Wigner function-based modeling and propagation of partially coherent light in optical systems with scattering surfaces.

The primary mirror component is an important part of the Cassegrain system. As the first-stage imaging component, the RMS surface error directly affects the image quality of the whole optical system. In this article, taking the primary mirror component of a certain type of Cassegrain aerial camera as the research object, the factors affecting the RMS precision of the primary mirror surface are analyzed in detail from aspects of back supporting structure design, platen elastic crimping design, simulation analysis, test verification and so on. Using the finite element method to simulate the primary mirror supporting structure, analyzes the influence on the primary surface error by the three-point supporting structure in different positions. Furthermore, analyzes the variations of the primary mirror surface error under the influence of three-point supporting structure and pressure plate. The last but not the least, analyzes the primary mirror surface error under the different pressure conditions, concludes the optimal supporting point position and the excellent elastic compression. After the primary mirror assembling, through test verification, the RMS is 0.0270λ, which is better than the original design requirement of λ/35(0.0286λ). And the RMS variation between before and after assembling is less than 0.005λ. Performing the high and low temperature test on the primary component, after test, the RMS values is 0.0269λ, it proves that the primary frame structure and its axial supporting structure have little effects on the RMS precision of the primary mirror. It can also meet the requirement of the large-aperture primary mirror surface in the co-optical system under complex conditions. The feasibility of the structure design has been verified.

In order to improve the imaging quality of optical system, high precision surface of mirrors are put forward to improve their imaging quality. It makes their fabrication harder. Wavefront aberration induced by alignment is analyzed in off-axis parabolic mirror system based on the wavefront aberration theory. The surface error of off-axis parabolic mirror can be compensated by alignment so it will reduce the fabrication difficulty, shorten its period and save its cost. In the simulations of an off-axis parabolic mirror with surface error λ/40 RMS (λ=632.8 nm) ( Root Mean Squre) with ZEMAX software, the figure accuracy is under λ/40 RMS after alignment. It shows that surface error of off-axis parabolic mirrors could be compensated effectively by alignment.

A statistical simulation model for positional error of line features in Geographic Information Systems (GIS)

An objective method has been developed for measuring the stray light in optical systems. Stray light reduces the contrast of image and falsely appears to augment the light transmission of optical system. The method utilizes a photoelectric apparatus to compare the contrast of an image formed by an optical system with the contrast of the object under examination. This comparison, when expressed on a percentage basis, is referred to as “the contrast rendition” of the optical system. The contrast rendition of telescopic, photographic, and microscopic systems has been studied under a variety of conditions. It has been found that the contrast rendition values range from 3 to 100 percent for the systems studied. The contrast rendition of an optical system has been found to depend upon its optical and mechanical design, the use of reflection reducing films, surface defects, the cleanliness of its optical surfaces, the use of lens shades, and the brightness condition of the region surrounding the object under examination. The contrast rendition, for large targets and for a uniform surround, has been found to be independent of the brightness level at which the measurements are made, the contrast of the object, the field angle, and the optical aberrations present in the systems examined. The importance of contrast rendition in telescopic systems has been evaluated using the methods and data of Hardy, Duntley, and Blackwell. This evaluation was made by comparing the computed loss in range that would be caused by an imperfection in contrast rendition with the loss caused by an equal imperfection in light transmission and in magnification for telescopic systems. It was found, for all brightness levels, that the contrast rendition was generally more important than the other two variables. Because of the indicated strong dependence of the range at which targets are visible upon contrast rendition, ranges were computed for specific objects, instruments, and observation conditions, and compared with the results of an extensive visibility field test conducted from aboard ship. The computed and observed ranges were found to be in close agreement. This indicates that the contrast rendition of an optical system is a major factor in determining its performance.

