光学外文文献及翻译

1、学号 2013211033昆明理工大学昆明理工大学专业英语专业英语专业光学姓名辜苏导师李重光教授分数导师签字日期2015 年 5 月 6 日研究生部专业英语考核专业英语考核年级：年级：2013 级学院：学院： 理学院姓名姓名：辜苏学号学号： 2013211033专业：专业：光学文献原文：Title：Phase-shifting digital holography in image reconstructionAbstract: A phase-shifting digital holography scheme developed to investigateinternal defects

2、 in artworks is described. Phase-shifting is utilized to obtain a clearreconstructed object wave from a rough surface texture. A reverse-transformalgorithm is employed to reconstruct the object wave on its original position ofunknown distance or the imaging position from the object wave information

3、on theholographic plane. To get the clearest reconstruction the exact registration of theunknown distance is determined by applying the intensity sum as the auto-focusingfunction. The spatial resolution of the reconstruction image is also investigated for avariety of affecting factors. Laboratory re

4、sults of reconstruction images underdeformation are presented.Key words：holographic interferometry, digital holography, phase-shifting technique,reverse-transform algorithm, auto-focusing function, spatial resolution.1 Introduction Different methods of holographic interferometry relatedtechniques ha

5、ve been used effectively for defect visualisation in artworkdiagnosis. Physical reconstruction of recorded wave fields though is of limitedapplicability for on-field or remote applications usually required in artconservation environments. Digital counterparts explored nowadays to recordthe interfere

6、nce between an object and its reference on CCD and reconstruct therecord numerically are better suited for field use. However they do not providethe essential spatial resolution for clean object reconstruction and defectdetection, both critical in artwork diagnostic assessment. Towards this goal, th

7、isstudy aims at overcoming the above limitations and expanding the use of suchtechniques in the field of artworks conservation.A principal problem in digital holography of artworks is to obtain a clearreconstruction. To accomplish this the following problems should be addressed:(1) need of a proper

8、algorithm for the reconstruction of recorded images, (2)removal or elimination of speckle noise in the reconstructed image and phasemap, (3) determination of the actual registration distance, (4) improvement ofspatial resolution of the reconstructed image.The first two problems is referred to as rec

9、onstruction algorithms. Thesealgorithms can be divided into two categories. One realizes reconstruction froma single hologram as for example the Fresnel algorithm and the convolutionalgorithm. Such algorithms only require a single hologram and are suitable fordynamic measurements, but the zero-order

10、 speckle and the effect of thereference beam are not thoroughly removed. The second combines thephase-shifting technique and digital holography together to produce imagereconstruction. Its important advantage is the ability to eliminate completely theeffect of the reference beam, so it can get a cle

11、ar reconstructed image. In digitalholography of artworks, most of the investigated objects have a coarse surfaceand big slope changing so that the spatial phase-shifting technique is unsuited.Therefore, even if the temporal phase-shifting technique is improper fordynamic testing, it is applied widel

12、y. In this approach, the first step uses aphase-shifting technique to record the object wave on the holographic plate.Then the reconstruction object wave can be calculated at its original or imagingposition. Towards this goal we propose a reconstruction algorithm based on areverse-transform algorith

13、m, which accords with the notion of the digitalholography in principle and also produces good reconstruction results.In the reconstruction process, if the registration distance used has a bigdifference with its actual value, the reconstructed image will be fuzzy. In a firstapproximation, this distan

14、ce can be measured in the optical testing system orestimated by the clarity obtained in the reconstructed image, but suchapproaches lack accuracy and standardization. This paper proposed a method todetermine the exact registration distance, which applies the intensity sum of thereconstruction image

15、as the evaluating function in order to determine the truevalue. Improving the reconstructionspatial resolution is an important problem worth addressing.2 Reconstruction based on phase-shifting digital holographyThe relationship between the object, hologram and reconstructed image isshown Fig.1, wher

16、e x and y denote the coordinates of the object plane,andthe hologram plane, andxandythe reconstruction plane,d is theregistration distance,dis the reconstruction distance.In digital holography, the recording CCD is placed on the-plane in ordertoregisterthehologramx,ywhen theobject lies inthex-yplane

17、.Forthereconstructionoftheinformationoftheobjectwave,phase-shifting digital holography includes two steps:(1) getting objectwave on hologram plane, and (2) reconstructing original object wave.2.1 Getting information of object wave on hologram plateDoing phase shifting N-1 times and capturing N holog

18、rams. Supposing theFig.1 Geometric coordinate of digital holographyinterferogram after k- 1 times phase-shifting is),(cos),(),(),(kkbaI（1）Phase detection can apply two kinds of algorithms:synchronous phase detectionalgorithms9and the least squares iterative algorithm10. The four-step algorithmin syn

