2019 Vol. 48, No. 11
2019, 48(11): 1103001.
doi: 10.3788/IRLA201948.1103001
High-performance optical limiting (OL) is of great importance in laser protection application. Although the research of OL lasts for decades, most existing material can not possess all the desired merits such as low threshold, high linear transmittance, especially broadband and ultrafast respondence. Here, the multi-functional OL in conjugated twistacene was reported through experiments and theory. Results show that broadband OL with fast switching speed can be achieved from 480 nm-700 nm based on effective three-photon absorption. Moreover, low OL thresholds (0.15 J/cm2) and extremely high linear transmittance (92% at 532 nm) are simultaneously observed. All these combined advantages in one material shows tremendous potential in ultrafast laser protection for human eye and photonic devices.
2019, 48(11): 1103002.
doi: 10.3788/IRLA201948.1103002
As a new type of two-dimensional nanomaterial, metal carbide/nitride nanosheets (MXene) exhibits high specific surface area and electrical conductivity, and the composition, layers and thickness of that were flexibly controllable. Mxene materials have great potential applications in energy storage, catalysis, sensing and optics. The nonlinear optical effect and response mechanism of one kind of MXene material, namely Ti3C2TX nanosheets dispersion liquid were studied. It was found that the Ti3C2TX nanosheets dispersion liquid exhibited excellent optical limiting properties for nanosecond pulse laser with 532 nm and 1 064 nm wavelength, and the limiting thresholds were estimated to be 0.14 J/cm2 and 0.12 J/cm2, respectively. By measuring the dependence of nonlinear optical scattering signals on incident light power density, it was found that the optical limiting response of the material mainly originated from the nonlinear scattering effect. Compared with the traditional optical limiting material of C60, the material has the advantages of low optical limiting threshold and wide response wavelength range.
2019, 48(11): 1103003.
doi: 10.3788/IRLA201948.1103003
The Si-Pb binary composite gel glass was successfully prepared by sol-gel method using tetraethyl orthosilicate and lead acetate as precursors to introduce graphene nanosheets (GNSs) into the binary inorganic gel network. The morphology, structure, linear optics and nonlinear optical limiting properties of GNSs/Si-Pb binary composite gel glass were investigated by scanning electron microscopy, Raman spectroscopy, UV-visible absorption spectroscopy and open Z-scan technique. The results show that the GNSs can be successfully doped into the Si-Pb binary gel glass by the hydrolysis polycondensation of the precursor, and the obtained composite gel glass exhibits good uniformity and high transparency. The nonlinear optical limiting properties of GNSs have been significantly improved after incorporated into composite gel glass. Furthermore, the optical limiting properties of composite gel glass can be optimized by adjusting the concentration of GNSs in the glass. The above results provide an experimental basis and theoretical basis for expanding the materialization and deviceization of GNSs in the field of nonlinear optics.
2019, 48(11): 1103004.
doi: 10.3788/IRLA201948.1103004
Antimonene was prepared through liquid phase exfoliation of bulk materials. The as-prepared sample was characterized by scanning electron microscope (SEM), ultraviolet-visible (UV-vis) absorption spectroscopy, and Raman scattering spectroscopy in details. Broad absorption from ultraviolet to visible region was observed in the UV-vis absorption spectra. Two typical peaks assigned to Sb were detected in Raman spectra. A flat typical structure corresponding to two-dimensional materials was observed in microscopic characterization. Then Z-scan technique was utilized to test the third-order nonlinear optical properties of the sample. The as-prepared antimonene exhibited saturation absorption when excited by a laser source with pulse width of 4 ns and wavelength of 532 nm. The nonlinear absorption coefficient was -7.8610-11 m/W. Upon electron irradiation, antimonene was successfully transformed into optical limiting materials, which exhibited reverse saturable absorption with a nonlinear absorption coefficient of 8.6910-11 m/W.
2019, 48(11): 1103005.
doi: 10.3788/IRLA201948.1103005
A series of novel twistace ne-decorated arenes including heterorings (2, 5, 8) were con-veniently synthesized promoted by palladium catalyst in one step and characterized. Compared with the model twistacene 1, all of them exhibited red-shifted absorption spectra with the maximum peaks centered at 462 nm for 2, 478 nm for 5, 468 nm for 8, and emission spectra spectra with the maximum bands at 476/506 nm for 2, 497/527 nm for 5, 497/520 nm for 8 respectively, which belonged to blue and green fluorescence region. The electrochemical properties were carried out through cyclic voltammetry method and molecule 8 displayed a smallest oxidation potential at 0.35 V among them, which resulted from the oxidation of the amine moiety. Their optical limiting properties were examined via femtosecond laser. The results suggest that all of them exhibit high transmittance and 5 possesses excellent optical limiting response.
