In the inertial confinement fusion system (ICF), surface scratches of the large diameter optical surface appear as dot lines (punctate scratches). This kind of scratches is only detected under a high microscope magnification system. This can be caused by the blemishes on the optical processing technology and shallow scratches (< 25nm ). As a result, it can have an impact on the relevant calculation of the width and length of the scratches. Besides, this kind of scratches has a serious impact on the ICF, such as system damage. To solve this problem, this paper proposes the image pattern charter of punctate scratches based on the existing surface defects detection system (SDES). Finally, it proposes an algorithm of scratches based on the linearity differential detection and connectivity. That is, using coordinate transformation and direction differential-threshold discrimination, the scratches can be connected effectively and calculated exactly. Experimental results show that punctate scratches parts can be connected correctly, and the accuracy of the calculated length reaches 95%. Also, the improved algorithm applies to the arc-shaped scratches, which is based the block image processing. Currently, this algorithm can be applied to connect and calculate the shallow scratches accurately and precisely on large fine optics in the ICF system. Thus it can also decrease the misdetection rate of nonconforming super-smooth optics in the ICF system.
The high-resolution detecting system based on machine vision for defects on large aperture and super-smooth surface uses a novel ring telecentric lighting optical system detecting the defects on the sample all round and without blind spots. The scattering light induced by surface defects enters the adaptive and highly zoom microscopic scattering dark-field imaging system for defect detecting and then forms digital images. Sub-aperture microscopic scanning sampling and fast stitching on the surface is realized by using precise multi-axis shifting guided scanning system and a standard comparison board based upon binary optics is used to implement fast calibration of micron-dimension defects detected actually. The pattern recognition technology of digital image processing which can automatically output digitalized surface defects statements after scaling is established to comprehensively evaluate defects. This system which can reach micron-dimension defect resolution can achieve detections of large aperture components of 850 mm × 500 mm, solve the durable problem of subjective uncertainty brought in by human visual detection of defects and achieve quantitative detection of defects with machine vision.
Based on microscopic imaging and sub-aperture stitching technology, Surface defect detection system realizes the automatic quantitative detection of submicron defects on the macroscopic surface of optical components, and solves quality control problems of numerous large- aperture precision optical components in ICF (Inertial Confinement Fusion) system. In order to improve the testing efficiency and reduce the number of sub-aperture images, the large format CCD (charged-coupled device) camera is employed to expand the field of view of the system. Large format CCD cameras are usually mosaicked by multi-channel CCD chips, but the differences among the intensity-grayscale functions of different channels will lead to the obvious gray gap among different regions of image. It may cause the shortening and fracture of defects in the process of the image binarization , and thereby lead to the misjudgment of defects. This paper analyzes the different gray characteristics in unbalance images, establishes gray matrix mode of image pixels, and finally proposes a new method to correct the gray gap of CCD self-adaptively. Firstly, by solving the inflection point of the pixel level curve in the gray histogram of the original image, the background threshold is set, and then the background of the image is obtained; Secondly, pixels are sampled from the background and calculated to get the gray gap among different regions of the image; Ultimately, the gray gap is compensated. With this method, an experiment is carried out to adjust 96 dual-channel images from testing a fused silica sample with aperture 180mm×120mm. The results show that the gray gap of the images on different channel is reduced from 3.64 to 0.70 grayscale on average. This method can be also applied to other CCD mosaic camera.
The digital calibration method, which is employed in the Surface Defects Evaluation System (SDES) for the defects evaluation of large fine optical surfaces, is presented in this paper. A criterion board, which comes from special design and careful fabrication, is employed to relate the dimensions of the defects and those of their images. The calibration procedure, including collecting of calibration images, digital image processing and calibration function fitting, is described in detail in this paper. Calibration experiments on scratch width and dig diameter were carried out at three different microscope magnification conditions. Experiment results show that following the proposed digital calibration method, micron-sized defects distributed sparsely on a large-aperture fine optical surface can be evaluated with micron accuracy and high efficiency.
High spectral resolution lidars (HSRLs) have shown great advantages for the measurement of backscatter and extinction coefficients of aerosols and clouds due to its spectral discrimination process, which brings about more straightforward and accurate retrieval without additional assumptions in contrast to standard backscatter lidars. We have developed a tilted, field-widened Michelson interferometer (FWMI) to obtain this spectral discrimination. The interferometer is composed of a cubic beam splitter, a solid arm and an air-solid blending arm, and will be employed as the spectroscopic filter of an HSRL to block the aerosol signals but transmit the molecular backscattered photons optimally. In this paper, a comprehensive radiometric model is developed to evaluate the spectral discrimination performance of the FWMI, especially under varies of practical imperfections, such as fabrication errors and utility defections. The principle of the modeling for tilted FWMI as the spectroscopic filter of the HSRL has been presented, through which, the effects on transmittance characteristics of the FWMI from these practical imperfections are analyzed in detail. The model can be used to evaluate the machinery tolerance budgets for new FWMI designs and decide optimal state of usage for FWMI appliance.
