Current Articles

2021, Volume 50,  Issue 2

Invited paper
Autofocusing techniques in digital holographic microscopy and their applications (Cover paper) (Invited)
Wang Yu, Wen Kai, Zhang Meiling, Ma Ying, Liu Min, Zheng Juanjuan, Gao Peng
2021, 50(2): 20200530. doi: 10.3788/IRLA20200530
[Abstract](85) [FullText HTML] (11) [PDF 5628KB](21)
Digital Holographic Microscopy (DHM) combines optical interferometry with optical microscopy and hence provides a fast, non-destructive measurement approach for the 3D profiles of reflective samples, or the thickness distributions and refractive index distributions of transparent objects. DHM can automatically refocus the sample under inspection through numerical propagation of the object wave, if the defocusing distance is pre-known. Hence, it has always been being a hotspot in DHM research to automatically determine the defocusing distance. To this end, this paper reviewed the defocusing distance determination approaches based on sharpness metric, energy concentration criterion, amplitude modulus analysis, sparsity measurement, and different illumination modulations based analysis. Once the defocusing distance was identified with the above approaches, automatic focusing of moving samples could be realized, providing a powerful means for real-time observation of dynamic objects. Moreover, the applications of DHM auto-focusing technology in cell imaging, 3D particle tracking, etc were introduced as well.
Design method of infrared microscope optical system with lower aberration compensation
Liu Zhiying, Lv Zhiyang, Gao Liuxu
2021, 50(2): 20200153. doi: 10.3788/IRLA20200153
[Abstract](36) [FullText HTML] (15) [PDF 1727KB](11)
Aiming at the requirements of high resolution and high imaging quality of the microscope system, the general number of pieces of the system is difficult to adjust, so that the system is difficult to match the actual adjustment result and the design result. Therefore, the lower aberration compensation design method was proposed to design the system. At the same time, the sensitivity of each optical component in a system could be reduced. First, a mathematical model of the lower aberration compensation design method was established, and then it was written into ZEMAX programming language (ZPL) macro that could be used to control ZEMAX to optimize the optical system. Finally, an infrared microscope system was taken as an example. Comparing the optimization results before and after the implementation of the lower aberration compensation design method, it was validated that the proposed method was efficient. It is found that the optical system using the lower aberration compensation design method has an outstanding advantage in image quality comparing with the conventional method. The tolerance sensitivity of each component is significantly reduced, thereby improving the stability of the overall optical system effectively.
Three coordinate passive location technology for airborne multiple spectrum camera
Dong Hao, Sun Tuo, Yang Yuliang
2021, 50(2): 20200498. doi: 10.3788/IRLA20200498
[Abstract](20) [FullText HTML] (8) [PDF 2485KB](5)
A large FOV infrared multiple spectrum camera, which contains advance infrared focal plane, acquires large FOV & high resolution multiple spectrum image toward area below the flight vehicle. It takes images on a whole day and nearly a whole whether condition. The multiple spectrum camera system configuration was proposed. Its angular measurement, three coordinate passive location key technology and solution were described in detail. The angular measure electro-circuit & clock synchronization should be finely designed. When the system had been integrated, angular error calibration and compensation, multi-sensor installation attitude calibration were proposed to improve angular measure accuracy and location accuracy. Flight tests shows that image mosaicking accuracy is 10″ which means the technic is effective.
Infrared technology and application
Characteristics and causes of non-effective pixels of HgCdTe FPA
Li Jianlin, Xie Gang, Liu Lian, Chen Xiaoyan, Dong Wei, Lei Yongchang
2021, 50(2): 20200202. doi: 10.3788/IRLA20200202
[Abstract](21) [FullText HTML] (7) [PDF 2160KB](9)
The reduced trend of operable pixel factor of medium wave or long wave infrared focal plane array must be resulted from some failure mechanism caused by manufacturing process defects, specific working stress or environmental stress. Mathematical model based on the output signal voltage of infrared detector, through the analysis of signal transmission and the statistical analysis of performance evaluation test data, visualization means such as statistical graphs, response curves and output signal voltage grayscale were used to visually express non-effective pixel characteristics, such as the types, number, locations, distribution, and output signal voltage, noise voltage, response voltage. Statistical analysis shows that the average apparent operable pixel factor is reduced by 1.07 percentage points relative to the initial operable pixel factor during use of the medium wave 320×250 detector Dewar cooler assembly of pixel pitch 15 μm, 86.45% of apparent non-effective pixels are unstable flickering pixels and drifting pixels on average. Design and manufacturing defects cause the response line of non-effective pixels to be horizontal, and the response voltage tends to 0. The thermal adaptation stress is the reason for non-effective pixel clusters of linear. A method was proposed to screen and identify non-effective pixels based on the criterion that the pixel signal voltage exceeded the average value of ±(6%~7.5%) under different blackbody temperatures.