2019, 48(11): 1105001.
doi: 10.3788/IRLA201948.1105001
Laser diode pumped high-power Yb-doped all-solid-state femtosecond lasers were developed. Firstly, a high-power and high-efficiency Yb:LYSO femtosecond oscillator was realized by passively mode-locking technique using semiconductor saturable absorber mirror. Stable mode-locking operations at 1 035 nm and 1 042 nm with both as high as 3 W average output power were achieved, respectively. The corresponding pulse width was 351 fs and 287 fs, the slope efficiency is 88.2% and 89.7% respectively. Secondly, stable 70 fs pulses with the average power of 2.52 W were directly generated from a high power multimode diode-pumped Yb:CYA laser with Kerr-lens mode-locking technology. By separating the gain medium and Kerr medium, the single pulse energy and the peak power was up to 50 nJ and 0.71 MW, respectively. It is shown that the above erbium-doped crystals have excellent performance in the field of high-power diode-pumped all-solid-state lasers.
2019, 48(11): 1105002.
doi: 10.3788/IRLA201948.1105002
The output characteristics of a-cut Nd:GdVO4 crystal cascaded self-Raman laser based on semiconductor laser end-pumping were reported. Making full use of the excellent laser characteristics and strong Raman gain of Nd:GdVO4 crystal, as well as using broadband high-reflection mirror designed for cascaded Raman operation, second order Stokes laser at 1 309 nm based on the Raman shift of 882 cm-1 was successfully achieved under the acousto-optic Q-switched modulation. Under the incident pump power of 10 W and the pulse repetition frequency of 50 kHz, a maximum average Raman laser output power of 1.48 W and a pulse width of 5.3 ns for 1 309 nm laser was obtained, corresponding the threshold and the conversion efficiency for second order Stokes generation were around 5.9 W and 14.8%, respectively. The results show that cascaded Nd:GdVO4 self-Raman also can achieve high-efficiency second-Stokes laser output, which is of great value to enrich the wavelength of solid-state laser.
2019, 48(11): 1105003.
doi: 10.3788/IRLA201948.1105003
One of the core processes of semiconductor distributed feedback lasers was the fabrication of distributed feedback gratings, and the first-order Bragg grating structure of 808 nm distributed feedback semiconductor was designed. A trapezoidal grating structure with a period of 120 nm was fabricated by using nanoimprint technology combined with process of dry etching and wet etching. The optical field distribution and energy band diagram of epitaxial structure were simulated using MATLAB and Pics3D software. The ideal wet etching process parameters were obtained by optimizing the proportions of corrosion components used in wet etching, corrosion temperature and corrosion time. The scanning electron microscopy measurement shows that the grating has a period of 120 nm, depth about 85 nm, duty cycle about 47%, and the grating has the advantages of straight edges, smooth surface and even period. The innovative introduction of the wet etching process and the corrosion sacrificial layer ensures the cleanliness of the grating surface, improves the secondary epitaxial quality, which lays a good foundation for the further production of high-performance chips for distributed feedback lasers.
Based on the method of energy equipartition and thermal conduction equations and the thermal-elastic equations, a numerical model of the gradient dopant concentrations rod laser medium end-pumped by laser diode was set up. Considering the temperature correlation of the thermodynamic parameters of the material and heat transfer coefficient between air and medium, the distributions of absorption coefficient, absorption pump power, temperature, thermal stress and strain in the laser medium of constant doping, two stepwise gradient doping, five stepwise gradient doping and ideal gradient doping structures were calculated by a finite element analysis method. The results indicate that by using the gradient dopant concentrations laser medium, absorption pump power uniformity in laser medium can be improved greatly. And the maximum temperature and principal tensile stress and principal strain of the five stepwise gradient doping laser medium were respectively 42.6% and 31.9% and 28.1% of the constant doping laser medium. It is obvious that the thermal effects of the gradient dopant concentrations laser medium are greatly reduced. The theoretical results provide theoretical reference and experimental study for the design of solid laser pumped by laser diode.
