2010 Vol. 3, No. 6
Recent development status of space optical remote sensors in both earth and space detection fields is described. The specifications of several kinds of high resolution commercial satellites are given and the working properties of space telescopes on orbits and launching are summarized. Then, the developing trends of the high performance optical sensors with high resolution, wider fields of view and higher imaging quality are presented. According to the modeling of the large optical imaging platforms and the incorporating of earth and space optical sensors, it demonstrates the feasibility of intelligent optical imaging sensors based on the automatic target recognition and automatic parameter adjustment and gives working environments and technological demands of the sensors. Finally, it proposes the key techniques of space optical remote sensors in future, such as large aperture mirrors, active optical wavefront sensing and intelligent data processing on orbits.
The radiation environment is one of the reasons for the invalidation of CCD remote sensing cameras. In order to improve reliability of the cameras, anti-radiation techniques for electronic devices in CCD cameras were researched. The space radiation enviroment was introduced, then it points out that the solar activity, cosmic ray, Van Allent Belt and the secondary radiation are main sources of the radiation damage. Based on the study of space radiation environment, the radiation damage especially caused by Total Ionizing Dose(TID), Single Event Effect(SEE) and Displacement Damage(DD) on the electronic devices and integrated circuits was analyzed, respectively. Focused on the CCD camera, the anti-radiation tactics were proposed for CCD devices, integrated circuits and FPGA aspects. In the end, validating experiments for anti-radiation TID and anti-radiation SEE were carried out. Results demonstrate that this research provides some methods to increase the anti-radiation ability and improve the reliability of CCD remote sensing cameras.
The concept of space situation awareness is introduced and the present situations of photoelectric detecting systems on earth, in space and near space platforms are described. Then the performance and the characteristics of photoelectric detecting systems on earth, in space and near space platforms are analyzed. Analysis results indicate that the image quality of photoelectric detecting system on earth platform is limited by the atmospheric turbulence and atmospheric absorption, and most turbulence occurs in the troposphere and the lowest section of atmosphere. The photoelectric detecting system on the space platform can not be effected by atmospheric turbulence, but its detecting time is only 1/3 that of the ground telescopy. However, the photoelectric detecting system on the near space platform can not be disturbed by atmospheric troposphere, and its angular resolution could be greatly improved. On the basis of the advantages of the near space platform, the feasibility of developing the detecting system on near space platform is reviewed and the key technologies of the photoelectric detecting system based on the near space platform including materials, control technology, energy sources and high-energy physics are summarized in detail.
All materials have strong absorptin properties in Extreme Ultra Violet(EUV) region. Therefore, it is an only approach to construct a normal incidence optical system by using multilayer coatings to improve its reflectivity. In this paper, the development of EUV multilayer coatings is introduced and the key technologies for fabricating multilayer coatings(magnetron sputtering, electron beam evaporating, ion beam sputtering) and their relative apparatus are described. As multilayer coating reflective optical elements are mainly used in the EUV lithography and EUV astrophysics, it lays the emphasis on the study on the characteristics of multilayer coatings in EUV lithographic equipment, and the surface accuracy and thermal stability in coating processing. Furthermore, it also gives the special multilayer coatings for astronomical observations and discusses the fabrication of multilayer coating gratings and several problems to be solved.
A method for measuring the second-order diffraction efficiency of a grating in the vacuum ultraviolet region is introduced on the basis of the theory that the sample reflectance is influenced by the second-order diffraction efficiency of the grating. The measuring instrument by using a double path monochromator is also described, which takes a deuterium lap as the light source, a R6095 photomultiplier as the detector, and transforms the violet light into a visible light by a sodium salicylate scintillator film. By using the instrument, the second-order diffraction efficiency of the grating is measured from 120 to 165 nm continuously. Obtained results show that the second-order diffraction efficiency at 161 nm is 0.006 11(10.077 7), and the uncertainty of the system is 14.08%.
The performance of a hyper spectral imager is affected severely by the turbulence of orbit temperature, which would result in the thermal elastic deformation for the fore reflective telescope in the imager. Moreover, the thermal elastic deformation of mirrors, mechanical structure of the telescope, and the resulting displacements of the mirrors would induce defocusing. Based on the present study for a type of space hyper spectral imager, a model for simulating the thermal elastic deformation of the frontal telescope was built via Finite Element Method. By simulating, the surface deviation amounts and displacements of all the mirrors under different temperature loads were worked out, and the correlation between defocusing magnitude and temperature was obtained through calculating the resulting displacements of the mirrors. The analyzing results could be used as a reference for designing thermal controlling strategy and focusing system and for doing thermal-optical experiments of the developing imager.