Long wavelength infrared readout circuit with background suppression function
Zhang Wukang, Chen Honglei, Ding Ruijun
2021, 50(2): 20200266. doi: 10.3788/IRLA20200266
[Abstract](39) [FullText HTML] (12) [PDF 4737KB](13)
In order to improve the sensitivity of target detection by IRFPA, the carrier generated by target radiation should be maintained as long as possible. And the proportion of thermal excitation and background radiation excitation should be reduced as much as possible. The integral capacitance of the long-wave infrared (LWIR) readout circuit (ROIC) is easily saturated under high background conditions. And the non-uniformity of the LWIR detector dark current will affect the fixed pattern noise (FPN) of the focal plane array (FPA). Based on the common mode background suppression (BDS) structure and the analysis of dark current for long-wave HgCdTe detector, the BDS circuit with non-uniformity correction was designed. Traditional background suppression circuits only used common mode background suppression or differential mode background suppression. The high-precision background memory of the differential mode background suppression module was generally within a small range. Common mode BDS and differential mode BDS were used for BDS module in this paper, which can effectively reduce the fixed graphics noise and increase the dynamic range in a larger background noise range. For this background suppression circuit, the common mode background suppression used a voltage-current conversion method, and the differential mode background suppression used a current storage type background suppression structure. The background signal was amplified during background memory and signal was reduced during BDS for differential mode BDS. It could improve BDS accuracy. The circuit adopted standard CMOS process tape out. The test result shows that the FPN of ROIC is 2.08 mV. The FPN of the FPA without background suppression is 48.25 mV. When background suppression is turned on, its FPN noise is 5.8 mV. Based on the detector's non-uniform distribution of dark current, the theoretical FPN value is calculated to be 40.9 mV. The RMS noise of the output signal of the long-wave infrared focal plane is about 0.6 mV.
Preparation and application of a high-performance vanadium oxide thermosensitive film
Ma Zhanfeng, Wang Ying, Wang Chao, Ye Fan, Gao Jianfei, Huang Li
2021, 50(2): 20200349. doi: 10.3788/IRLA20200349
[Abstract](26) [FullText HTML] (8) [PDF 3470KB](9)
A method for preparing high performance vanadium oxide thermosensitive thin films and its application were reported. Using reactive magnetron sputtering film deposition technology, the preparation process of vanadium oxide thin films was optimized by changing the sputtering power during the deposition of vanadium oxide thermosensitive thin films, the deposition rate of vanadium atoms was adjusted when they touched the surface of the substrate after being sputtered. At the same time, the equipment was modified and upgraded, that is, a control power supply outside the vanadium sputtering chamber was added to accurately control the sputtering voltage and oxygen partial pressure and other parameters to accurately control the current density in the reaction process. A vanadium oxide film with a sheet resistance of 500 kΩ/□ and a temperature coefficient of resistance (TCR) of −2.7% K−1 was prepared. The experimental results show that the noise equivalent temperature difference (NETD) performance of uncooled infrared focal plane detector made of high-performance vanadium oxide thermal sensitive film is reduced by 30% and the noise is reduced by 28%. The overall performance of the uncooled focal plane detector has been improved significantly.
Lasers and Laser optics
Principle and optimum analysis of small near-infrared spectrometers based on digital micromirror device
Liu Hongming, Liu Yujuan, Song Ying, Zhong Zhicheng, Kong Lingsheng, Liu Huaibin
2021, 50(2): 20200427. doi: 10.3788/IRLA20200427
[Abstract](36) [FullText HTML] (14) [PDF 1349KB](18)
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.
Thermal drift of frequency difference of frequency splitting laser with force-exerting
Wang Qi, Qian Yongming, Zhang Shulian
2021, 50(2): 20200392. doi: 10.3788/IRLA20200392
[Abstract](12) [FullText HTML] (7) [PDF 1818KB](2)
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.