2019, 48(11): 1105005.
doi: 10.3788/IRLA201948.1105005
In order to study the application of dual-frequency lidar in the detection of hypersonic target, the absorption and attenuation characteristics of laser in plasma were analyzed theoretically. Based on the measured data of RAM-C experiment, the plasma electron density of blunt body model in different hypersonic flight scenarios was obtained by simulation calculation, which verified the accuracy of the calculation. The temperature distribution on the stationary line of blunt body was calculated from 8 000 K to 16 000 K, and combined with theoretical analysis we can obtain laser attenuation in plasma sheath on electron density, temperature and laser frequency, which showed that the absorption of laser by plasma sheath was very small. By comparing the echo signal to noise ratio of dual-frequency laser and single frequency laser in turbulent transmission, the anti-turbulence characteristics of dual frequency laser were obtained. Thus shows that the dual-frequency lidar is an effective way to detect the hypersonic target.
2019, 48(11): 1105006.
doi: 10.3788/IRLA201948.1105006
Recently a high optical efficiency all-fiber coherent Doppler lidar (CDL) system was developed to achieve real-time measurements of wind fields. The coherent lidar worked on 1.55 m band, the diameter of the felescope was 50 mm, the temporal and spatial resolution were 1 s and 30 m respectively. In addition, the system consisted of a fiber-based optical transceiver unit, a 2-axis scanner which can program scanning scheme, and a multicore digital signal processor (DSP) for real-time signal processing. Theoretical performances of the system in wind sensing were estimated and compared with experimental results, it verified that the measurement range was 5 km. In comparative experiment, the system and ultrasonic anemometer measured wind field simultaneously. Measured data were compared and analyzed, the result were listed as follow:correlation coefficient of wind speed was 0.980 and standard deviation was 0.235 m/s; correlation coefficient of wind direction was 0.993 and standard deviation was 3.105. The results prove that the system has excellent performance, can be widely used for wind detection in atomospheric boundary layer.
2019, 48(11): 1105007.
doi: 10.3788/IRLA201948.1105007
In order to improve the angle measurement accuracy of laser seeker, the source of angle measurement error of laser seeker was studied, and the error of direct writing laser seeker calibration system was analyzed. Firstly, the influence of the optical system in the laser seeker and the detector installation error on the angle of the seeker was analyzed. The relationship between the angle of turntable and the angle of seeker under idea conditions was given. Secondly, the working principle of the direct writing laser seeker calibration system was introduced. Thirdly, in order to improve the angle accuracy of the calibrated seeker, the installation error of the calibration system was analyzed. Finally, according the analysis method in this paper, the calibration system error was corrected, and the seeker zero error was reduced to within 1 mrad from 2.5 mrad before the calibration. The conclusions of this paper provides an analytical method for the precision requirement of the structure installation in the direct writing laser seeker calibration system, and thus improves the angular measurement accuracy of the laser seeker after calibration.
2019, 48(11): 1105008.
doi: 10.3788/IRLA201948.1105008
A new Infrared Thermal Wave Nondestructive Testing technology-laser scanning thermography nondestructive testing technology was investigated in this work. A finite element simulation model was built based on the deeply analysis of detection mechanism, and the temperature difference between defect and non-defect was selected to analyze the influence rules of the key parameters such as sample material, defect size, defect depth, laser scanning speed and laser scanning power on laser scanning thermography nondestructive testing technology, which provided a reference for the further development and application of the new technology. The relationship between the parameters and the maximum surface temperature difference were numerically investigated. On this basis, the control strategy of detection parameter in the laser scanning thermography nondestructive testing technology was put forward, which can facilitate to set the detection parameters quickly and accurately for the corresponding defect characteristics of sample in actual detection process, and to improve the detection ability.
InAs/GaSb superlattice material has become the primary choice for the fabrication of the third-generation infrared detectors. Practical researches on detector design, material epitaxy, chip processing, etc were carried out. 320256 dual-color focal plane arrays with excellent performance was fabricated. Firstly, a mid-/short-wavelength dual-color chip structure was designed based on two back-to-back n-i-p junctions with voltage selection structure. Then the PNP superlattice material with complete structure, smooth surface and low defect density was grown by molecular beam epitaxy (MBE). The device was passivated with sulfide treatment and a SiO2 layer. Finally, at 77 K, the RA value of middle-wave channel reached 13.6 kcm2 and the short-wave channel reached 538 kcm2. The spectral response indicated the short-wave response band of 1.7-3 m and the middle-wave of 3-5 m. The middle-wave channel exhibited a detectivity value of 3.71011 cmHz1/2W-1, a photo-response non-uniformity of 9.9% and an effective pixel rate of 98.46%, while the short-wave channel exhibited a detectivity value of 2.21011 cmHz1/2W-1, a photo-response non-uniformity of 9.7% and an effective pixel rate of 98.06%.
