2011 Vol. 4, No. 2
2011, 4(2): 93-102.
Abstract
PDF 884KB
Abstract:
Electron trapping materials have been more widely used in the areas of radiation dosimetry, optical information processing, optical storage and infrared detection, etc.. This paper reviews the mechanism of photostimulated luminescence, material types, preparation methods and research progress of the electron trapping materials. On the basis of the applications of the materials to infrared detection, it points out that the detected infrared laser wavelength could exist a detecting threshold under the room temperature. For the shortcomings of the materials in unstable property and easy to cause environmental pollution by the sulphide in preparation processing, it suggests that the preparating method should be improved. Moreover, it emphasizes that the electron trapping materials based on glass ceramics will be promissing materials and prospects the future development of the materials.
Electron trapping materials have been more widely used in the areas of radiation dosimetry, optical information processing, optical storage and infrared detection, etc.. This paper reviews the mechanism of photostimulated luminescence, material types, preparation methods and research progress of the electron trapping materials. On the basis of the applications of the materials to infrared detection, it points out that the detected infrared laser wavelength could exist a detecting threshold under the room temperature. For the shortcomings of the materials in unstable property and easy to cause environmental pollution by the sulphide in preparation processing, it suggests that the preparating method should be improved. Moreover, it emphasizes that the electron trapping materials based on glass ceramics will be promissing materials and prospects the future development of the materials.
2011, 4(2): 103-110.
Abstract:
Grating parameter measurement technology is a key evaluation criterion of grating fabrication. This paper introduces several kinds of grating measuring methods that have been relative mature in present. It focuses on the Atomic Force Microscopy(AFM) method, Scanning Electron Microscopy(SEM), Laser Diffraction(LD) method and scattering measuring method(ellipsometry), and describes their working principles, developing trends and their own advantages and disadvantages. It points out that the AFM and SEM methods can measure the local profile of a grating and can get its surface profile defect. The LD method and scattering method can reflect average results of a laser radiation region, in which the LD method can give the grating period parameters and the ellipsometry can offer the other parameters except the period parameters. Furthermore, the grating parameters gotten by these method are identical, and the LD method provides a minimum uncertainty, the AMF method comes second and the SEM is the last one. In the end, it discusses the developing directions of grating parameter measurement technologies.
Grating parameter measurement technology is a key evaluation criterion of grating fabrication. This paper introduces several kinds of grating measuring methods that have been relative mature in present. It focuses on the Atomic Force Microscopy(AFM) method, Scanning Electron Microscopy(SEM), Laser Diffraction(LD) method and scattering measuring method(ellipsometry), and describes their working principles, developing trends and their own advantages and disadvantages. It points out that the AFM and SEM methods can measure the local profile of a grating and can get its surface profile defect. The LD method and scattering method can reflect average results of a laser radiation region, in which the LD method can give the grating period parameters and the ellipsometry can offer the other parameters except the period parameters. Furthermore, the grating parameters gotten by these method are identical, and the LD method provides a minimum uncertainty, the AMF method comes second and the SEM is the last one. In the end, it discusses the developing directions of grating parameter measurement technologies.
2011, 4(2): 111-117.
Abstract:
Photoacoustic Imaging Technology(PAT) with high contrast, excellent resolution and deep penetration is an emerging noninvasive detecting technology in biomedical applications. This paper introduces the latest progress in PAT, which contains the improvement of image detecting modes, increase of imaging speed, enhancement of imaging resolution and the modification of image reconstruction algorithm. By taking application of PAT to the clinical diagnosis as examples, it describes that the PAT applications have been expanded in biomedical fields. Finally, it overviews the shortcomings of the PAT, and points out that multi-mode combination will a developing trend of the PAT, such as combination of the photoacoustic imaging and the ultrasonic imaging or the photoacoustic imaging and the OCT. Moreover, the molecular PAT based on the contrast agent will also has a good prospect.
Photoacoustic Imaging Technology(PAT) with high contrast, excellent resolution and deep penetration is an emerging noninvasive detecting technology in biomedical applications. This paper introduces the latest progress in PAT, which contains the improvement of image detecting modes, increase of imaging speed, enhancement of imaging resolution and the modification of image reconstruction algorithm. By taking application of PAT to the clinical diagnosis as examples, it describes that the PAT applications have been expanded in biomedical fields. Finally, it overviews the shortcomings of the PAT, and points out that multi-mode combination will a developing trend of the PAT, such as combination of the photoacoustic imaging and the ultrasonic imaging or the photoacoustic imaging and the OCT. Moreover, the molecular PAT based on the contrast agent will also has a good prospect.