2.3 kW fiber laser spectral beam combination based on dichromatic mirror
He Xubao, Xiao Hu, Ma Pengfei, Zhang Hanwei, Wang Xiaolin, Xu Xiaojun
2021, 50(2): 20200385. doi: 10.3788/IRLA20200385
[Abstract](40) [FullText HTML] (17) [PDF 1546KB](10)
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.
Nonlinear optics and ultrafast dynamics characteristics of CdTe/CdS quantum dots with different core sizes and shell thickness
Chang Qing, Tan Hengyu, Meng Tianming
2021, 50(2): 20200342. doi: 10.3788/IRLA20200342
[Abstract](25) [FullText HTML] (14) [PDF 3079KB](6)
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.
Parameters analysis of spaceborne synthetic aperture lidar imaging
Yin Hongfei, Guo Liang, Jing Dan, Xing Mengdao, Zeng Xiaodong, Hu Yihua
2021, 50(2): 20200144. doi: 10.3788/IRLA20200144
[Abstract](17) [FullText HTML] (8) [PDF 6176KB](5)
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.
Estimation of chlorophyll profile detection capability of spaceborne oceanographic lidar
Zhu Peizhi, Liu Bingyi, Kong Xiaojuan, Yang Qian
2021, 50(2): 20200164. doi: 10.3788/IRLA20200164
[Abstract](21) [FullText HTML] (11) [PDF 1911KB](3)
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.
Materials and thin films
Study on the design and preparation technology of ultra-low profile wideband high reflection thin films
Bai Jinlin, Jiang Yugang, Wang Lishuan, Li Ziyang, He Jiahuan, Liu Huasong, Su Jianzhong
2021, 50(2): 20200413. doi: 10.3788/IRLA20200413
[Abstract](23) [FullText HTML] (9) [PDF 3779KB](4)
The surface shape deviation of the optical thin film element will cause the wavefront distortion of the transmitted beam in the high-precision laser system, which will seriously affect the performance of the optical equipment. The traditional surface profile deviation control technology uses double-sided coating, but it is necessary to repeatedly polish the substrate to obtain a high-precision surface profile, which will greatly increase the development cost and limit the use of this method. Based on ion beam sputtering deposition technology, a stress-deformation model was used to predict the shape change after coating, and then the coating surface of the component to be plated was pre-processed into a surface shape opposite to the deformation direction, compensating for the deformation of thin film components caused by the stress of the film after coating. Finally, an ultra-low-profile broadband high-reflection film was prepared on the pre-processed substrate to achieve reflectivity R≥99.5% and PV≤0.15λ@632.8 nm at the working wavelength of 550-750 nm. Through calibrating the mechanical parameters of thin film materials, this technology predicts the surface shape changes of any multilayer film under the same process conditions, realizes the introduction of mechanical synchronization design while designing the ultra-wide spectrums, and prepares high-quality optical films that meet the dual indicators of light and force.
Study on infrared anti-reflection performance of diamond film with surface microstructure
Zhang Zhaoyang, Wei Junjun, Xing Zhongfu, Peng Zhiyong, Liu Jinlong, Chen Liangxian, Li Chengming
2021, 50(2): 20200199. doi: 10.3788/IRLA20200199
[Abstract](26) [FullText HTML] (19) [PDF 4009KB](4)
CVD diamond is an excellent material for infrared optical window, but its theoretical transmittance in the infrared band can only achieve about 71%. The optical transmission performance of the CVD diamond film can be improved by the surface sub-wavelength structure design. In this study, the quantitative relationship between diamond microstructure characteristics and optical antireflection was established through theoretical simulation. According to the theory guidance, the CVD diamond film with surface microstructure was fabricated by replicating the Si substrate through MPCVD method to improve the transmittance of diamond in the infrared band. Scanning electron microscope (SEM) was used to observe the surface and microstructure of the original silicon wafer and diamond. The growth layer quality and the nucleation layer quality of diamond were both evaluated by Raman scattering spectrum. Infrared spectrometer was used to test the infrared transmittance of diamond film. The results show that after constructing the microstructure on one side, the transmittance of the diamond film in the 8-12 μm band can be increased from 70% to 76%, which means the surface microstructure can significantly improve the optical transmission performance of diamond film. The non-diamond nucleation layer and the insufficient integrity of surface microstructure may be the main reason for the gap between the experimental results and the theoretical simulation results.