The support structure of the combined dispersing prisms used in a hyper-spectrum imager is introduced, and the influence of the temperature changing on the image quality is discussed. The material of the clamping support is chosen according to the requirments, and the deformation of prism assemblies is simulated with the Finite Element Method(FEM) at the temperature differences of 5 ℃ to 10 ℃. It resolves emphatically the deformation of a prism reflector caused by the different linear expansion coefficients and analyzes the effect of the thicknesses and contact areas of the gaskets on the surface profiles of prism assembiles after the PTEE gaskets are used as a temperature compensation. Experimental results show that the surface profile of the quartz prism meets the requirement of /6 when the gaskets are added between the clamping support and the prism. The optimal result provides a reference for the support structure design of the combined dispersing prism.
The measuring precision of an electro-optical theodolite will fall down when the target moves relatively the measuring device. Moreover, the precision falling is more dependent on the speed of the relative movement. To improve the measuring precision of the electro-optical theodolite, this paper researches the reasons of above phenomena based on the TV exposure principle and proposes a new method to improve the data processing accuracy. The data matching algorithm based on the target missing and encoder position is proved in a simulation, and its feasibility for operating is also analyzed. The experimental results show that the algorithm can improve the measuring precision of the electro-optical theodolite by 20%~30%, which means that the measuring precision improves from 1/2 to 1/3 pixel of CCD.
A compact digital X-ray imaging system which adopts an X-ray sensitive CCD as an imaging detector was introduced for the dental imaging. A tooth model and a resolution testing card were used to test the revolution and radiographic dosage, respectively, and the subsection linearity correction was used to calibrate the nonuniformity of coupling of CCD and switch screen. In order to identify the bad pixel, a linear correlation coefficient was calculated to avoid the misjudgement. The imaging system was applied to an X-ray detection required a high resolution and a small work-area and the results show that the resolution of imaging system is higher than 10 lp/mm, radiographic dosage is less than 10% in contrast with that of X-ray film, and the calibrated nonuniformity of image has reduced by 27.5%. Obtained results prove that the system can satisfy the system requirements of high-revolution, low- radiographic dosage, and has a strong applied potential in X-ray detection for small objects.
The principle and requirements of the optical mount of an Extreme Ultraviolet Lithography(EUVL) system are introduced, and the mount structures according with the kinematic coupling requirements used in an actual lithographic camera and used in an interferometer are analyzed. The mount performance and key problems in mount precept are studied, and the corresponding solutions are also brought forward. Finally, Finite Element Analysis(FEA) models for optical mounts are built up, and the figure changes in the gravitation field and thermal field are analyzed, respectively. The results indicate that the figures on the mount structures used in the camera and used in the interferometer are the same basically in gravitational field, and the difference of the figure is 0.002 6 nm(RMS). When the temperature has a change of 0.05 ℃, the figure change of the structure is in the scale of 0.001 nm(RMS). The results show that the proposed kinematic mount structures can satisfy the mechanical requirements of mounts for EUVL systems.
Existing phase extraction algorithms are just insensitive to some specifically error sources, which can't satisfy the requirements of optical testing for the high precision. An equal-phase interval multi-step phase-shifting algorithm, weighted least square algorithm with underdetermined weight, was introduced. By introducing undetermined weights to the least square algorithm and by analysing the effect of manifold error sources on the algorithm in phase-shifting point diffraction interferometer, several groups of bound equations were obtained and the undetermined weights and the new phase extraction algorithm were determined by solving these bound equations. The new phase extraction algorithm was compared with standard four-step algorithm and Hariharan five-step algorithm. The results illuminate that the new phase extraction algorithm is much more insensitive to the linearity and nonlinearity of second order of PZT, intensity fluctuation in linearity and nonlinearity of 2nd order, linearity and nonlinearity of 2nd order of frequency of light source fluctuation. The results also illunimate that the new algorithm have advantages over other two algorithms in eliminating the CCD quantization, intensity noise, and the frequency noise. Moreover, the new algorithm is insensitive to the CCD nonlinearity at all.