2011, 4(2): 118-123.
Abstract:
In consideration of the effects of the mass and sizes of primary mirrors on the load sensitivity, mirror processing and the cost of space remote sensors, the necessity of lightweight for primary mirrors in space remote sensors was introduced, and the lightweight technology was comprehensively summarized. The general rule of the lightweight technology for primary mirrors was described, the different methods of lightweight were compared and the formula for a grid size were given. For a practical project, a SiC primary mirror with half symmetric sandwith structure and a triangular aperture was designed by the iterative method. It overcomes the shortcomings of traditional design method and realizes a single mirror with light mass and excellent rigidity. This method provides a reference for the lightweight technology of large-aperture SiC primary mirrors for the future.
In consideration of the effects of the mass and sizes of primary mirrors on the load sensitivity, mirror processing and the cost of space remote sensors, the necessity of lightweight for primary mirrors in space remote sensors was introduced, and the lightweight technology was comprehensively summarized. The general rule of the lightweight technology for primary mirrors was described, the different methods of lightweight were compared and the formula for a grid size were given. For a practical project, a SiC primary mirror with half symmetric sandwith structure and a triangular aperture was designed by the iterative method. It overcomes the shortcomings of traditional design method and realizes a single mirror with light mass and excellent rigidity. This method provides a reference for the lightweight technology of large-aperture SiC primary mirrors for the future.
2011, 4(2): 124-128.
Abstract:
As more and more small satellites and debris appeare in low orbits, it presentes a big challenge to ground-based detecting and tracking techniques for those objects with fewer effective reflecting areas and high speeds. In this paper, the present status of detecting and tracking techniques for small objects in low orbit is analyzed. An automotive truck-based telescope with a large Field of View(FOV) is designed to search/track micro satellites and small debris. The optical system and system mount in the telescope are introduced and its working mode and data processing are described. Finally, it discusses searching and detection abilities of the proposed system. The obtained results show that the telescope has the capability to search 13.5 magnitude objects(5 cm object in diameter) at the 300 km altitude orbit. It can satisfy the requirements of searching and tracking micro satellites and small debris in low earth orbits.
As more and more small satellites and debris appeare in low orbits, it presentes a big challenge to ground-based detecting and tracking techniques for those objects with fewer effective reflecting areas and high speeds. In this paper, the present status of detecting and tracking techniques for small objects in low orbit is analyzed. An automotive truck-based telescope with a large Field of View(FOV) is designed to search/track micro satellites and small debris. The optical system and system mount in the telescope are introduced and its working mode and data processing are described. Finally, it discusses searching and detection abilities of the proposed system. The obtained results show that the telescope has the capability to search 13.5 magnitude objects(5 cm object in diameter) at the 300 km altitude orbit. It can satisfy the requirements of searching and tracking micro satellites and small debris in low earth orbits.
2011, 4(2): 129-138.
Abstract:
To ensure the operating temperature of electronic controlling cabinet in a space camera to satisfy the operating requirements, the thermal design of large power consumption electronic components in the electronic controlling cabinet was performed according to the design feature and heat transfer path of the controlling cabinet. The key problems such as the great heat-producing capability and long heat transfer path were settled. On the basis of the above, a complete thermal design scheme was given. By taking some classical elements for examples, the effect of heat eliminating was estimated. In the end, a thermal analysis finite element model was established by a finite element thermal analysis software IDEAS-TMG. Based on the given temperature boundary condition, the steady-state thermal analysis of electric cabinet was carried out by the IDEAS-TMG, and the integral thermal response performance of electronic controlling cabinet and the steady-state temperature profiles of PCBs and large power consumption elements were given. It is shown that the ranges of temperatures of PCBs and large power consumption electronic components in steady-state thermal analysis are 40.6-51.1 ℃ and 46.3-62.5 ℃, respectively, which reaches the target of thermal design. Analytical results indicate that the thermal design scheme for the electronic controlling cabinet is appropriate and feasible and it can satisfy the requirement of thermal control operating.