A new error modelling and identification method based on the cross grid encoder is proposed in this paper. Generally, there are 21 error components in the geometric error of the 3 axis NC machine tools. However according our theoretical analysis, the squareness error among different guide ways affects not only the translation error component, but also the rotational ones. Therefore, a revised synthetic error model is developed. And the mapping relationship between the error component and radial motion error of round workpiece manufactured on the NC machine tools are deduced. This mapping relationship shows that the radial error of circular motion is the comprehensive function result of all the error components of link, worktable, sliding table and main spindle block. Aiming to overcome the solution singularity shortcoming of traditional error component identification method, a new multi-step identification method of error component by using the Cross Grid Encoder measurement technology is proposed based on the kinematic error model of NC machine tool. Firstly, the 12 translational error components of the NC machine tool are measured and identified by using the least square method (LSM) when the NC machine tools go linear motion in the three orthogonal planes: XOY plane, XOZ plane and YOZ plane. Secondly, the circular error tracks are measured when the NC machine tools go circular motion in the same above orthogonal planes by using the cross grid encoder Heidenhain KGM 182. Therefore 9 rotational errors can be identified by using LSM. Finally the experimental validation of the above modelling theory and identification method is carried out in the 3 axis CNC vertical machining centre Cincinnati 750 Arrow. The entire 21 error components have been successfully measured out by the above method. Research shows the multi-step modelling and identification method is very suitable for ‘on machine measurement’.

The control of surface errors as a function of spatial frequency is critical during the fabrication of modern optical systems. A large-scale surface figure error is controlled by a guided removal process, such as computer-controlled optical surfacing. Smaller-scale surface errors are controlled by polishing process parameters. Surface errors of only a few millimeters may degrade the performance of an optical system, causing background noise from scattered light and reducing imaging contrast for large optical systems. Conventionally, the microsurface roughness is often given by the root mean square at a high spatial frequency range, with errors within a 0.5×0.5 mm local surface map with 500×500 pixels. This surface specification is not adequate to fully describe the characteristics for advanced optical systems. The process for controlling and minimizing mid- to high-spatial frequency surface errors with periods of up to ∼2-3 mm was investigated for many optical fabrication conditions using the measured surface power spectral density (PSD) of a finished Zerodur optical surface. Then, the surface PSD was systematically related to various fabrication process parameters, such as the grinding methods, polishing interface materials, and polishing compounds. The retraceable experimental polishing conditions and processes used to produce an optimal optical surface PSD are presented.

Apodization of pupil with various amplitude filters have been investigated for altering the point spread function for diffraction-limited optical systems' pictures of point objects by employing various filters, such as connes and tringle filters. We have shown that, for different levels of amplitude apodization, the lower values. An observation that these filters give good results for lower values of the apodization parameter. (FWHM) Full width at half maximum of the point spread function (PSF) is smaller than the Airy PSF, improving the performance of the optical system.

On the basis of optical correlation detection, photoelectric hybrid joint transform correlator(JTC) is widely used in military, aviation and intelligentization, etc. It has the advantages of great flexibility and high precision of recognition. However, the optical system which is in front of joint transform correlator(JTC) is applied to receive the infrared radiation of the target. It also has a certain influence on JTC’s detecting precision and tracking ability. Dual band infrared imaging system can receive different wave band of infrared radiation. Therefore, the image quality of optical system plays an important role in the joint transform correlator(JTC). According to the requirements of the joint transform correlator (JTC), the processes of optical design including the allocation of parameters and the selection of initial structure are presented. The infrared dual band coaxial telephoto system is designed for target detection. The system which is composed of four lenses can image in both 3μm~5μm and 8μm~12μm wavebands. The focal length is 200 mm and the relative aperture is 1:3. The system has the characteristics of small volume and compact structure. The optical system image quality is evaluated with ZEMAX optical design software. The results have shown that MTFs of the system are 0.62 and 0.35 for both wavebands respectively at 17lp/mm of spatial frequency which are closed to the diffraction limited curve. The relative aperture, field of view, and focal length are same for both spectral regions. The system meets the requirements of technical specification and improves the ability of JTC in target tracking and recognition.

The relationship between image quality and piston errors of synthetical aperture optical imaging system has been studied. An active segmented cophasing imaging system and its Zemax simulation model were set up. Diversity piston errors were introduced and the corresponding MTF were calculated with the Zemax simulation model. Simulation experiments have been carried out with the cophasing imaging system, and the results are coincident with the simulated results. The results show that image quality changes with the increase of the piston error periodically if the piston error is smaller than the coherent length of the light source, and the image quality becomes the worst if the piston error is an odd multiple of π.

