Lasers and laser optics
2021, 50(S2): 20210296.
doi: 10.3788/IRLA20210296
Damage characteristics of triple-junction GaAs solar cells irradiated by nanosecond pulsed lasers and their effects on photoelectric conversion were studied. The experimental system was established including damage morphology, voltage-current characteristics, and electroluminescence. The gradual decline characteristics of the photovoltaic performance of the cell was analyzed from the material ablation morphology, electrical performance output, and internal damage. On the basis of analyzing the influences of laser energy density, the influence of laser irradiation regions, such as the grid line part and non-grid line part of the cell, was further analyzed. Nanosecond pulsed lasers can cause obvious damage to the cell due to its high peak power. The damage effect of the grid line part of the laser was stronger than that of the non-grid line part, mainly because the function of the grid line electrode was used to collect photo-generated carrier. When the laser radiation fused the cell grid lines, which was used to collect photogenerated carriers, the output power of the cell was reduced. The research conclusions are of great significance for improving the protection capability of the solar cells.
2021, 50(S2): 20200474.
doi: 10.3788/IRLA20200474
Selective laser sintering (SLS) technology is developing rapidly and has been highly technology maturation, which can build complex insulation structures. However, it is difficult for traditional injection molding process to make some insulating parts with complex structures. Therefore, SLS technology has significant advantages in the production of complex insulating structures. However, different process parameters have great influence on the properties of samples. The density and insulation properties of nylon 12 samples under different laser powers were studied. Different laser powers were selected and the density, breakdown strength, conductivity and permittivity were taken as experimental indexes to select the optimal laser power. The mechanism of thermal oxidation degradation of nylon 12 was analyzed which resulted in the properties deterioration of samples. The results show that the density and insulation properties of samples are improved, then stabilized and degraded in the range of laser power. The optimal laser power is 9 W, the scanning speed is 3000 mm/s and the scanning spacing is 0.1 mm. The density of samples is 1.0106 g/cm3, the DC breakdown strength is 81.57 kV/mm and the conductivity is 4×10−13 S/cm.
2021, 50(S2): 20210277.
doi: 10.3788/IRLA20210277
In order to study the laser ablation propulsion performance of different metal materials, an Nd:YAG laser with a wavelength of 1064 nm and a pulse width of 8 ns was used to ablate seven common metal materials: Al, Fe, Ni, Cu, Y, Ag and Au in the atmosphere. Propulsion performance parameters such as ablation mass, impulse, impulse coupling coefficient, specific impulse and energy conversion efficiency were measured, and the influence law of laser power density on propulsion performance was obtained. The experimental results show that under the same laser power density, the ablation amount of Fe is the largest, the ablation amount of Y is the smallest. The impulse of Al, Au and Cu is larger, while that of Ag is the least. Au's impulse coupling coefficient and specific impulse mean value are the largest among the seven metals, reaching the maximum value of 40.7 μN/W and 500 s when the laser power density is \begin{document}$1.72 \times {10^{10}}\;{\rm{W}}/{\rm{c}}{{\rm{m}}^2}$\end{document} ![]()
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\begin{document}${{2}}{{.98}} \times {10^{10}}\;{\rm{W}}/{\rm{c}}{{\rm{m}}^2}$\end{document} ![]()
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2021, 50(S2): 20200099.
doi: 10.3788/IRLA20200099
Aiming at the problems of poor working environment, low operating efficiency, large operating error and high cost of the stacker and retractor in the enclosed stockyard, a set of intelligent control system for stacker and retractor was designed. The system was based on LiDAR technology, through the scanner to obtain stock pile surface point cloud data, the positioning system with the combination of scanner calibration was used to completethe real-time matching between the positioning sensor feedback profile data and scan data, realize the point cloud dataprocessing and 3D reconstruction of stock. Through image processing technology, the operation path was forecasted advance to guide the stacker and retractor to complete automatic operation in a enclosed stockyard. Experiment shows that the control system improves the work efficiency and reduces the operation cost.