To ensure the operating temperature of electronic controlling cabinet in a space camera to satisfy the operating requirements, the thermal design of large power consumption electronic components in the electronic controlling cabinet was performed according to the design feature and heat transfer path of the controlling cabinet. The key problems such as the great heat-producing capability and long heat transfer path were settled. On the basis of the above, a complete thermal design scheme was given. By taking some classical elements for examples, the effect of heat eliminating was estimated. In the end, a thermal analysis finite element model was established by a finite element thermal analysis software IDEAS-TMG. Based on the given temperature boundary condition, the steady-state thermal analysis of electric cabinet was carried out by the IDEAS-TMG, and the integral thermal response performance of electronic controlling cabinet and the steady-state temperature profiles of PCBs and large power consumption elements were given. It is shown that the ranges of temperatures of PCBs and large power consumption electronic components in steady-state thermal analysis are 40.6-51.1 ℃ and 46.3-62.5 ℃, respectively, which reaches the target of thermal design. Analytical results indicate that the thermal design scheme for the electronic controlling cabinet is appropriate and feasible and it can satisfy the requirement of thermal control operating.
2011, 4(2): 139-146.
Abstract:
In order to maintain the temperature of a space optical remote sensor in orbit, a thermal control system was designed according to a thermal control strategy that was based on the passive thermal control and aided with the active thermal control. Firstly, based on the work patterns of the space optical remote sensor, a modal for its flux calculation was established. Three extreme conditions were confirmed after analysis on the thermal flux and temperature boundary conditions of the sensor. Then, thermal design was concentrated on the sun-oriented work pattern in a low-temperature condition primarily. Finally, the thermal simulation and thermal test for thermal control system were performed. Simulation and test results show that the temperature fluctuations of mirrors are at (181.5) ℃ and the axis temperature difference meets the requirements of the optical system. The temperature of CCD device can be controlled between 18 ℃ and 26 ℃. The results demonstrate that the thermal design is feasible and these experiments can provide a reference for the thermal design of other optical remote sensors with low energies and big optical windows.
In order to maintain the temperature of a space optical remote sensor in orbit, a thermal control system was designed according to a thermal control strategy that was based on the passive thermal control and aided with the active thermal control. Firstly, based on the work patterns of the space optical remote sensor, a modal for its flux calculation was established. Three extreme conditions were confirmed after analysis on the thermal flux and temperature boundary conditions of the sensor. Then, thermal design was concentrated on the sun-oriented work pattern in a low-temperature condition primarily. Finally, the thermal simulation and thermal test for thermal control system were performed. Simulation and test results show that the temperature fluctuations of mirrors are at (181.5) ℃ and the axis temperature difference meets the requirements of the optical system. The temperature of CCD device can be controlled between 18 ℃ and 26 ℃. The results demonstrate that the thermal design is feasible and these experiments can provide a reference for the thermal design of other optical remote sensors with low energies and big optical windows.
2011, 4(2): 147-153.
Abstract:
For the shortcomings of the interference fringe difficult to read and adjust in an Ubbelohde interferometer, a He-Ne laser was used in the Ubbelohde interferometer as the source to offer interference fringe signals with high quality. Then, the fringe signals were transform into electron signals to implement the micro-displacement measurement precisely. A detection circuit was designed and the square wave signal was extracted by using a dual-threshold shaping circuit, which solveed the error processing problem when signals jittered near the set comparison value. A discerning direction and subdividing circuit was designed and the orthogonal electron signals were extracted to achieve the discerning direction of interference fringe movement and the subdivision of interference signals. On the schemes above, a laser interference detection device was designed and built. The device was calibrated by two standard gauge blocks with a difference value of 5 m. Under four subdividing circuits, the resolution of the detecting device is 79 nm. Therefore, the Ubbelohde interferometer achieveds automatic reading and improves its measurement precision.
For the shortcomings of the interference fringe difficult to read and adjust in an Ubbelohde interferometer, a He-Ne laser was used in the Ubbelohde interferometer as the source to offer interference fringe signals with high quality. Then, the fringe signals were transform into electron signals to implement the micro-displacement measurement precisely. A detection circuit was designed and the square wave signal was extracted by using a dual-threshold shaping circuit, which solveed the error processing problem when signals jittered near the set comparison value. A discerning direction and subdividing circuit was designed and the orthogonal electron signals were extracted to achieve the discerning direction of interference fringe movement and the subdivision of interference signals. On the schemes above, a laser interference detection device was designed and built. The device was calibrated by two standard gauge blocks with a difference value of 5 m. Under four subdividing circuits, the resolution of the detecting device is 79 nm. Therefore, the Ubbelohde interferometer achieveds automatic reading and improves its measurement precision.
