fusion of the pose based on the number of feature points. Finally, this paper uses the public KITTI data set and the experimental data collected by the experimental platform construct-in dynamic scenarios to compare the pose estimation accuracy of the three mainstream algorithms of BA, LOAM, and ORBSLAM2. Experiments show that removing dynamic features improves the accuracy of pose estimation to varying degrees. The posture result after fusion is more stable. Furthermore, the sequential processing logic ensures that the system is unaffected by the running time in the offline state to correctly process each frame of data.

ConclusionsIn our experiment, the preinscribing method replaces the traditional preload monitoring method. The other error is reduced by directly monitoring the wavelength change; the FBG inscribing wavelength precise controlling is realized. We inscribed six FBGs with different wavelengths; the actual inscribed value of the center wavelength is in good agreement with the target value. The mean error of the FBG center wavelength is 0.007 nm and the standard deviation of error is 0.029 nm. Thus, our method proves to be simple, stable, and reliable, and it can effectively improve FBG center wavelength writing accuracy.

ConclusionsThe InGaAsP/InP multiple-quantum-well coupled-circular micro-cavity laser with a radius of 15 μm is measured by the constant current aging test at 100 mA for 1400 h. The variations of laser output power and threshold current during the test are consistent with those of a semiconductor laser under the gradual degradation mode except for three abnormal variations caused by the change of mode or ambient temperature, that is, the lifetime of the laser can be evaluated according to the output power variation. The laser output power is reduced by 50% after 1200 h, that is, the lifetime of the laser is about 1200 h at 100 mA.

ConclusionsIn this paper, the free-running characteristics of the 633 nm internal-mirror He-Ne laser tube at the ambient temperature of -20-40 ℃ are studied. The experimental results show that when the laser tube reaches the thermal equilibrium at different ambient temperatures, the difference between the laser tube temperature and the ambient temperature is fixed, the expansion rate is also the same, and the voltage difference of the double longitudinal mode changes for the same period. According to these characteristics, the preheating and frequency stabilization control scheme of the laser system is designed, and the frequency stabilization of the 633 nm internal-mirror He-Ne laser is realized. When the room temperature is about 24 ℃, the beat frequency results of the locked thermally stabilized laser and the high-precision iodine stabilized laser show that the relative standard uncertainty of frequency within 3 h is u=6.4×10-9. When the sampling time τ=1 s, the corresponding Allen variance is 7.0×10-11. When 0.1 s≤τ≤2000 s, the Allan variance is better than 4.3×10-10, and the frequency reproducibility within 3 months is better than 4.6×10-9. This paper also studies the frequency drift law of the output laser after locking at the ambient temperature of -20-40 ℃. The experimental results show that the temperature of the laser tube wall changes linearly with the ambient temperature after frequency stabilization. At the same time, the drift of the laser output frequency with the ambient temperature after frequency stabilization is about 293 kHz/℃, which is consistent with the drift value of 268 kHz/℃ calculated by the pressure estimation model. In this regard, when the laser is working in a large temperature range (such as -20-40 ℃), interpolation calibration can be used to obtain a more accurate reference output frequency.

ConclusionsThis paper reports the CTFBG with the ability to support the highest power laser at home and abroad. The CTFBG on 25 μm/400 μm fiber supports the more than 4 kW laser power with an insertion loss of less than 0.3 dB and a high thermal handling capacity (~1.72 ℃/kW). It is of great significance to promote the development of domestic high-power CTFBGs and expand their applications in high power fiber laser systems.

ConclusionsIn this paper, a method for detecting the internal stress of a steel plate based on laser ultrasonic guided waves is proposed. The experimental results show that a pulsed laser can excite broadband laser ultrasonic guided waves in the silicon steel plate, and the A0 mode is the main mode. The phase velocity of the laser ultrasonic guided wave increases with the increase of tensile force, while the group velocity decreases with the increase of tensile force. There is an obvious linear relationship between tensile stress and the time difference of head wave advance and wave packet delay of the laser ultrasonic guided wave signal. The laser ultrasonic guided wave testing method can be used to realize the non-destructive, non-contact, and high-precision detection of internal stress of a strip steel, and this method may become a new method for the on-line stress detection of strip steels.

ConclusionsAiming at the problem of laser noncoplanar error encountered in the full section measurement of rail profile, a laser noncoplanar error correction model based on projection transformation is proposed, the principle and steps of error correction are described in detail, and the effectiveness and accuracy of the proposed method are verified by experiments. The proposed method reduces the rail profile measurement error caused by noncoplanar laser installation to less than 0.10 mm. This method does not require the laser planes on the left and right sides of the rail to be perfectly coplanar, but only that they be roughly aligned. It not only ensures rail profile measurement accuracy, but also greatly reduces the requirements for component processing accuracy and on-site installation environment, and avoids the time-consuming and labor-intensive laser plane fine adjustment process on site.