Evolution of sapphire surface nanostructure with distance of impurity target
Bi Qian, Chen Zhili, Liu Yuzhao, Tang Li, Xi Yingxue, Liu Weiguo
2021, 50(2): 20200302. doi: 10.3788/IRLA20200302
[Abstract](44) [FullText HTML] (17) [PDF 3868KB](7)
Electron cyclotron resonance ion source has been employed to etch the surface of sapphire (C-cut), introducing metallic stainless steel impurities to investigate the evolution law and optical properties of the self-organized nanostructure on the sapphire surface at different target distances. The atomic force microscope was used to observe the morphological changes of the sample surface, the Taylor Surf CCI 2000 white light interference surface measuring instrument was used to measure the surface roughness; X-ray photoelectron spectroscopy was selected to characterize the chemical composition. The experimental results indicate that, with the ion beam energy of 1000 eV, the beam current density of 487 μA/cm2, the oblique incident angle of 65°, and the erosion duration of 60 min, the distance between the sapphire sample and the impurity target increases from 1 cm to 4 cm, island-like structures appear on the sample surface and gradually evolve into continuous ripple structures. At the same time, as the target distance increases, the orderliness of the self-organized nanostructures enhances, the longitudinal height gradually decreases, while the spatial frequency is unchanged. There are very few metal impurities on the etched sample surface. The appearance of microstructures has antireflection effect on sapphire. During the ion beam sputtering process, island-like structures promotes the growth of ripple nanostructures but destroys orderliness.
Optical imaging
Real-time processing framework of common-aperture active and passive hyperspectral 3D imaging
He Wenjing, Hu Jian, Chen Yuwei, Pan Miaomiao, Zhu Yunwei, He Ruibin, Li Chuanrong
2021, 50(2): 20200249. doi: 10.3788/IRLA20200249
[Abstract](19) [FullText HTML] (14) [PDF 3525KB](5)
Common-aperture active and passive hyperspectral three-dimensional imaging technology is a new remote sensing detection method, which combines active LiDAR and passive hyperspectral cameras in a single framework with shared optical systems. Thus, the difficulty of heterogeneous data registration is reduced, and the generation of the 3D spectral image by real-time fusion becomes possible. The real-time 3D imaging is characterized by data-intensiveness and computing-intensiveness, and the software and hardware co-design framework for system-on-a-programmable-chip provides a feasible solution to it. At present, the hardware/software partitioning is mostly derived from qualitative and empirical analysis, and it is challenging to achieve a quantitative and optimal design. A system-on-a-programmable-chip processing framework using a multi-objective programming model based on object weight was proposed to tackle this problem. In this processing framework, the graph-theory-based model with Ncut criterion was used to achieve high cohesion and low coupling functional modules partitioning. Then, the performances of functional modules with software fulfilment and hardware fulfilment were thoroughly analyzed and evaluated. Finally, aiming at the design requirement, the proposed multi-objective programming model was used for the hardware/software partitioning scheme. Two optimal hardware/software partitioning schemes based on the speed-first criterion or the power-first criterion were solved quantitatively for different scenarios. The result shows that the speed-first design overperforms an empirical design with an increase of 43.4% in processing speed, a reduction of 53.5% in power consumption.
Research on hybrid domain TDICMOS imaging technology based on imaging time calibration
Liang Nan, Zhai Liyang
2021, 50(2): 20200308. doi: 10.3788/IRLA20200308
[Abstract](20) [FullText HTML] (9) [PDF 1356KB](3)
With the increase of line frequency of high resolution imaging electronics in the field of high resolution space remote sensing, the number of photo-electrons in one integration time is gradually reduced, and the imaging ability of the camera in weak light decreases. In electronics, it is necessary to increase TDI stages to make up for the lack of energy. The traditional digital domain accumulation sensor has many disadvantages, such as excessive noise and low frame rate. The large TDI sensor in charge domain will reduce the charge transfer efficiency and increase image aliasing. Based on TDICMOS imaging with low power consumption and high integration, a new hybrid accumulation method based on charge domain and digital domain was proposed. The main indexes that affect the image quality of weak light imaging were analyzed. Then, aiming at the degradation of image quality between multiple photosensitive units under the mode of hybrid domain accumulation, an imaging time calibration method based on image registration was proposed. Through the interval measurement of multiple photosensitive units and the fine-tuning of imaging signal timing, the mismatch between the large integral series charge motion and the scene motion was effectively improved. Finally, through the roller target test, the effectiveness of the imaging time calibration method was verified. The imaging ability of hybrid domain imaging in weak light was also verified by performance test. The results show that the proposed method in this paper can effectively solve the main bottleneck problem of TDI sensor, provides an effective solution for high resolution remote sensing camera.