2011, 4(2): 154-160.
Abstract:
To resolve the problems existed in the estimation of motion in video sequences, a novel method combining the gray projection in a spatial domain and the phase correlation in a frequency domain was proposed. Firstly, the gray projection algorithm was adopted to coarsely register images to entire pixel accuracy, which calculates the gray correlation function for the spatial domain in row and column orientations and obtains the pixel-level motion vector between two sequential images by comparing correlation characters. Then, the phase correlation algorithm was adopted to refinedly register images to sub-pixel accuracy, which uses power spectrum information of images to decrease the image dependence. Furthermore, the fitting method of paraboloid surface based on least-square was used to fulfill the estimation of image displacement parameters. To verify the algorithm experimentally, some samples were simulated. The results show that this method can detect the displacement parameters accurately and efficiently, and can offer the image displacement in a accuracy of 0.01 pixel and the maximum registration error less than 0.004 8 pixel.
To resolve the problems existed in the estimation of motion in video sequences, a novel method combining the gray projection in a spatial domain and the phase correlation in a frequency domain was proposed. Firstly, the gray projection algorithm was adopted to coarsely register images to entire pixel accuracy, which calculates the gray correlation function for the spatial domain in row and column orientations and obtains the pixel-level motion vector between two sequential images by comparing correlation characters. Then, the phase correlation algorithm was adopted to refinedly register images to sub-pixel accuracy, which uses power spectrum information of images to decrease the image dependence. Furthermore, the fitting method of paraboloid surface based on least-square was used to fulfill the estimation of image displacement parameters. To verify the algorithm experimentally, some samples were simulated. The results show that this method can detect the displacement parameters accurately and efficiently, and can offer the image displacement in a accuracy of 0.01 pixel and the maximum registration error less than 0.004 8 pixel.
2011, 4(2): 161-168.
Abstract:
With the particular research on infrared and color visible images, a color image fusion algorithm based on Luminance-contrast Transfer(LCT) technique is presented. Firstly, the method employs a grayscale fusion approach to fuse the infrared image and the luminance component of the color visible image. Then, it uses the LCT technique to improve the luminance and contrast of the grayscale fused result. Finally, the color fused image is generated directly in the RGB space with the fast YCBCR transform fusion scheme. Two different strategies which employ the pixel averaging fusion approach and the multiresolution fusion approach as the grayscale fusion solution are proposed to implement the high real-time and high fusion quality, respectively. Experimental results show that the proposed algorithm can produce a color fused image not only with the natural color appearance similar as that of the input color visible image, but with pleasing luminance and contrast, and can also provide a good result even using the pixel averaging scheme to implement the grayscale fusion.
With the particular research on infrared and color visible images, a color image fusion algorithm based on Luminance-contrast Transfer(LCT) technique is presented. Firstly, the method employs a grayscale fusion approach to fuse the infrared image and the luminance component of the color visible image. Then, it uses the LCT technique to improve the luminance and contrast of the grayscale fused result. Finally, the color fused image is generated directly in the RGB space with the fast YCBCR transform fusion scheme. Two different strategies which employ the pixel averaging fusion approach and the multiresolution fusion approach as the grayscale fusion solution are proposed to implement the high real-time and high fusion quality, respectively. Experimental results show that the proposed algorithm can produce a color fused image not only with the natural color appearance similar as that of the input color visible image, but with pleasing luminance and contrast, and can also provide a good result even using the pixel averaging scheme to implement the grayscale fusion.
2011, 4(2): 169-174.
Abstract:
In order to solve the contradiction between veracity and validity for calculating the three-dimensional target electromagnetic scattering, a calculator mode about Finite Element-Boundary Integral(FE-BI) was set up to calculate the three-dimensional target electromagnetic scattering. Firstly, the three-dimensional target electromagnetic scattering calculation borderline integral was analyzed, and the vector Green function was introduced. On the basis of the connection between electromagnetism form and three-dimensional cavity form, the three-dimensional hatch cavity borderline mode was set up. Then, the finite element commonly function was established by combining the optical target surface modeling method with the higher order function method, and the application of the FE-BI to calculating three-dimensional target electromagnetic scattering was achieved. Finally, the following example analysis was proved. It is shown that the angle tally is very ideal when the dimensional bosom is empty or anisotropic matter. The consistance has been 90% as compared with the traditional matching method. In conclusion, the veracity and validity of calculation are improved by the proposed method.