2019, 48(11): 1104002.
doi: 10.3788/IRLA201948.1104002
According to the wide spectrum requirement of environmental pollution gases monitoring, a wide spectrum infrared spectrum remote sense method was proposed. By using the long wave infrared Fourier interference spectrum technology, the response band of the instrument was extended to the short wave end of the long wave infrared atmospheric window, so that it can detect the fingerprint characteristics of most common industrial gases under certain conditions. In the 7.0-14.5 m (700-1 450 cm-1), the difference spectrum method and bright temperature method can be used to monitor a variety of commonly used industrial toxic and harmful gases, and the approximate concentration characterized by the long-term product of the concentration range can be given. The performance characterization method of remote sense spectrometer was introduced, and the application examples of PARES100 to 11 kinds of industrial gases and harmful gases were given.
2019, 48(11): 1104003.
doi: 10.3788/IRLA201948.1104003
In the field of target detection, the Single Shot multibox Detector (SSD) target detection network based on deep learning has two advantages of good real-time performance and high accuracy. Because the infrared image of special vehicles was difficult to obtain, the infrared image of car and bus were taken as the research object, the Pascal VOC dataset of infrared image was constructed, the SSD network was trained, and the infrared target image was detected by the trained network. The results show that the more the feature information of the infrared target, the higher the detection accuracy, but the problem of missing detection of the vehicle with missing information exists in the infrared image. In response to this problem, the data structure was optimized by adding the incomplete window module, and the problem of missing detection of the vehicle was effectively solved, and the detection accuracy of the target as a whole was also significantly improved. The infrared target detection result after improving the data set was used as the evaluation index, which can accurately evaluate the infrared stealth camouflage effect of special vehicles under complex background.
2019, 48(11): 1104004.
doi: 10.3788/IRLA201948.1104004
Airborne High-spectral Interferometer Sounder (HIS) is a detector designed to measure the infrared atmospheric background radiation in nadir viewing mode. Based on HIS infrared high-resolution spectral data, sensitivity analysis of atmospheric temperature and major atmospheric absorbers were carried out. By introducing the concept of information content and using the 1D-VAR method, the ability of detecting atmospheric parameters was analyzed with HIS measurment. The information content, degree of freedom and vertical resolution of temperature and water vapor have been used to characterize the observation system. The information content of temperature and water vapor was 49.5 and 25.2 respectively, the degree of freedom was 10.5 and 5.6 respectively, the average vertical resolution of temperature was 2.2 km, and the average vertical resolution of water vapor was 2 km. The relationship between the inversion accuracy and the instrument noise was discussed. It shows the minimum measurable accuracy of retrieved temperature and humidity profile.
2019, 48(11): 1104005.
doi: 10.3788/IRLA201948.1104005
In order to realize large scale, high spatial resolution and high spectral resolution, mechanical assembly technology was usually adopted to realize Long Linear assembly. The large cold plate of 120 mm was achieved through the mechanical assembly technology of two thermoelectric coolings. Packaging of Long Linear InGaA s focal plane array assembly with 4 000 pixels was adoped through the mechanical assembly technology. Temperature uniformity distribution of the Long Linear, the coplanar error of FPAs, and the engineering reliability of the assembly were studied. The temperature uniformity was controlled at 0.4℃, the focal plane array coplanar error was controlled inside 0.020 mm by mechanical assembly of thermoelectronic coolings, thermal analysis, selection of coolings material, tolerance control of component and micro regulation etc. The Long Linear InGaAs focal plane array shortwave infrared assembly had passed the impact and random vibration test, the focal plane array coplanar error was nearly unchanged. At last, a clear ground-imaging in the camera was abtained.
2019, 48(11): 1113001.
doi: 10.3788/IRLA201948.1113001
As an important direction for the future development of star sensors, all-time star sensor technology can extend the application of star sensors to near space platforms such as stratospheric airships and high-altitude balloons. Due to the intense atmospheric background radiation during daytime, the detection capability of star sensors in visible band was significantly limited. The intensity of atmospheric background radiation in the short-wave infrared (SWIR) band was rapidly reduced compared to that in the visible detection band. Therefore, the application of SWIR imaging systems for star detection in the range of 0.9-1.7 m has become an effective solution for studying the all-time star sensor technology. In order to analyze and verify the feasibility of SWIR all-time star sensor, the all-time star sensor detection model was analyzed and the impact of SWIR detector noise on the detection capability was discussed in this paper. Then, the optical parameters of the all-time star sensor at a height of 20 km were determined through simulation calculation. The prototype of the all-time star sensor was developed based on SWIR detector. Combined with the star observation experiments at the ground, the detection performance of the prototype was tested and the correctness of the all-time sensor detection model was verified.