Optical design
Design of solar-blind ultraviolet warning optical system with large FOV and large relative aperture
Zheng Guoxian, Jiao Jianchao, Yu Yue, Su Yun, Tang Yi, Nian Wei, Liu Jianfeng
2021, 50(2): 20200260. doi: 10.3788/IRLA20200260
[Abstract](20) [FullText HTML] (7) [PDF 2385KB](12)
Due to its high sensitivity, low false alarm rate, small volume, light weight, simple configuration and without cooling system, solar-blind ultraviolet detecting system is widely used in guidance, communication etc., especially in missile warning. According to the application requirements, a solar-blind ultraviolet warning optical system with large field of view and large relative aperture was designed. Based on the requirements of working distance etc., optical system aperture and other parameters were analized. Combined with the actual situation, the optical system selection and difficulty analysis were carried out. Three methods were used to solve the problem of illumination uniformity, and the design results of solar blind ultraviolet optical system with large field of view and large relative aperture were given. It has fine image quality in working spectrum 0.255-0.275 μm. All elements were designed with sphere and used fused silica only, thus have loose tolerance and are convenient for manufacturing and alignment.
Optical design of freeform Fresnel TIR lens for LED uniform illumination
Hu Tiantian, Zeng Chunmei, Rui Congshan, Hong Yang, Ma Suodong
2021, 50(2): 20200183. doi: 10.3788/IRLA20200183
[Abstract](30) [FullText HTML] (13) [PDF 1637KB](9)
A new design of total internal reflection (TIR) lens was presented which had a freeform Fresnel surface in the central part of the front to improve the heat dissipation capability. Snell's law and the reflection law were applied to construct the freeform refractive surface and the freeform reflective surface for the TIR lens. The freeform refractive surface was transformed into the freeform Fresnel surface with universal design method of Fresnel lens. The simulation result for the freeform Fresnel TIR lens obtained by Monte Carlo ray tracing shows that the far field illumination uniformity of 82.0% and the luminous efficiency of 96.6% are achieved for the light source size of 2 mm×2 mm, in the meanwhile the lens weight is only 21.94 g. The freeform Fresnel TIR lens has nearly 20% reduction in lens weight and volume, only a 2% reduction in luminous efficiency, and no reduction in illumination uniformity compared to the TIR lens without the Fresnel surface. The result indicates that the Fresnelization for freeform surface of TIR lens can significantly reduce the volume and weight of TIR lens and shorten the optical path length, thus effectively improve its heat dissipation efficiency and service life while maintaining a high performance.
Optimization design of secondary mirror for near space telescope
Liu Fengchang, Li Wei, Zhao Weiguo, Wang Kejun, Zhao Haibo, Lin Guanyu
2021, 50(2): 20200178. doi: 10.3788/IRLA20200178
[Abstract](27) [FullText HTML] (11) [PDF 2093KB](7)
According to the requirements of high force-thermal stability and high performance of the near space ball-borne telescope, the design of the secondary mirror assembly was optimized. Although the near-space ball-borne telescope was not as harsh as the rocket launching mechanical environment, its unique flight process was affected by temperature changes and acceleration. At the same time, it had a strict quality requirement due to carry with balloon. Compared with the traditional mirror design method, the method of combining entity optimization and base structure optimization, integrated optimization was used to design the mirror, and introduced comprehensive evaluation factors to optimize the overall performance of the secondary mirror. The performance of the final secondary mirror assembly is good, indicating that the optimization method is effective. Through finite element simulation analysis, it is obtained that the secondary mirror assembly has a rigid body displacement of less than 3 μm, a surface accuracy better than λ/50 under the condition of gravity and temperature change of ±3 ℃. Under 0.02 mm assembly error, the shape accuracy is better than 1 nm. The first-order frequency of the secondary mirror assembly is 203.8 Hz. The 10 g acceleration stress response (35.4 MPa) is far less than the material yield stress. Using this method to optimize can obtain high force-thermal stability, high performance secondary mirror assembly.