For the space solar extreme ultraviolet telescope, the star point test can not be performed in the x-ray band (19.5nm band) as there is not light source of bright enough. In this paper, the point spread function of the optical system is calculated to evaluate the imaging performance of the telescope system. Combined with the actual processing surface error, such as small grinding head processing and magnetorheological processing, the optical design software Zemax and data analysis software Matlab are used to directly calculate the system point spread function of the space solar extreme ultraviolet telescope. Matlab codes are programmed to generate the required surface error grid data. These surface error data is loaded to the specified surface of the telescope system by using the communication technique of DDE (Dynamic Data Exchange), which is used to connect Zemax and Matlab. As the different processing methods will lead to surface error with different size, distribution and spatial frequency, the impact of imaging is also different. Therefore, the characteristics of the surface error of different machining methods are studied. Combining with its position in the optical system and simulation its influence on the image quality, it is of great significance to reasonably choose the processing technology. Additionally, we have also analyzed the relationship between the surface error and the image quality evaluation. In order to ensure the final processing of the mirror to meet the requirements of the image quality, we should choose one or several methods to evaluate the surface error according to the different spatial frequency characteristics of the surface error.

A recent study of the influence of the Goos-Hänchen shift on the imaging properties of planar optical systems is commented on. It is shown that the model chosen for a description of the Goos-Hänchen shift must be modified considerably and that there is one more shift in total reflection that will also influence the imaging quality.

The design of optical systems not only considers the imaging performance but also the manufacturing difficulty and feasibility of the system. In practice, errors in the manufacturing process of glass materials and deviations in glass material parameters introduced in complex environments can both lead to degradation in the imaging quality of optical systems. Optical systems that are sensitive to glass material errors face increased manufacturing difficulty and reduced stability. This paper, based on geometrical optics theory, establishes an evaluation function for refractive index error sensitivity and analyzes its relationship with optical parameters and glass materials. It proposes a design method to reduce the refractive index sensitivity of optical systems. Through simulation verification and analysis using examples, the validity of the desensitization design method is confirmed.

Taking a certain type of photoelectric system of armored vehicle as an example, the influence of angular vibration on the optical system image quality is analyzed. Firstly, the paper introduces the characteristics of photovoltaic system and the basic theory of imaging; Then it uses the ZEMAX to build optical system model; finally, it simulates the MTF and Spot Diagram as the change of lens angular. By making quantitative analysis of the photoelectric system influence on imaging quality of lens deflection angular, we get the relationship between geometry maximum radius and mean root square radius with the lens deflection angular, and evaluate the effects of angular vibration on image quality synthetically, which has important reference value to the design of photoelectric system.

Electronic nose simulation tool centred on PSpice

The graded-index (GRIN) media have been widely used in modern optical systems, such as imaging lenses, optical beam delivery components, and beam shaping elements. Accurate and efficient modeling of electromagnetic fields propagating in GRIN media is essential for developing innovative and high-quality optical products. It is the goal of this thesis. We first give an overview of several existing modeling techniques, including the rigorous ones to model symmetric GRIN structures, e.g., Mie theory (spherically symmetric) and several beam propagation methods (BPMs) with approxiamations to model general GRIN structures, which are numerically more efficient than rigorous methods. However, many of BPMs are limited by considering only a small variance of the refractive index. To overcome the limitations, we develop a unified field solver, known as the Runge-Kutta (RK) k-domain field propagation method. It can be used to calculate general input fields propagating through an arbitrary GRIN medium, accurately, without physical approximations, such as the scalar field approximation or the paraxial approximation. We convert Maxwells equations in spatial (x-) domain into ordinary differential equations (ODEs) in the spatial-frequency (k-) domain, which can be solved iteratively using the RK method. In our numerical calculation, taking advantage of the convolution theorem, the total numerical effort is linear in the number of sampling points. As many GRIN components are modeled or designed using ray tracing techniques, the field passing through the GRIN components must show negligible diffraction, which satisfies the geometric field assumption. By substituting geometric field ansatz into the ODEs of RK k-domain field propagation method and Maxwells equations, we obtain two ODEs in x-domain. After solving them by using again RK method, the RK x-domain field propagation method is established.