2021, 50(S2): 20210323.
doi: 10.3788/IRLA20210323
Aiming at the problem that the evaluation of laser jamming effect is influenced by subjective experience and difficult to evaluate quantitatively, a laser jamming effect evaluation method based on deep learning was proposed. Firstly, the overall introduction of the YOLOV5 algorithm was given. Secondly, 3 020 laser jamming image from different angles and distances were produced. Then, the labeled data sets were trained to obtain the laser jamming effect evaluation model. Finally, the model was trained 300 times under the network models of YOLOV5x, YOLOV5l, YOLOV5m and YOLOV5s respectively. The experimental results show that the trained model can be used to evaluate the effect of laser interference image. The model could not only automatically label the laser interference area and evaluate the interference effect level, but also integrate the traditional strategy. It could calculate the area of the labeled area in the whole image as an auxiliary decision. The percentage of laser jamming area was automatically marked. The recognition accuracy was more than 80%, which is of great significance to the evaluation of laser jamming effect.
2021, 50(S2): 20200415.
doi: 10.3788/IRLA20200415
In order to study the characteristics of temperature field and stress field of fused silica irradiated by millisecond-nanosecond combined pulse laser, based on the theory of heat conduction and elastic-plastic mechanics, two dimensional axisymmetric geometric model was established, the numerical simulation software was used to analyze the process that fused silica irradiated by millisecond-nanosecond combined pulse laser. The temporal and spatial distribution and variation of the transient temperature field and stress field on the surface and inside of fused silica were obtained. The result shows, in the combined pulse laser, the millisecond pulse width is 1 ms, the energy is 120 J, the nanosecond laser pulse width is 10 ns, the energy is 80 mJ, Δt=1.0 ms, the best time delay for the temperature of fused silica irradiated by millisecond-nanosecond combined pulse laser, according to the different energy ratio of millisecond and nanosecond, the thermal effect of millisecond pulse laser on fused quartz and the stress effect of nanosecond pulse laser on fused quartz are obtained.
2021, 50(S2): 20210236.
doi: 10.3788/IRLA20210236
Using the energy transmitting fiber to replace the optical guide arm can greatly improve the flexibility of the medical handle, reduce the complexity of the system and improve the efficiency of laser transmission. A 2.79 μm Er, Cr: YSGG laser and its fiber coupling system were designed and developed. The influence of the output mirror of the laser resonator on the parameters of the output Gaussian beam was analyzed. A meniscus type lens was designed as the output mirror of the laser resonator to reduce the divergence angle of the laser beam, and a suitable coupling single lens was selected to meet the coupling conditions of the ZBLAN glass fiber with a numerical aperture of 0.29 and a core diameter of 400 μm. The experimental results show that when the meniscus type lens is used as the laser output mirror and the focal length of the coupling lens is 20 mm, the coupling efficiency of the laser transmission can reach up to 83%, and the maximum transmission power is 6 W, which meets the clinical application requirements of the laser medical instrument.
2021, 50(S2): 20210297.
doi: 10.3788/IRLA20210297
The ablation quality under laser micro-scale ablation is an important physical quantity for evaluating performance parameters such as specific impulse in the laser micro-propulsion system. Based on the ablation pit image obtained by the scanning electron microscope, a micro-scale ablation pit shape three-dimensional model reconstruction algorithm was established based on the gray-scale surface reconstruction method; In view of the effect of image noise, the image was segmented and smoothed, which effectively solved the effect of quantization error and grayscale blur on the reconstructed shape, and realizeing the ablation pit volume estimation. The results show that the proposed method can quickly and effectively reconstruct the three-dimensional shape of ablation pits under laser micro-scale ablation, and then calculate the ablation quality.