In order to solve the contradiction between veracity and validity for calculating the three-dimensional target electromagnetic scattering, a calculator mode about Finite Element-Boundary Integral(FE-BI) was set up to calculate the three-dimensional target electromagnetic scattering. Firstly, the three-dimensional target electromagnetic scattering calculation borderline integral was analyzed, and the vector Green function was introduced. On the basis of the connection between electromagnetism form and three-dimensional cavity form, the three-dimensional hatch cavity borderline mode was set up. Then, the finite element commonly function was established by combining the optical target surface modeling method with the higher order function method, and the application of the FE-BI to calculating three-dimensional target electromagnetic scattering was achieved. Finally, the following example analysis was proved. It is shown that the angle tally is very ideal when the dimensional bosom is empty or anisotropic matter. The consistance has been 90% as compared with the traditional matching method. In conclusion, the veracity and validity of calculation are improved by the proposed method.
Data processing of on-orbit spectral calibration of space-borne high resolution imaging spectrometer
2011, 4(2): 175-181.
Abstract:
In order to improve the spectral calibration precision of a High Resolution Imaging Spectrometer(HRIS) and to reduce the influence of the spectral shift on the surface reflectance retrieving of the ground spectra, especially in those wavelengths mostly affected by gaseous absorptions, the common data processing algorithms used in the on-orbit spectral calibration are introduced. The feasibility of these different algorithms is verified and their advantages and disadvantages are emulated with two cases of the laboratory spectral calibration under a thermal vacuum environment. It is shown that the algorithm based on spectra-matching, such as standard deviation method, correlation coefficient method and the minimized difference method can offer an advantage in the processing precision, and the extreme value method based on polynomial-fitting works much better in the processing speed. If polynomial-fitting method confirms the spectral shift fleetly in the pretreatment phase firstly, the spectral bound for spectral matching processing will be narrowed. A new algorithm with high processing precision and fast processing speed which combines spectra-matching and polynomial-fitting ideas was presented, it can offer the band-center wavelength accuracy better than 1 nm and can meet the need of the on-orbit spectral calibration precision of the HRIS.
In order to improve the spectral calibration precision of a High Resolution Imaging Spectrometer(HRIS) and to reduce the influence of the spectral shift on the surface reflectance retrieving of the ground spectra, especially in those wavelengths mostly affected by gaseous absorptions, the common data processing algorithms used in the on-orbit spectral calibration are introduced. The feasibility of these different algorithms is verified and their advantages and disadvantages are emulated with two cases of the laboratory spectral calibration under a thermal vacuum environment. It is shown that the algorithm based on spectra-matching, such as standard deviation method, correlation coefficient method and the minimized difference method can offer an advantage in the processing precision, and the extreme value method based on polynomial-fitting works much better in the processing speed. If polynomial-fitting method confirms the spectral shift fleetly in the pretreatment phase firstly, the spectral bound for spectral matching processing will be narrowed. A new algorithm with high processing precision and fast processing speed which combines spectra-matching and polynomial-fitting ideas was presented, it can offer the band-center wavelength accuracy better than 1 nm and can meet the need of the on-orbit spectral calibration precision of the HRIS.
2011, 4(2): 182-187.
Abstract:
In order to acquire a palmprint sampling image with high resolution, high contrast and low distortion and to achieve system lightweight and high performance-to-price ratio, a double telecentric optical system with 6 resin lenses was designed based on the principle of total reflection. The weight of system has been reduced largely due to resin lenses; and the resolution of acquired image has been enhanced because of the optical design based on the total reflection. Furthermore, the selection of the double telecentric optical system ensures the correction of the trapezoidal distortion introduced by the tilt object surface. It is shown that the Modulation Transfer Function(MTF) of the palmprint image sampling system is higher than 0.55 at Nyquist frequency of 228 lp/mm, and the maximum distortion of the image is less than 0.14%. Moreover, the collection range of system is 120 mm160 mm within a palm, the actual resolution of palm can reach 500 dots per inch, and the image resolution is 8106 pixels. These results meet the requirements of palmprint image sampling with high-precision and low distortion.