2019, 48(11): 1113002.
doi: 10.3788/IRLA201948.1113002
Time-of-flight measurement is one of the principles of 3D sensation systems. In recent years, with the development of semiconductor technology, time-of-flight measurement systems based on the signal correlation method have developed rapidly in the field of three-dimensional imaging due to its advantages of all solid-state components, high integration and low power consumption. The mathematical principles of correlation time-of-flight measurement techniques were systematically studied, its error sources were analysed, the mathematical models were constructed, and different types of measurement errors were compared. The research results show that light source error, multipath and ambient light interference are the main factors that restrict the measurement accuracy and application range of time-of-flight imaging systems.
2019, 48(11): 1113003.
doi: 10.3788/IRLA201948.1113003
In order to distinguish the scattered light generated by the three defects of micro-particles, sub-surface and micro-roughness existing above the super smooth surface, and to obtain the best region for detecting these three scattering mechanisms, combined the Bidirectional Reflectance Distribution Function (BRDF) with Jones matrix and the polarization coefficients of the three defects were given in the four polarization states ss, sp, ps, pp. On this basis, the relationship between the three defects and scattering azimuth in four polarization states was simulated and analyzed. The results show that these defects could be distinguished by using p-polarized scattering light induced by p-polarized incident light. According to the different relations between the three defects and the variation of scattering azimuth, the best area to distinguish three kinds of defects and its realization methods were given.
2019, 48(11): 1113004.
doi: 10.3788/IRLA201948.1113004
Classification of sea and land returns in airborne lidar was essential for the research of coastal zones and their changing nature. A method for classification using deep learning on the original airborne lidar echo was proposed. A fully connected neural network, and a one-dimensional convolutional neural network (CNN), were used on a training dataset and test datasets from in-situ measurements, and a classification accuracy of 99.6% was obtained. The model was utilized on the datasets from different areas, a classification accuracy of 95.6% was achieved and the processing speed was increased by about 52% compared to support vector machine (SVM) method. The results denote that the deep learning method is very effective for classification of airborne lidar echo waveforms with high precision and speed. It may present further use as a candidate method for classifying species on the sea floor with airborne laser bathymetry.
2019, 48(11): 1113005.
doi: 10.3788/IRLA201948.1113005
Aiming at the problem that the attitude measurement accuracy of Fine Guidance Sensor (FGS) was affected by the error of star point extraction system, a high-precision star point positioning system error compensation method based on Gradient Boosting Decision Tree (GBDT) fitting method was proposed. In order to solve the problems of less fitting samples and large differences in input characteristics, a decision tree that was insensitive to the input range and easy to train was used as the base model. Combining the boosting method in ensemble learning to generate a new base model to obtain the functional relationship between the systematic error and the detector fill rate, sampling window size, Gaussian width of star image and star point centroid coordinate calculation value, and based on this function relationship to the star point centroid. The coordinate estimate was systematically corrected. The experimental results show that compared with the support vector regression machine, the error of the high-precision star point localization algorithm based on GBDT is reduced by 60.6%. The corrected centroid error is 0.014 5 pixel, and the error is reduced by 61.5%.
2019, 48(11): 1114001.
doi: 10.3788/IRLA201948.1114001
The optical surface error is one of the key factors to guarantee the image quality for space telescopes. Increasing aperture and minimizing structural mass result in a relatively lightweight and flexible telescope mirror, whose surface figure is vulnerable to micro-vibration disturbances. Unfortunately, there are a variety of disturbances in space, such as stepper motors, momentum wheels, and cryocoolers. In order to investigate the effect of dynamic optical surface errors on disturbances, a method based on modal superposition and Zernike polynomials (ZPs) fitting was proposed. On the basis of normal mode, the response of an opto-mechanical structure under force excitations could be approximated by the sum of normal modes of the system. For each mode shape, the optical surface could be fitted as a linear combination of ZPs, which were typically used to describe optical surface errors and represent the aberrations of optical systems. Then, modal superposition technique was applied to compute the combined response of surface error. Finally, the dynamic response of optical surface error to disturbances was given in terms of ZPs. So, the influence of disturbances on the aberrations of optical system can be predicted straightforwardly.