2021, 50(S2): 20210539.
doi: 10.3788/IRLA20210539
GF-7 satellite is equipped with the first laser earth observation altimeter with full waveform recording ability in China, which can obtain a wide range of high-precision three-dimensional coordinates, and its positioning accuracy is highly dependent on the measurement accuracy of laser pointing angle. According to the characteristics of data, a centroid extraction algorithm of ellipse fitting spot with threshold constraint was proposed, and a long-period pointing angle stability monitoring system was established. Firstly, the threshold method was used to determine the edge of the laser spot contour. Secondly, the influence of porosity and noise was eliminated through corrosion operation. Then, the shape of the laser spot was further constrained by ellipse fitting, and the characteristic parameters of the laser spot were preserved. Finally, the centroid coordinates were extracted by using the gray gravity center method. The experimental results show that the centroid position of the spot changes within 1.4 pixel, and the corresponding pointing angle changes within 0.434″ per month, which is relatively stable. The related algorithms and conclusions in this paper have certain reference significance for the development of laser altimetry satellites and the monitoring of pointing stability in China.
2021, 50(S2): 20210264.
doi: 10.3788/IRLA20210264
The migration mechanism of the target material in the millisecond laser drilling process directly affects the morphology of the hole. Therefore, the study of it was of great significance for the optimization of laser parameters. The migration of the material includes the migration of off-target gasification products, sputtered molten materials and non-off-target molten materials, and the molten materials was re-solidified to form the recast layer. For the off-target material, the high-speed camera was used to observe the movement law; For the recast layer, the metallurgical microscope was used to observe its morphology; Finally, the mass loss was measured with an analytical balance. The results show that the phase explosion threshold of aluminum alloy is 1 047.24 J/cm2. When the energy density is below the phase explosion threshold, the off-target material mainly migrates in the form of vaporization, and form circumferential and radial cracks. When the energy density is above the phase explosion threshold, the molten material is washed out of the ablation hole, and there is almost no recast layer inside the hole. The quality of gasification loss is very small. The mass loss mainly comes from the melt splash driven by the phase explosion. The phase explosion increases the single-pulse ablation quality by 10.7 times. Both the phase explosion and the decrease of laser intensity cause the vaporization rate of the target material to decrease.
2021, 50(S2): 20200198.
doi: 10.3788/IRLA20200198
There are a great amount of space debris discarded in the orbits around earth. This pollution in space caused by people's spaceflight has threatened the space assets seriously. Some of the debris with the diameter ranging from 1 to 10 cm, should be given priority treatment for processing, due to the latent but fatal threat they induced. Laser space debris removal is becoming an absorbing topic in the realm of science. Among the mechanisms presented, space-based pulsed laser is one of the effective method to eliminate these small debris. Due to the limitation of technics, the short-pulsewidth, great-energy, compact-structure and reliable lasers claimed in the plans reported were hard to be achieved. A creative debris-removing method using space-based free running pulsed laser was proposed. The long pulse duration of the laser advantaged the impulse generation was revealed in a numerical analysis. Comparing with nanosecond pulsewidth laser, both in theory and experiment, "hot metal vapor ejection" was proved to be better than "plasma ejection" at impulse increment and energy utilization. Analyzing with a laser-melting-metal model proposed, the diameter of metal drops ejected were calculated less than 60 μm in general, with the laser power density greater than 5×106 W/cm2. The result demonstrated that the "micro pieces" accompanying the ejection were unable to cause "secondary threat", but accelerated the debris removing in some degree. The study lays the foundation for the application of space-based free running laser in space debris removal.
2021, 50(S2): 20210305.
doi: 10.3788/IRLA20210305
The regular characteristics of the transient response of a silicon-based PIN photodiode were stuidied experimentally, which irradiated by an ultrashort pulse picosecond laser, and the pulse response signals under different laser energy densities were measured. The analysis and experiment results show that with the increase of laser energy density, the device appeares a non-linear saturation state. The FWHM is from 37.2 μs to 113 μs, and the bottom width is from 181 μs to 322 μs. The impulse response signal has a broadening phenomenon, and the signal broadening means that the transient response of the device is degraded. At the same time, the analysis of the half-height width and the bottom width of the signal characteristics before and after saturation shows that whether it is an absolute increase or a relative increase, it can be seen that there is a more significant broadening phenomenon after saturation. It is caused by the attenuation of the speed on the falling edge after the device is saturated. Through theoretical analysis, the change in the concentration of injected photogenerated carriers affects the bipolar transport process, thereby changing the speed of the carrier transport process, resulting in degradation of the device response.