In order to acquire a palmprint sampling image with high resolution, high contrast and low distortion and to achieve system lightweight and high performance-to-price ratio, a double telecentric optical system with 6 resin lenses was designed based on the principle of total reflection. The weight of system has been reduced largely due to resin lenses; and the resolution of acquired image has been enhanced because of the optical design based on the total reflection. Furthermore, the selection of the double telecentric optical system ensures the correction of the trapezoidal distortion introduced by the tilt object surface. It is shown that the Modulation Transfer Function(MTF) of the palmprint image sampling system is higher than 0.55 at Nyquist frequency of 228 lp/mm, and the maximum distortion of the image is less than 0.14%. Moreover, the collection range of system is 120 mm160 mm within a palm, the actual resolution of palm can reach 500 dots per inch, and the image resolution is 8106 pixels. These results meet the requirements of palmprint image sampling with high-precision and low distortion.
2011, 4(2): 188-195.
Abstract:
Atomic Layer Deposition(ALD) was used to deposit TiO2/Al2O3 films at 110 ℃ and 280 ℃ on quartz and BK7 substrates in this paper. The microstructures of thin films were investigated by an X-ray duffractineter, and the Laser Induced Damage Threshold(LIDT) of samples was measured on a measuring table by a damage test system. Then, the damaged morphologies of the samples were investigated by an Atomic Force Microscope(AFM) and a Nomarski optical microscope, respectively. The results indicate that the films deposited by ALD show better uniformity and transmission, and its uniformity is better than 99% for a Ф50 mm sample and transmission is more than 99.8% at 1 064 nm. Furthermore, the LIDTs of the TiO2/Al2O3 films are (6.730.47) J/cm2 and (6.50.46) J/cm2 at 110 ℃ on quartz and BK7 substrates, respectively, which is notably better than that at 280 ℃.
Atomic Layer Deposition(ALD) was used to deposit TiO2/Al2O3 films at 110 ℃ and 280 ℃ on quartz and BK7 substrates in this paper. The microstructures of thin films were investigated by an X-ray duffractineter, and the Laser Induced Damage Threshold(LIDT) of samples was measured on a measuring table by a damage test system. Then, the damaged morphologies of the samples were investigated by an Atomic Force Microscope(AFM) and a Nomarski optical microscope, respectively. The results indicate that the films deposited by ALD show better uniformity and transmission, and its uniformity is better than 99% for a Ф50 mm sample and transmission is more than 99.8% at 1 064 nm. Furthermore, the LIDTs of the TiO2/Al2O3 films are (6.730.47) J/cm2 and (6.50.46) J/cm2 at 110 ℃ on quartz and BK7 substrates, respectively, which is notably better than that at 280 ℃.
2011, 4(2): 196-200.
Abstract:
According to the requirements of a three-dimensional laparoscope consisting of many group lenses for the high transmittance and distortionless imaging, the appropriate film materials were chosen. Then, a coating design softwave was taken to realize the nonperiod coating system design of the anti-reflective coating by using the vacuum evaporation method and an ion assistant deposition system. By adjusting parameters of coating film and using the technique of optical control and crystal control simultaneously, the thick control error was reduced and the anti-reflection coating was coated on the lenses that were used in the laparoscopy successfully. The test results demonstrate that the average reflectance of the preparated coating is less than 0.5% and it shows color distortionless, securely layers and better effects of resistant to corrosion. These results meet operating requirements of medical optical instruments.
According to the requirements of a three-dimensional laparoscope consisting of many group lenses for the high transmittance and distortionless imaging, the appropriate film materials were chosen. Then, a coating design softwave was taken to realize the nonperiod coating system design of the anti-reflective coating by using the vacuum evaporation method and an ion assistant deposition system. By adjusting parameters of coating film and using the technique of optical control and crystal control simultaneously, the thick control error was reduced and the anti-reflection coating was coated on the lenses that were used in the laparoscopy successfully. The test results demonstrate that the average reflectance of the preparated coating is less than 0.5% and it shows color distortionless, securely layers and better effects of resistant to corrosion. These results meet operating requirements of medical optical instruments.