2019, 48(11): 1114002.
doi: 10.3788/IRLA201948.1114002
An imaging unit was designed and researched in detail according to the design demands of the space optical remote camera. Firstly, a structure of the imaging unit was proposed, which had smaller size, lighter weight and higher stability. Secondly, in view of the complex working conditions of the optical remote camera electronic device, the protective design method was provided, and an active thermal control method was designed. Finally, the imaging unit was analyzed using FEM. The results show that the imaging unit has a better dynamic performance, as the fundamental frequency of the imaging unit has achieved 184 Hz, which is much higher than the natural frequency 106 Hz of the optical remote camera. The mechanical and thermal stability is higher under the conditions of gravity and 25℃. The mechanical and thermal optical tests are carried out on the imaging unit, and the mechanical test results show that the fundamental frequency of the imaging unit is 185 Hz, which maintains a good consistency with the theoretical analysis result. The thermal optical test results show that the imaging unit has little influence on the thermal optical performance of the whole machine, and all the indicators meet the design requirements.
2019, 48(11): 1114003.
doi: 10.3788/IRLA201948.1114003
To solve the problem of the single thickness of the light-sheet fluorescence microscopy, the design of the variable light-sheet illumination system was carried out based on zoom beam expanding. First, each group of the light-sheet illumination system was calculated using Gaussian optics to obtain the relation between the thickness of the light-sheet and the expansion ratio as well as the relation among the expansion ratio, the lateral magnification and focal length of each group. Then a variable light-sheet illumination system based on 10beam expanding was designed to generate the light-sheet with continuously variable thickness and length. Finally, the parameters and uniformity of the light-sheet and the system tolerance were analyzed. The results show that the thickness of the continuously variable light-sheet is 3.33 m to 33.3 m, and the illumination uniformity is 0.65, 0.4 and 0.61 on the YOZ plane within 60% light-sheet height at low (1), medium (6) and high (10) expansion ratios, respectively. Tolerance analysis shows that the maximum change of the light-sheet thickness is less than the 15% of design value at expansion ratio of 1, less than 6% at 6and 10. The design realizes the continuous variation of the light sheet thickness, and the region of 60% light-sheet height is favorable for the observation of the sample.
2019, 48(11): 1114004.
doi: 10.3788/IRLA201948.1114004
In order to meet the long-term observation requirements of the Earth-Moon imaging spectrometers mounted on the high-altitude balloon platform, the thermal design was presented. The corresponding thermal environment of the load system was analyzed, the heat transfer model of the load system was established, and the sensitivity analysis of the main parameters affecting the temperature level of the load system was carried out by using Spearman rank correlation coefficient formula and the BP-Garson method combining backpropagation neural network with Garson formula. The thermal control pattern of the load system was depicted clearly. In addition, the finite element model of the load system was built and the spectrometers' two working conditions, the December solstice and the June solstice conditions, was simulated by using the I-DEAS/TMG software. The simulation results indicate that under two working conditions, the spectrometers can quickly cool down to -5℃ within 2 h, and the spectrometers maintain the temperature level of (-52)℃ for more than 3.5 h, the optical window temperature is higher than the local dew point temperature at the altitude of 20 km, which satisfies the requirements and the thermal design is reasonable. The research jobs could give some guidance and reference for other ball-loaded optical remote sensors.
2019, 48(11): 1114005.
doi: 10.3788/IRLA201948.1114005
To meet the requirements of high-resolution, high-illuminance uniformity, long working distance and continuous zoom projection of engineering projectors based on TIR prisms, a new method for continuous zoom and high-resolution telecentric projection lens design was proposed. The focal length of the designed projection lens with F/2.4 ranged from 25 mm to 32 mm, and the lens was specialized for the visible light application. The properties of the large target surface, high-resolution, long working distance and good illumination uniformity were the main difficulties in the projection lens design. The double Gaussian model with anti-distance was chosen as the initial structure. Then a specialized control strategy for image telecentric was employed. The whole design process was conducted in CODE V associated with the expert automatic optimization strategies, such as the choice of the types of different glasses. The results show that the value of MTF within the view fields is no less than 0.4 at 72 lp/mm, the diameters of RMS diffuser is less than 8.5 m, the distortion is under 2%, and uniformity of field of view of the short focal edge is greater than 95%. The projection lens designed with spherical surfaces show the compact structure and well image quality. The key points, such as distortion, vertical axis chromatic aberration and illuminance uniformity, are also well controlled in this design, which demonstrates that the designed project lens can meet the requirements of high-resolution engineering projectors well.