ConclusionsIn this study, the numerical simulation method is used to systematically analyze the changes of the effective diffraction area of the next-generation single lunar corner reflector under different laser beam incident conditions. The influence of different lunar corner retroreflector orientations on ground observations is comprehensively discussed. The Levenberg-Marquardt method is used to optimize the corner retroreflector orientations in three typical regions by simulating the real observation time. The results show that the moon’s apparent libration is the main influencing factor affecting the effective diffraction area. This effect can only be reduced by optimizing the orientation, and there is no way to eliminate it. Meanwhile, the observation efficiency of low-latitude laser lunar stations is significantly higher than that of high-latitude stations. In addition, China is located in the eastern part of Asia, forming an excellent complementary effect with the stations in European countries and the United States. The results suggest that we should fully utilize the favorable conditions at the two low-latitude stations, the 1.2 m laser lunar ranging station of Yunnan Observatories, Chinese Academy of Sciences and the Zhuhai Tianqin laser lunar ranging station, to make significant contributions in future lunar exploration and laser ranging experiments.

ConclusionsBased on the traditional laser echo theory, the multitarget laser echo power equation is deduced and simulated and the effects of target laser irradiation area and incident angle on the waveform echo are examined. A multitarget detection experimental platform is built to validate the accuracy of the echo equation, and the effect of circuit overshoot on multiwaveform research is verified through experiments using various receiving circuits, which provide a calculation model for full-waveform decomposition and inversion. Following are the conclusions that can be drawn from the simulation and experiment. The target irradiation area is directly proportional and the laser incidence angle is inversely proportional to the echo peak. For the receiving circuit with voltage overshoot, the experimental results show that when the distance between multiple targets is large, the abscissa difference of the waveform peak in the echo waveform is greater than that of the single waveform pulse width and the average experimental relative error is less than 5%. When the distance between multiple targets is less, the abscissa difference of the waveform peak in the echo waveform is less than that of the single waveform pulse width, the experimental relative error increases, and the average value is more than 10%. After using the new receiving circuit to eliminate the voltage overshoot, the experimental relative error is reduced and the average value is less than 6%. It is demonstrated that improving the receiving circuit’s overshoot or fitting overshoot can improve the accuracy of full-waveform echo decomposition.

ConclusionsOwing to the low-loss characteristics of the all-dielectric materials, this paper proposes a metasurface with a silicon gap disk structure as a platform for microfluidic sensing and detection. The structure can be directly excited by incident light to produce a broad-spectrum electric dipole bright mode in a symmetrical state. When a rectangular nano-notch is introduced into the structure, the dark mode is excited, resulting in the formation of two new Fano resonances. The hybrid resonance is produced by the coupling of the electric quadrupole mode and electric dipole, as well as the magnetic Fano resonance is dominated by the magnetic dipole. The transmission spectrum characteristics are examined using the 3D FDTD method, and the influence of various structural parameters is investigated. It is observed that the structure can simultaneously achieve independent and nonindependent parameter tunings. Furthermore, the effect of the analytes with varying thicknesses in the microfluidic device on sensing performance is investigated. By selecting the optimized structural parameters, the sensor has a maximum sensitivity of 400.36 nm/RIU and a maximum Q value of 1252.3. The proposed structure provides a theoretical reference for the design of biosensor detection devices.

ConclusionsIn this paper, two-dimensional periodic and Hilbert fractal superlattices were manufactured, and their Fraunhofer diffraction experiments were performed using lasers with wavelengths of 532 and 633 nm, respectively. The experimental results agree well with simulation calculations. Owing to the stronger order and complexity of the Hilbert fractal structure, the distribution of reciprocal vectors is rich in reciprocal space. Furthermore, the second harmonics at wavelengths of 543, 696, and 900 nm were achieved in the lithium niobite of the Hilbert fractal superlattice structure using theoretical calculations. Additionally, owing to small reciprocal vectors, the second harmonic with a wavelength of 632 nm was generated after linear combinations, thereby obtaining the effective output in the near-infrared and mid-infrared bands. Therefore, Hilbert fractal nonlinear photonic crystals with rich reciprocal vectors are expected to be used in multiband frequency conversion, optical parametric oscillator optimization, broadband pulsed white laser design, realization of multi-period terahertz pulses, and nonlinear photonic crystal light field modulation.