Design of Φ450 mm light-weighted SiC mirror subsystem in space-based astronomy telescope
Feng Liangjie, Cheng Pengfei, Wang Wei
2021, 50(2): 20200175. doi: 10.3788/IRLA20200175
[Abstract](35) [FullText HTML] (11) [PDF 1736KB](11)
A Φ450 mm primary mirror subsystem of a space-based astronomy telescope was designed with mass, optical surface distortion and reflectivity requirement. The open-back primary mirror was made of pressure-less sintering silicon carbide, light-weighted at a ratio of approximately 70%. Three side supporting invar flexure bipods were designed to minimize the assembling stress and the thermal stress. The high reflection was obtained from the optical surface cementite. The mirror weighted 7 kg and the reflectivity was 98% after optical polishing. The mirror subsystem was precisely assembled under the strict technical condition. The optical test with interferometer show that the optical surface distortion is less than 0.02λ RMS, which meet the critical optical requirements for the primary mirror of the space-based astronomy telescope.
Focal plane alignment for remote sensing camera with dual focal plane of large field of view interval
Zhong Hui
2021, 50(2): 20200172. doi: 10.3788/IRLA20200172
[Abstract](15) [FullText HTML] (7) [PDF 2665KB](3)
The dual channel array focal plane camera with large field of view interval is rare in the previous types of remote sensing cameras. Since it works in the near-infrared spectrum segment, the alignment method of multi-channel camera previously applied in the visible spectrum segment is no longer applicable. The installation and adjustment method was studied. Firstly, the alignment principle was analyzed from the optical point of view, the mathematical model was abstracted and analyzed in detail, and the system error formula was obtained. In the past, the error of this system was very small and had not been paid attention to, but for the remote sensing camera here, its error had seriously affected the test accuracy. After that, the detailed analysis of the alignment test scheme was carried out, and the test scheme of one-dimensional turntable was proposed. Compared with the two-dimensional turntable scheme, the error source was less, the accuracy was higher, and the resources could be saved. Finally, the actual alignment test and test data processing were carried out to eliminate the influence of system error. The adjustment accuracy of focal plane was 1.0 μm, and the alignment result was better than 0.3 pixels. The star point image curve of focal plane obtained was basically consistent with the theoretical design result. The results show that the test method proposed has high precision and adjustment scheme is reasonable and feasible.
Design of cooled medium-wave infrared polarization imaging optical system
Liu Xingyang, Zhai Shangli, Li Jing, Wang Yang, Miao Feng, Du Hanyu, Zou Chaofan
2021, 50(2): 20200208. doi: 10.3788/IRLA20200208
[Abstract](26) [FullText HTML] (7) [PDF 4272KB](9)
In addition to the advantages of traditional infrared intensity imaging, such as long detection distance, all-weather working and good concealment, infrared polarization imaging technology based on the difference between the target and background polarization characteristics can effectively reduce background interference, suppress background clutter, enhance image contrast, improve signal-to-noise ratio, and has broad application prospects. In order to effectively suppress the background clutter interference in the process of air and sea detection, enhance the target detection ability in fog, haze and smoke, as well as the backgrounds of small temperature differences and low illumination, the design of a four channel aperture sharing medium-wave infrared polarization imaging optical system with a focal length of 240 mm was completed. Tolerance analysis was carried out by using Monte Carlo method to ensure the rationality of the precision of optical system processing and assembly. The results of image quality analysis show that the MTF of the optical system is close to the diffraction limit, aberrations have been effectively corrected, and the imaging quality is good. The influence of Narcissus effect on the imaging quality of the cooled infrared optical system was verified by Narcissus analysis. In addition, the optical system proposed has a compact structure and high transmittance, avoiding the use of aspheric surfaces, and has good processing and assembly technique.
Image processing
Analysis and correction of image distortion in MEMS galvanometer scanning confocal system
Miao Xin, Li Hangfeng, Zhang Yunhai, Wang Famin, Shi Xin
2021, 50(2): 20200206. doi: 10.3788/IRLA20200206
[Abstract](23) [FullText HTML] (8) [PDF 5263KB](7)
Aiming at the distorted confocal images caused by the two-dimensional scanning of MEMS galvanometer during skin imaging by reflectance confocal microscopy, the theoretical analysis of beam deflection was carried out, and the specific shape representation of projection plane scanning image was obtained. It was concluded that the theoretical distortion image was consistent with the real distortion image. The distortion mechanism was clarified and a distortion correction method was proposed. First, the original distorted grating image was recorded, then the center lines of grating were obtained based on the Hessian matrix, after that feature points were picked and datum reference lines were set. Finally, the correction to the distorted confocal images was realized by calibrating the corrections of the two-dimensional pixel distortions using polynomial interpolation based on the least square method and filling the gray value of gap pixels by weighted average method. By the experiment of measuring target with grid distortion, the correction coefficient was the highest and the root mean square error was the lowest after polynomial interpolation of degree 7. Also, the optimal number of 512 rows was 379, accounting for 74%. The residual distortions were accurately evaluated, in two dimensional, the maximum value is 4 pixels, the minimum value was 0 pixel and the average value was 1.15 pixels, so the results were accurate. The experiment of in vivo real-time skin imaging shows that the organizational structure features are more real and accurate after corrections. So this method is effective and feasible, which is helpful for accurate diagnosis of skin diseases.