2021, 50(S2): 20210035.
doi: 10.3788/IRLA20210035
RF power supply is an important component in RF-CO2 laser. During the development of a new RF-CO2 laser, due to the mismatch between the laser load and the RF power supply, the power tube of the RF power amplifier is easy to break down and burn out in the debugging process. In order to solve this problem, a RF power supply monitoring platform for RF-CO2 laser, which integrated data acquisition, automatic protection control and visualization technology, was designed. The platform adopted a combination of software and hardware, a control module was embedded in the RF power supply, a data acquisition system and automatic protection system were set up, and combined with the circuit design software platform, the RF power supply data acquisition and protection control was completed. The experimental test shows that the platform can effectively avoid the damage of the power tube of the RF power supply, realize the automatic protection of the RF power supply, complete the data acquisition and remote protection control of the RF power supply system, shorten the debugging period of the RF-CO2 laser, and improve the development efficiency of the whole machine.
2021, 50(2): 20200427.
doi: 10.3788/IRLA20200427
The DMD small near-infrared spectroscopy instrument is widely used in chemical composition analysis and quality inspection for its advantages of fast detection speed, high sensitivity, no damage detection, and miniaturization of portable instruments. However, as the premise of instrument design, optical optimization design of the whole spectral range is the hard work of the system. In this paper, the theoretical design method of the spectroscopic imaging system based on the small near-infrared spectrometer of DMD was studied. The method was designed by using the double-dispensing anti-aberration lens and combining the geometric aberration theory to optimize the design of a small DMD near-infrared spectrometer to reduce the aberration of the entire system. Then, the optical simulation software was used to align the direct imaging system for optical simulation. And ultimately achieve the design simulation requirements. Simulation results indicate that the whole size of the spectrometer is less than 150 mm×150 mm×150 mm, and the resolution is better than 15 nm in the range of 1000-1700 nm in the working band. Therefore, the proposed method can meet the design requirements and has broad application prospects in practical applications.
2021, 50(2): 20200392.
doi: 10.3788/IRLA20200392
The force-exerting laser with tunable frequency difference has a broad application prospect, there are few reports on the thermal drift of frequency difference of this laser, but it is an important application index, especially for the interferometer of lithography machine. The frequency difference of birefringence Zeeman dual frequency laser was assigned through elastic force method, and its states of frequency difference in the drift stage, transition stage and stable stage were observed. The experiments prove that the stability of frequency difference is better than 23 kHz/h, and its repeatability is better than 130 kHz; In addition, this paper also comparatively analyzed the influences of elastic force-exerting elements with different structures or materials on frequency difference. The experiments indicate that the uniformity and stability of the temperature distribution play an important role in the frequency difference thermal drift.
2021, 50(2): 20200385.
doi: 10.3788/IRLA20200385
Spectral beam combining technology based on dichromatic mirror can overcome the limitation of the output power limit of one single-mode fiber laser, which is an effective technical means to obtain laser output with high power and perfect beam quality. Theoretically, the influence of the beam position shift and tilt error on the quality of the combined beam was preliminarily explored. The results show that the beam tilt error has a significant influence on the output characteristics of the combining system. In the experiment, the combining experiment of two narrow linewidth fiber lasers was carried out. Using dichromatic mirrors as the combining element, a high beam quality and common-aperture combining with 2355 W combined output power was achieved, the beam quality factor M2 was 1.9, and the efficiency was greater than 99%, which proves that the dichromatic mirror has high efficiency for both the reflection and transmission cases. The experiment result shows that it is possible to achieve a common aperture laser output with higher power and better beam quality by further increasing the number and power of the channel.