To simulate the testing procedure of a Phase Shifting Point Diffraction Interferometer(PSPDI), the working principle of the PSPDI was introduced and its measuring errors were analyzed. On the basis of the lens design software and a inhome software, a test model for the PSPDI was established. By using the test model, the complex amplitudes of the reference beam and test beam were captured in an interference field, furthermore, the testing procedure was simulated. Depending on the optical coherent theory, the phase shifting was realized by changing the positions of testing mirror, and the phase shifting interferograms were acquired. Finally, for a given mirror, the model was used to generate two groups of 13-step phase intergrams with a symmetrical tilt. After processing the interferograms, it is shown that the accuracies of testing spherical mirror are 0.0783 nm(RMS) and 0.5656 nm(PV).
In order to characterize the structure of a Mo/Si multilayer, the Small Angle X-ray Diffraction(SAXD) of a multilayer sample is measured and the analytical methods of SAXD data were introduced, including Bragg peak fitting, Fourier transform, and X-ray diffraction fitting. The period thickness of the multilayer obtained by the Bragg peak fitting or X-ray diffraction curve fitting is 7.09 nm. The interface roughness(interdiffusion length) are 0.40-0.41 nm(Si on Mo) and 0.52-0.70 nm(Mo on Si), respectively. And the former is smaller than latter, which is consistent with the Transmisson Electron Microscopy(TEM) results in 0.40 nm(Si on Mo) and 0.6-0.65 nm(Mo on Si). Meanwhile, the refractive profile extracted by the X-ray diffraction fitting with a diffusion model is also consistent with the gray-scale profile by integrated High Resolution TEM(HRTEM). By the comprehensive characterization of the X-ray diffractometry(XRD) and TEM, the fine structural information of the Mo/Si multilayer is obtained, which is critical for the technology optimization of the multilayer deposition.
HfO2 thin film is one of the most important films for optical applications in ultraviolet optics. As different fabrication methods will result in the different properties, it is essential to choose appropriate fabrication methods for practical applications. In this paper, HfO2 thin film for ultraviolet optics was fabricated by e-beam evaporation and ion beam sputtering, respectively. The material and optical properties of HfO2 thin film were measured and compared. The refractive index n and extinction coefficients k of HfO2 thin films were obtained by numerically fitting the measured transmittance and reflectance curves in the wavelength of 230-800 nm. Obtained results indicate that both the extinction coefficients from e-beam evaporation and ion beam sputtering are less than 210-3. On the basis of above works, two kinds of typical ultraviolet optics, violet low pass filter and 240 nm high reflector, were fabricated by e-beam evaporation and ion beam sputtering, respectively, and both of the devices have high spectral properties.
On the basis of the brightness definition of Vertical-cavity Surface-emitting Lasers(VCSELs), the brightness characteristics of high power strained quantum well 980 nm InGaAs/GaAs VCSEL with a diameter of 400 m are demonstrated at continuous-wave(CW) operation with a recycled water cooling(the temperature is controlled at 15 ℃). The results show that when the injection current is smaller than 4 A, the brightness will increase with the increasing of injection current; while the injection current is larger than 4 A, the output power increases with the increasing of injection current, but the beam quality becomes bad, and then the M2 is the main factor impacting on the brightness characteristics. When the injection current is 4 A and the output power is 1.2 W, the beam quality is the best, M2 factor achieves 207, and the maximum brightness is 2.43 kW/cm2sr. Finally, the main factors that impact the brightness characteristics of high-power VCSEL devices are analyzed, and the solutions to improve the brightness characteristics of the device are also proposed.
The support system of a one-meter primary mirror was optimally designed by the finite element method. For the analysis, the 3D solid finite element model was estabilished by the finite element software. Two kinds of lateral support structures were compared, then the axial support-ring radius, lateral support form and the lateral support position were determined after the optimum design. The mirror deformations with different pitching angles were calculated, and the maximum Root-mean-square(RMS) value of the surface deformation is 5.3 nm. Obtained results satisfy the design requirement and show that the support system is reasonable and feasible. This optimal method of finite element and calculated process are independence on the diameter and thickness of the primary mirror, and are also useful for the designs of primary mirrors in the planar form, spherical form and allotype form.