Target redetection method for object tracking based on correlation filter
Jiang Shan, Zhang Chao, Han Cheng, Di Xiaoqiang
2021, 50(2): 20200182. doi: 10.3788/IRLA20200182
[Abstract](43) [FullText HTML] (27) [PDF 4022KB](9)
In recent years, due to the advantages of fast speed and strong robustness, correlation filter based methods have been developed rapidly in the tracking community. However, when the existing models are used to deal with complex scenes, it is difficult to meet the requirements of practical application. The background aware correlation filter (BACF) suffers from the maximum response weakening problem when handling the challenging scenes, such as rotation of the target appearance, scale variation and out of view, thus result in inaccurate tracking result. In order to tackle these problems, a target redetection method for visual tracking based on correlation filter was proposed. On the basis of the background aware correlation filter, a correlation response detection mechanism was introduced to judge the quality of the tracking result generated by the correlation filter. After detecting the tracking result was not credible, a particle filter resampling strategy was exploited to generate abundant particles which was beneficial to perceive the state of the target, and the center of the target could be redetected. On this foundation, an adaptive scale estimation mechanism was adopted to calculate the size information for the target, by which the final tracking result could be obtained. To validate the effectiveness of the improved algorithm, the extensive experiments on three public datasets: OTB2013, OTB2015 and VOT2016 were conducted, meanwhile, several state-of-the-art trackers: correlation filter and deep learning based trackers were also chosen as comparison, and the performance of all the compared trackers was shown from the aspects of annotated video attributes, tracking accuracy, and robustness of the algorithms. Experimental results demonstrate that the proposed target redetection tracker achieve a favorable performance on these three datasets, meanwhile, it effectively improves the accuracy and success rate of the BACF when handling the challenging situations of target rotation, scale variation, and out of view.
State of health estimation for lithium-ion batteries using recurrent neural networks with gated recurrent unit
Zhang Shaoyu, Wu Chunhui, Xiong Wenyuan
2021, 50(2): 20200339. doi: 10.3788/IRLA20200339
[Abstract](22) [FullText HTML] (9) [PDF 2662KB](4)
As one of the key state parameters of the battery, state of health (SOH) represents the degrees of battery degradation, which is very significant for predicting of battery failure and avoiding unsafe behavior of the battery. The difficulty is to determine the appropriate and high correlation input, and design an appropriate estimation algorithm. Through the study of existing battery aging datasets, it is found that the voltage data during charging is relatively stable, which are regular changes with the aging of lithium-ion batteries. Therefore, the voltage data in the charging process were used as the input for estimating SOH, and under the framework of data-driving, an SOH method based on Recurrent Neural Networks with Gated Recurrent Unit (GRU-RNN) was introduced, which could establish the mapping relations between the time series features of one-dimensional voltage data and SOH. The experimental results on two public battery aging datasets show that the proposed method achieves a mean absolute error of 1.25% and a maximum error of less than 5.62%, which is higher than the existing SOH estimation methods in estimation accuracy.
Infrared small target detection using tri-layer window local contrast
Han Jinhui, Jiang Yawei, Zhang Xiaojian, Liang Kun, Li Zhizheng, Dong Xinghao, Li Nan
2021, 50(2): 20200146. doi: 10.3788/IRLA20200146
[Abstract](38) [FullText HTML] (17) [PDF 2421KB](9)
In infrared (IR) guidance, early warning and other fields, it is of great theoretical significance and application value to detect IR small target with high detection rate, low false alarm rate and high speed. An IR small target detection method based on the tri-layer window local contrast was proposed. The tri-layer window could deal with small targets of different scales by single-scale calculation, so that the detection speed could be accelerated. Meanwhile, the enhancement on the true target and the suppression on the complex background were considered before, during and after the local contrast calculation, so that the detection rate could be improved and the false alarm rate could be reduced. Experiments in some IR sequences and images show that, compared with eight existing algorithms, the proposed algorithm can achieve a better performance on detection rate and false alarm rate, and its average time consumption is only about 1/3 to 1/2 of some multiscale algorithms.