2021, 50(2): 20200342.
doi: 10.3788/IRLA20200342
CdTe core-shell semiconductor quantum dots are being widely explored due to their special nonlinear optics and ultrafast dynamics characteristics that include solar cells, optoelectronic devices, biological labeling, and optics fiber sensing fields. In this work, the six kinds of CdTe/CdS core-shell quantum dots were researched in the different core sizes and shell thicknesses for the nonlinear optics and ultrafast dynamics characteristics. The nonlinear absorption and refraction coefficients of the samples were measured by using Z-scan technology under the action of 400 nm wavelength and 130 fs laser pulse width. The experimental results show that the shell thickness of CdTe/CdS core-shell quantum dots affects the nonlinear absorption and refraction characteristics, in which the nonlinear absorption and refraction coefficients increase with the shell thickness. And the core size mainly affects the nonlinear absorption characteristics, while the nonlinear absorption coefficient decreases with the increase of the core size. At the same time, femtosecond time-resolved transient absorption spectroscopy technology was used to measure the ultrafast dynamics characteristics of the samples under the conditions of 400 nm wavelength, 130 fs pulse width, 1 kHz frequency, and 400 nJ single-pulse energy. The transient absorption spectra and ultrafast dynamics curves were obtained. The results suggest that the rising time of bleaching signal increases with the shell thickness. The decay time of the fast process increases with the shell thickness and core size. The decay time of the slow process increases with the shell thickness. The research reveals the influence of the core size and shell thickness of CdTe core-shell quantum dots on the nonlinear optics and ultrafast dynamics, providing a theoretical basis for the preparation of core-shell quantum dots and the research of the photophysical properties.
2021, 50(2): 20200144.
doi: 10.3788/IRLA20200144
Since there is no atmosphere in space, problems such as atmospheric turbulence and atmospheric attenuation do not exist. Therefore, spaceborne Synthetic Aperture Lidar (SAL) has a better application prospect than ground-based and airborne SAL. In order to verify the feasibility of airborne SAL imaging, a spaceborne SAL imaging model was established, and the coherent accumulation time and PRF were derived. Then, a satellite orbit model was established by using the extrapolation method of the two-body motion. Next, according to the limitation of the radar antenna beam width, the antenna pattern of the lidar was calculated, and a method to obtain the maximum synthetic aperture time was proposed by using the target gain curve's 3 dB beam width. Finally, six kinds of spaceborne SAL imaging modes were established through simulation, and the imaging parameters under different modes were analyzed, which verified the feasibility of spaceborne SAL imaging. The research of this paper lays a foundation for the research of spaceborne SAL imaging algorithm.
2021, 50(2): 20200164.
doi: 10.3788/IRLA20200164
In order to evaluate and analyze performance of spaceborne oceanographic lidar for global ocean optical properties detection, a simulation system for spaceborne oceanographic lidar was developed based on lidar equation and the results of Monte Carlo simulation model. The lidar simulation system consisted of three modules, forward simulation, data inversion and error analysis, which could simulate the whole process of laser emission, transmission and detection. According to the given lidar parameters, the detection signals of 443 nm, 486.1 nm and 532 nm in four typical areas, Mediterranean Sea, Indian Ocean, Southern Ocean and Pacific Ocean, were simulated. The results show that the detection depths of 443 nm and 486 nm are approximately the same and deeper than that of 532 nm. For the given lidar parameters, the detection depths of 486.1 nm wavelength in the Pacific Ocean and the Southern Ocean are 120 m and 70 m, respectively, and the detection depth in the Mediterranean Sea and the Indian Ocean is about 100 m. The detection depths of chlorophyll-a concentration in the above sea areas are about 80 m, 50 m and 70 m, respectively.
2020, 49(8): 20200203.
doi: 10.3788/IRLA20200203
As a large number of abandoned space objects are out of control, they will be in a tumbling state due to the perturbation effects, such as residual angular momentum, light pressure and so on. De-tumbling control of the space objects is probably a safer way before directly capturing them. De-tumbling control techniques for typical space objects at home and abroad was introduced, the concept of de-tumbling by close irradiation of laser with a small spot was proposed, and the main characteristics of laser de-tumbling control were also analyzed. Moreover, based on the pulsed laser ablation impulse coupling effect, the concept of space-based laser de-tumbling analysis was carried out with the typical cylindrical space targets. The results indicate that the laser control method can precisely control the motion posture of the space target. The space-based laser control method proposed in this paper can provide a new method for the de-tumbling control of the spinning space target.
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