A mechanism structure for the focal output of a zoom lens in varifocusing process was designed based on the relation of system focus, variable magnification unit and compensation unit in the optical design. A line displacement sensor was taken as feedback, a worm wheel and a worm as drive-elements in the mechanism structure, and a joint pole was adopted to fix and join the high-precision line displacement sensor and the zoom lens, so that the motion values of zoom lens was directly feeded back to the voltage of line displacement sensor. As compared with traditional mechanism structure that the focal-length was calculated by the relation of the cam rotational angle acquired by gear-driven potentiometer, the precision was low for the last motion error of gear, clearance of cam, drive nail and the potentiometer error. The results of precision analysis show that the focal-length can be obtained immediately based on the voltage of line displacement sensor which reflectes the displaces of zoom lens, therefore the precision for focal output is improved greatly.
In order to meet the requirements of offshore calibration for theodolites and to reduce calibration costs, this paper presents a calibration method of shipborne theodolites. Using this method, almost all the work can be carried out at sea. At first, based on FK5 ephemeris, the apparent position of a star can be calculated in real-time. After the coordinate transition, bootstrap values in the measurement system are ready. The algorithm of ship movement is used to keep the stablization of tracking at sea. At the same time, real-time data are acquired and recorded, and the axis errors and system errors of the theodolite can be calculated based on several algorithms. Experimental results indicate that the precisions of the calibration in dry-dock and the star calibration are very close. The tolerances of visual axis error, horizontal axis error and the vertical axis error are 0.015, 0.22 and 0.014, respectively. The star calibration agrees with the former results very well in system errors after calculations. It can satisfy the requirements of offshore calibrating of a ship-based theodolite.
In order to analysis the influences of environment radiation and atmosphere absorbing on the measurement precision, the infrared temperature measurement by using a middle-wavelength infrared detector is studied. Firstly, several environment radiations which influence the measurement precision of a middle-wave Infrared Focal Plane Array(IRFPA) are introduced, and the relation between the gray and the absorbed radiation of the infrared detector is deduced. Then the amending formulae of environment radiations are achieved. Using the blackbody as the measurement target, the measurement error are 3.56 ℃ and 0.27 ℃ before and after amendings, respectively, and the measurement precision is improved evidently. The results show that the amending formulae could modify the influences of environment radiation and atmosphere absorbing correctly.
This paper introduces the concept of stray radiation and its influence on the image quality of a optical system. By taking a refractive infrared optical system as an example, it simplifies the 3D optical-mechanical system properly and uses the Monte-Carlo model built-in Light tools to analyze the stray radiation of the system and to obtain the illuminance distribution of image in the system. Meanwhile, it calculates the radiation of surfaces in different parts of the system, and compares their influences on the image quality of the system. Furthermore, it points out that the inter surface of fore frame in the proposed system is a main source of stray radiation. Corresponding to the results, this paper finally investigates the restraint ways for the stray radiation, which can be a reference for the following designs.
On the basis of the demands of high resolution in imaging technologies of developing engineering practices, the imaging principles of an optical synthetic aperture and the advantages in improving the resolution of image was discussed in this paper. The domestic and foreign research results and the exciting technical difficulties in the relevant research fields also were demonstrated. In the current conditions of processing and testing alignment, the imaging experiment of two sub-aperture telescope was designed. From theory of geometrical optics, using Fizeau-type multi-aperture telescope, the experimental possibility of Fizeau-type synthetic aperture was investigated. The adjustment accuracy of the key components in the synthetic imaging system was researched, which ensures that the system can make an image completely. In the experiments, the fine tuning mechanism with a designed resolution less than 0.03 mm ensures that the system can obtain a clear image, and the precision piezoelectric linear drive system with a resolution 0.05 m guarantees the synchronization of two beams' phases. The results show that the foundation of the designed experiment is feasible, and the system can offer the exact resolution values. This research makes a useful basis for the synthetic aperture imaging system, and has important potential in practices.
The vectorial diffraction numeric algorithm, Rigorous Coupled Wave Analysis(RCWA), was introduced, and it was used to calculate the diffraction efficiency of a subwavelength blazed grating precisely and to investigate the diffraction characteristics. Firstly, the electromagnetic medium model was created, and the irregular structure was simplified into a multi-layer rectangle grating. The rigorous coupled wave equation among the electromagnetic field was built, and the electromagnetic distribution based on the boundary conditions was solved. After that, enhanced transmittance matrix approach was employed to iterate the results between layers, and finally the diffraction efficiency of the whole structure was solved. Calculated results show that the diffraction efficiency of aluminium film grating with the blazed angle of 11.3 and a period of 500 nm is higher than 90% and can also offer a relative blazed order. This numerical vectorial diffraction algorithm has a good precision and wider applications in the calculation of the high and compact complicated grating.