2019, 48(11): 1118001.
doi: 10.3788/IRLA201948.1118001
In order to solve the technical problem of bearing load on both ends of the optical antenna, a loadable laser communication optical antenna for satellite platform was proposed, and at the same time guaranteed the imaging quality of the one point to multi-point laser communication terminal optical antenna. In order to ensure the surface accuracy of the primary mirror and the position accuracy of the secondary mirror, the structure and connection form of the primary mirror assembly, the loadable baffle and the secondary mirror support truss were optimized. Using ANSYS finite element analysis software for analysis, the results show that the first-order mode frequency of this structure is 151.54 Hz; The front end of the optical antenna can carry the quality of 8.5 kg and the rear end of the antenna can carry the quality of 13 kg; Under the condition of 1 g radial self-gravity and bearing load at both ends,the RMS (root mean square error) value of surface shape error of the primary mirror is /158, PV (maximum peak-to-valley error) value is /30, the maximum inclination of the secondary mirror is 1.88; Under the condition of (205)℃ ambient temperature, 1 g axial self-gravity and bearing load at both ends, the RMS of the primary mirror is /65 and the PV is /14, the maximum inclination of the secondary mirror is 1.21. It shows that the antenna has good mechanical properties, thermal properties and imaging quality after being loaded. It can meet the requirements of the antenna in the installation, detection and transmission of the ground. The ZYGO interferometer was used for testing. The quality of the load and the position of the center of gravity were simulated by the mass. The results show that the system wavefront aberration of the system RMS can meet the index requirements of /15 under the condition of 1 g gravity and load.
To satisfy the application of fiber grating sensor technology in high vacuum thermal environment, FBG on two different kind of sleeve compactly single model fiber covered by acrylate and polyimide were researched. Influence of the cover on the peak wavelength power of FBG in high vacuum thermal environment was analyzed and verified. Firstly, experimental program of influence on FBG reflection spectrum characteristics was designed and then a hardware-in-the-loop detection platform was set up. Finally, the influence of temperature and vacuum on the reflection peak power of FBG in different coating single-mode transmission fiber under high vacuum thermal environment was studied and verified. Experimental results indicated that:when vacuum varied from normal pressure to 10-4 Pa level and then return to normal pressure, temperature of two different coating single-mode transmission fiber dropped to -196℃ from room temperature and then returned to room temperature, after 224 hours, the peak power of the FBG reflectance spectrum did not change. It provides the theoretical and experimental basis for the application of optical fiber sensing technology in high vacuum (pressure about 10-4 Pa level) and thermal environment (-196-25℃ temperature cycle).
2019, 48(11): 1118003.
doi: 10.3788/IRLA201948.1118003
The enhanced temperature sensitivities of Fiber Bragg Gratings (FBGs) slice-packaged with copper, aluminum, perspex and PTFE were studied experimentally. The results show that when the coated fiber tails on both sides of FBG are bonded on substrate materials, the temperature sensitivity coefficients are about 2.3 times, 2.9 times, 5.2 times, and 11.7 times that of a bare FBG, respectively. However, the measurement reproducibility of the results is unsatisfactory due to the fact that the thermal expansion of substrate materials at higher temperature will inevitably lead to a separation of fiber cladding from coating layer. For experimental optimization, the experiments under the uncoated tail of FBG are carried out based on the aforementioned four substrate materials. The reflection wavelengths have a good linear relationship with the temperature change within the measurement temperature range. The temperature sensitivity coefficients of FBGs are enhanced to 3 times, 3.4 times, 9.2 times, 12.6 times, respectively,and the results show a good measurement reproducibility. The research results provide necessary and useful data support and reference for the future research on the temperature sensitivity enhancement of slice-packaged fiber Bragg grating sensors.
2019, 48(11): 1125001.
doi: 10.3788/IRLA201948.1125001
In order to measure and image the ultrasonic wavefield in the whole non-contact field, the dynamic ultrasonic wavefield measurement and imaging method based on digital holographic interference was proposed. Based on the theoretical analysis of ultrasonic wavefield measurement, the principle of ultrasonic wavefield measurement based on digital holographic interferometry was studied. At the same time, the main measuring process and data analysis process for different cross-sectional of dynamic ultrasonic wavefield were studied. The reflection type digital holography system based on pulsed laser was designed, including optical detection subsystem, ultrasonic subsystem and synchronization control subsystem. The experimental results show that the dynamic ultrasonic wavefield can be measured and imaged at different moments in a time series. At the same time, the micro-defect sample is designed and detected by dynamic ultrasonic wavefield measurement. The experimental results show that the dynamic ultrasonic wavefield measurement method and system studied in this paper can effectively identify the minor internal defects in the specimen.