High spectral resolution lidars (HSRLs) are becoming more and more important in profiling atmospheric aerosols as accurate measurement can be achieved by employing the high-spectral-resolution spectroscopic filter. A field-widened Michelson interferometer (FWMI) is specially designed to be the spectroscopic filter for a near-infrared HSRL. The FWMI is superior to other commonly used filters, such as F-P interferometric filters and atomic/molecular absorption filters for its large angular acceptance, high photon efficiency and wavelength flexibility. It consists of a cubic beam splitter and two orthogonal arms. In this paper, the designing procedure of determining the materials and dimensions of the arms is described in detail. The result designed to the spectral line of 1064nm is presented and is analyzed to have good working performance. A tolerance evaluation model is also established to assist the design process.
It is considered challenging to evaluate the sparse microdefects of large optical surfaces because the microdefects are
usually of microns while the test samples are of hundreds of millimeters. Most of the existing methods encounter
problems such as uncertainty and inefficiency in eyeballing, inconsequence between laser source and international
standard, limitation of detecting area, qualitative but not quantitative nor standard measurement of defects, etc. In this
paper, a dark-field microscopic scattering imaging system for microdefects evaluation is introduced. The principle of the
proposed surface microdefect evaluation system will be presented and the experiment results on evaluating numerous of
test samples will be given.
In large aperture component’s dark-field scattering defects imaging system, the component’s size is large and part with a
wedge. When the component is in the completely level position, the surface defects image can be clearly acquired by a
high magnification microscope. Otherwise, fuzzy defects image would be gained because of defocusing which makes
digital identification can’t be able to be done. For the problem of leveling large aperture, wedge component, this paper
proposes a method that using image information entropy as focusing evaluation function for leveling large aperture
components. Firstly, in three different points of component surface acquiring multi-images by the same continuous steps.
Then calculating the images’ entropy and fitting a curve to it. Based on minimum image information entropy value
criterion, the focal plane can be found and each point’s defocusingamount of the fist acquisition position can be gained.
Relay on the relation model of acquisition points, adjust points and defocusingamount that has been built, each adjust
point’s adjustment can be got. The component’s level position can be achieved by adjusting the adjust points. In the
experiment that using a high magnification (of 16) microscope scans over the whole surface of the component with the
size of 430mm×430mm. The image microscope is always in the depth of focus which shows that the leveling precision
has achieved 20μm. Until now, this method has been successfully used in large aperture component’s dark-field
scattering defects imaging system.
It is hard to quantitate the micron-scale defects on large aperture (102mm×102mm) optical components by the
conventional optical testing methods. This paper proposes a super-smooth surface defects measurement and evaluation
system, achieved by using microscopic dark-field scattering imaging device, two-dimensional sub-image scanning
mechanism and multi-cycle image mosaic algorithm. The defects detecting system, with a lateral resolution of 0.5μm,
applies a large field of view design (largest FOV: 15mm×15mm). In order to test the largest element (430mm×430mm),
however, over 1000 sub-pictures are captured. It takes more than 30 minutes to process these sub-pictures by multi-cycle
image mosaic algorithm. This paper also presents a distortion correction method to revise the image mosaic mismatch
caused by the optical distortion in the defects testing system on the platform of MATLAB. A binary optical grid plate
(BOE) is fabricated as standard board to evaluate distortion. The proposed method applies image division multi-steps to
build a look-up matrix of distortion parameters. According to the look-up matrix, all pixels on a sub-image are repositioned
from the distortion Cartesian coordinates to the ideal Cartesian coordinates. Finally, feasibility of the
distortion correction method is demonstrated by comparing the mosaic results of defect images before and after this
process. The full field view distortion is reduced from more than 4% to less than 0.1%. After distortion correction, subimages
can be directly mosaicked without using multi-cycle image mosaic algorithm, which improves test efficiency
significantly. The method mentioned in this paper may also apply to other optical testing systems for image mosaic.
A digital calibration method for defect dimension of the optical surface is put forward to get the correspondence between the actual scale of defect on optical surface and the number of pixels of the defect image captured by CCD. Standard scratches, with their width ranging from 0.5μm to 40μm, are fabricated by electron beam exposure and reactive ion beam etching on two kinds of standard calibration board, quartz calibration board with and without chromium film. Calibration experiments are accomplished in five different microscope magnifications. Threshold segmentation, morphological operation and feature extraction are carried out in the images of calibration board to obtain the width of standard scratches in pixels. Interpret the theoretic trend of the calibration function as well as the linear range of it, and fit the calibration function based on the experimental results. According to the analysis and comparing of the calibration results in different microscope magnifications, error source and the factors limiting the resolving accuracy of the calibration system are analyzed. Ultimately, a standardization process including fabrication of the standard scratch, establishment of the standard calibration library for different microscope magnifications and the rapid calibration of actual detect is established. The calibration of the defects on the optical element in the size of 450mm× 450mm is successfully realized.
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