ConclusionsBased on the variable coefficient nonlinear Schr?dinger equation, this paper investigates the dynamic characteristics of the symmetric Airy pulses with an initial chirp under periodic dispersion modulation. The results show that the chirp parameter C and the main lobe position d determine the number and positions of focal points generated by the collision during the transmission of the chirped symmetric Airy pulses. Within the evolution distance of a dispersion cycle, when |C|d of the main lobe as the pulse trajectory does not reverse. When |C|=0.5, the trajectory of the pulse will be reversed once, and there will be two focal points in the evolution of the pulse. The main lobe position d can only affect the position of the focal point; it does not affect the number of focal points. Furthermore, when |C|>0.5, the trajectory of the pulse will be reversed twice, and there are at least two focal points. Moreover, the number of focal points can be increased to three at most four by adjusting the main lobe position d. Additionally, the truncation parameter does not affect the number and the position of the focal points. However, a larger truncation parameter will lose more energy under collision. When the Kerr nonlinear effect is considered, the transmission characteristics of the pulse are nearly unchanged under the small nonlinear effect. As the nonlinearity further increases, it causes soliton shedding. Stronger nonlinear effect can also lead to the generation of multiple solitons and the collision of solitons with side lobes. This periodic transmission process and focusing characteristics provide certain theoretical guidance for the research and the application of properties, such as the self-reconstruction of Airy pulses.

ConclusionsAn optimized double resonance system consisting of a silver grating and silver nanoparticles is achieved through analyzing the extinction spectra and the field enhancement simulated by the FDTD method. The redshift of resonance positions of the Ag grating provides a chance for it to match the resonance of the Ag nanoparticles. Regarding Ag nanoparticles with a diameter of 50 nm and a gap distance of 2 nm, 520 nm is determined as the optimized period for the Ag grating to obtain the strongest field enhancement under excitation wavelengths of 532, 633, and 785 nm. The ridge width of the grating has little effect on field enhancement for the hybrid structure, so 258 nm is chosen as the ridge width for the grating with a period of 520 nm. A 4 nm thick gold layer is added on the surface of the Ag grating in simulation to improve its chemical stability and the better field enhancement is shown. The proposed Ag-Au grating/Ag nanoparticles system can be potentially used in SERS researches because of its high sensitivity and chemical stability.

ConclusionsIn this paper, the influence of the number of spatial confinement walls on laser-induced Cu plasma spectra was studied in an atmospheric environment. The experiment discovered that the spectral intensity, SBR, and electron temperature of Cu plasma increased with increasing spatial confinement walls; when the confinement cavity was the cylindrical wall, the spectral intensity, SBR, and electron temperature of the plasma were the highest. The spatial confinement effect resulted from the shock wave reflected from the confinement cavity wall compressing the plasma plume. As the number of confinement walls increased, the energy of the shock wave used to confine the plasma continued to grow, and the coupling degree of the shock wave and plasma plume was also increasing, resulting in the continuous enhancement of the compression effect of the plasma. In conclusion, it can be seen that a sufficient number of spatial confinement walls can effectively increase the spectral intensity, SBR, and electron temperature, thereby improving spectral signal and sensitivity.

ConclusionsThe performance of astronomical ultraviolet gratings is optimised in groove parameters to achieve the best average efficiency under a variable incident angle and controlled polarisation sensitivity operating conditions. After a few turns of fabrication and evaluation, good grating performance is achieved. This will be a contribution to the application of sky spectrum surveys.

ConclusionsBased on the transmission terahertz time domain spectral system, a novel rotating optical delay line is designed. The rotating optical delay line contains 24 planar mirrors, which can change the optical path by rotating to produce a variable time delay. A mathematical model of the optical delay line is established, and the optical path simulation and the actual experimental verification under working conditions are carried out. Simulation and experimental results show that the delay time can reach 72 ps, the scanning frequency is 60 Hz, and the linearity calculated by the least square method can reach 99.96%. Using the finite element analysis software, the force and modal analysis of the mechanical structure of the delay line are carried out in the rotating state, which ensure the reliability and stability of the design in work. Compared with the linear delay line in the existing terahertz time domain system, this FRODL has a fast scanning speed and linear delay time. The FRODL is more suitable for fiber optical systems, which has great advantages of miniaturization and integration of the THZ-TDS system relative to linear optical delay lines.

ConclusionsIn this paper, the influences of both the PNT and CNT on the THz wave generation are studied by the PIC numerical simulation. It is found that both PNT and CNT can generate THz waves with a broad bandwidth at the behind of the target. It is found that the front-end conical opening nanowire target can significantly enhance terahertz wave generation, and the terahertz wave electric field is increased by three times compared with that of the ordinary nanowire target. The reason why the CNT can enhance THz waves is analyzed in detail. The main reason is that the front-end conical opening structure of the CNT can significantly reduce the reflection of lasers, and thus improve the energy coupling efficiency between the laser and plasma. This makes a much higher cut-off energy and a larger number of hot electrons generated behind the target, which makes it radiate strong THz wave behind the target. The above results may contribute to the development of terahertz wave generation via laser-plasma interaction.