2019, 48(11): 1125002.
doi: 10.3788/IRLA201948.1125002
In view of the new features of super agile remote sensing satellites, including large angular velocity of 6()/s, large angular acceleration of 1.5()/s2, and the imaging parameters tending to change in different time and space, super agile maneuvering imaging characteristics were analyzed and imaging parameters were simulated. The variation of resultant velocity was precisely calculated based on the complicated model of maneuvering imaging. On this basis, together with the computational formula of SNR and MTF, the change of line rate, TDI stages, MTF of attitude stability, MTF of synchronization error, and MTF of drift error with the variation of the maneuvering angular velocity in different imaging conditions were comprehensively analyzed, which provides an important foundation for the design of super agile maneuvering imaging satellites, particularly for the imaging electronics of the satellites.
2019, 48(11): 1117001.
doi: 10.3788/IRLA201948.1117001
Evaporation characteristics and optical constants of LaF3 materials in 2.5-12 m infrared band were investigated. With low refractive index LaF3 materials, high-durability antireflection (AR) coatings in 3.7-4.8 m medium-wavelength infrared bands were designed and fabricated on Ge substrate. SEM image of the AR coatings with the LaF3 shows that the surface nanocrystals is uniform and densified. The measured optical properties by Fourier tranform infrared spectrometer indicate that the peak transmittance is as high as 99.4%, and the average transmittance increases to 98.8% from 47.7% in 3.7-4.8 m after double-sided coating. The firmness and durability environmental tests signify that this AR coating can work in harsh environment while maintaining good optical properties.
2019, 48(11): 1117002.
doi: 10.3788/IRLA201948.1117002
The technology of magnet-assistant pulsed laser deposition was advanced. A magnetic field whose magnetic lines pointed to the substrate was fixed around the silicon substrate when the diamondlike carbon(DLC) film was prepared by pulsed laser deposition(PLD), so that the ions those flied outside of the substrate were drove to fly to the substrate potentially and participate in the course of filming. The concentration of the ions increased based on the centralization of the ions, and the content of the non-electriferous granule reduced indirectly. Compared with the DLC film prepared without magnetic field, not only the deposition velocity of the DLC film prepared under magnetic field increased sharply, but also the mechanical hardness improved. Of the most importance, this research testified to the high efficiency of the ionization by the laser to the target, offering the base of the feasibility to the combinability between the technologies of the PLD and filtration by magnetic field.
2019, 48(11): 1126001.
doi: 10.3788/IRLA201948.1126001
In a typical polarimetric dehazing method, the estimation of the degree of polarization (DoP) of the backward scattered light is a key factor to affect the dehazing effect. In the present paper, based on the polarization maintaining characteristic of the circularly polarized light in the Mie scatting media, the traditional polarimetric dehazing method was optimized which was suitable for use in the strong scattering environment. The variation patterns of the DoP of the light field received by the CCD, in the light source illuminations with different polarization states and in different densities of the scattering particles, were discussed, based on which a simple and easy method for estimating the DoP of the scattered light was proposed. This method can improve the effect of polarimetric dehazing method, without increasing the complexity of the system. It can be seen from the experiment results that under a condition of strong scattering, the present method can provide the dehazed images with an EME value being 20.4% higher than that by the traditional method. In addition, in this method, it is not necessary to determine the background region (s) as in the traditional method for polarimetric dehazing, thus lowering the calculation complexity.
2019, 48(11): 1126002.
doi: 10.3788/IRLA201948.1126002
Aiming at the problem of limited measurement area in digital holography, a splicing algorithm based on optimized Harris corner algorithm was proposed to realize phase bidirectional splicing. In the process of acquiring digital holographic images, it was ensured that adjacent regions had a certain overlapping portion, and the phase images of the sub-apertures of the obtained objects were spliced; the Harris corner algorithm was used in the splicing to select the corner-dense regions as matching templates, which was efficient and accurate to determine the overlapping region, combined the Gaussian scale space and the pyramid matching idea to optimize the algorithm, and the phase splicing of the 3-D surface reconstruction was realized by weighted fusion. Taking the glass template as the experimental object, the bidirectional splicing of the phase of the object reproduction was completed. The experimental results show that the splicing method could effectively enlarge the measurement area of digital holographic objects and ensured high splicing accuracy.