Application of Bernoulli filter in bearings-only tracking scenarios
Shi Guoping, Qian Yece
2021, 50(2): 20200343. doi: 10.3788/IRLA20200343
[Abstract](37) [FullText HTML] (19) [PDF 1467KB](8)
The sensor whose information only contains angle information is called bearings-only sensor, and the target tracking based on bearings-only sensor is called bearings-only tracking (BOT). BOT is an important topic in the field of target tracking and will play an important role in passive target tracking surveillance. Bernoulli filter (BF) is the best single target filter within the Bayesian framework. It can obtain the existence probability of the target and the complete posterior probability density function, and judge the appearance and disappearance of the target. The Bernoulli filter was applied to single target tracking in the bearings-only tracking surveillance, and a bearings-only tracking Bernoulli filter was proposed. In the proposed filter, the angle of the target relative to the sensor and its change rate were used as the state vectors to estimate the existence of the target as well as the target state. At the same time, the particle filter (PF) implementation was proposed, too. The simulation results show that, compared with the ordinary Bernoulli filter, the proposed bearings-only tracking Bernoulli filter can judge the existence of the target better, and the error of the target estimation generated by the filter is smaller. Thus, the proposed filter has better tracking performance and higher tracking accuracy, which can be effectively applied to the passive tracking scenarios.
Photoelectric measurement
Multi-camera fast bundle adjustment algorithm based on normalized matrix dimensionality reduction
Zhu Zijian, Zhang Guiyang, Yang Ming, Huo Ju, Xue Muyao
2021, 50(2): 20200156. doi: 10.3788/IRLA20200156
[Abstract](30) [FullText HTML] (13) [PDF 1699KB](6)
Aiming at the problem of high-precision and fast bundle adjustment of multi-camera systems, a multi-camera fast bundle adjustment algorithm based on normalized matrix dimensionality reduction was proposed. Considering the fixed pose parameter relationship between the master and slave cameras in a multi-camera system, the system pose transformation matrix with the dimension of 3N (number of cameras)×4 was used. According to this matrix, each slave camera parameters could be quickly obtained from the master camera parameters, and the transformation relationship was taken into the bundle adjustment algorithm to get the posture of all slave cameras. For external parameters optimization of all cameras, only the external parameter of main camera need to be updated. So all cameras were bundled as a whole, which made the dimension of the Jacobian matrix and the normalized matrix relatively reduce. The calculation of multiple camera feature images could be implemented in one iteration, so the accuracy and speed of the algorithm have been greatly improved. According to simulation and practical measurement experiments, the optimization accuracy of the proposed algorithm is 15.5% higher than traditional bundle adjustment, and the operation efficiency is improved by 7.8%. These precise results can meet the practical engineering application requirements.
Quantitative detection of rivaroxaban based on far-IR absorbance spectroscopy and Raman spectroscopy
Lv Jiaming
2021, 50(2): 20210038. doi: 10.3788/IRLA20210038
[Abstract](34) [FullText HTML] (15) [PDF 2080KB](4)
Rivaroxaban is a new type of oral anticoagulant, which has the advantages of definite curative effect, good safety and convenient use, so it is often used in the prevention and treatment of venous thromboembolic diseases and stroke prevention of non valvular atrial fibrillation. Due to the concentration of rivaroxaban in patients, it will affect the inhibition of coagulation factor Xa, which leads to individual differences in the clinical response of patients and affects the final treatment effect. In order to use rivaroxaban more reasonably, it is necessary to monitor the concentration of rivaroxaban in human blood or urine. For the clinical needs, based on the advantages of far-infrared fingerprint spectrum and Raman characteristic spectrum in effective identification and quantitative analysis of substances, Fourier transform infrared spectrometer and laser confocal Raman spectroscopy system were used to identify and quantitatively detect rivaroxaban in liquid state. In this paper, the change of far-infrared absorption spectrum of rivaroxaban with its concentration was detected by Fourier transform infrared spectrometer, and then the change of Raman spectrum of rivaroxaban with its concentration was detected by laser confocal Raman spectroscopy system. Finally, the accuracy of far-infrared spectroscopy method and Raman method was compared. After comparison, it is proved that the accuracy of far-infrared detection is 2 times higher than that of Raman spectrum detection. These results are of great significance for the use of rivaroxaban in clinical medicine.