19、chronous phase detection algorithm is in common use. The calculationequation is)2/3 ,(),()2/,()0 ,( 2/1),(iIIiIIE2.2 Reconstructing original object wave by reverse-transform algorithmObject wave from the original object spreads front.The processing has exactandcleardescriptionandexpressioninphysicsa

20、ndmathematics.Byphase-shifting technique, we have obtained information of the object wavespreading to a certain distance from the original object. Therefore, in order to getthe information of the object wave at its initial spreading position, what we needto do is a reverse work.Supposing the hologra

21、m registration satisfies Fresnel approximate condition,namelymax2223)()(4yxdthen the object wave on the hologram plane can be written asdxdyyxdiyxdikyxOdikdiikdOg)(2exp)(2exp),()(2exp)exp(),(2222（2）In this equation, the first term exp(ikd)/(id) is a constant and does not affectthe reconstruction res

22、ult, thus can be omitted. Digital Eq.(2) gives),(),(),(),(1lkwlkOFmnzmnOg)(2exp),(2222mndikmnz)(2exp),(2222ylxkdiklkwWhere N is the pixel number of CCD.So the original object wave is expressed as),(/),.(),(),(lkwmnzmnOFlkOgIn order to adjust the position of the reconstruction image, an adjusting fac

23、tor Ris added to),(/),.(),(),(),(lkwmnzmnRmnOFlkOg3 Determining registration distanceIt is difficult to determine the exact registration distance in experiment. If thereconstruction distance deviates from its correct value too far, reconstructionimage will become faint and poor quality, as out of fo

24、cus in common imagingsystem. So we should adopt a way to determine precise reconstructiondistance,d, namely d.The evaluation criteria is the image.s clearness. In normal imaging systems,people apply focusing functions as the evaluation criteria. Considering thesimilarity between the holographic reco

25、nstruction and the imaging course, thepaper also applies a focusing function as the evaluation criteria to determine theexact registering distance.The focusing functions normally applied can be divided into four types: grayand gradient function, frequency-domain function, informatics function andsta

26、tistics function. Gray evaluation function is easy to calculate and also robust.It can satisfy the demand of common focusing precision. We apply the intensitysum of reconstruction image as the evaluation function:min),(11MkNllkSThe calculation is described in Fig.2. The position occurring the turnin

27、gpoint correspondes to the best registration distanced, also equals to thereconstructing distanced.It should be indicated that if we only need to reconstruct the phase map ofthe object wave, the registration distance substituted into the calculationequation is permitted having a departure from its t

28、rue value.4 Spatial resolution of digital holography4.1Affecting factors of the spatial resolution of digital holographyIt should be considered in three respects: (1) sizes of the object and theregistering material, and the direction of the reference beam, (2) resolution ofthe registering material,

29、and (3) diffraction limitation.For pointx2on the object shown in Fig.3, the limits of spatial frequency are0211maxmaxtansinsinsinsinzxfRRFig.2 Determining reconstructing distance0211minmintansinsinsinsinzxfRRFrequency range is02110211tansintansinzxzxfso the range is unrelated to the reference beam.C

30、onsidering the resolution of registering material in order to satisfy thesampling theory, phase difference between adjacent points on the recording plateshould be less than , namely resolution of the registration material.cfff21)(minmax4.2 Expanding the spatial resolution of reconstruction imageExpa

31、nding the spatial resolution can be realized at least in three ways: (1)Reducing the registration distance z0can improve the reconstruction resolution,but it goes with reduction of the reconstruction area at the same ratio.Therefore,this method has its limitation. (2) Increasing the resolution and t

32、he imaging sizeofCCDwithexpensiveprice.(3)Applyingimage-synthesizingFig.3 Relationship between object and CCDtechnique11CCD captures a few of images between which there is smalldisplacement (usually a fraction of the pixel size) vertical to the CCD plane,shown in Fig.4(Schematic of vertical moving i

33、s the same).This method has two disadvantages. First, it is unsuitable for dynamic testingand can only be applied in the static image reconstruction. Second, because thepixel size is small (usually 5m to 10m) and the displacement should a fractionof this size (for example 2m), it needs a moving tabl

34、e with high resolution andprecision.Also it needs high stability in whole testing.In general, improvement of the spatial resolution of digital reconstruction isstill a big problem for the application of digital holography.5 Testing resultsFig.5 is the photo of the testing system. The paper does test

35、ing on two coins.The pixel size of the CCD is 4.65m and there are 1 3921 040 pixels. The firstis one Yuan coin of RMB (525 mm) used for image reconstruction byphase-shifting digital holography. The second is one Jiao coin of RMB (520mm) for the testing of deformation measurement also by phase-shifti

36、ng digitalholography.Fig.4 Image capturing by moving CCD along horizontal direction5.1 Result of image reconstructionThe dimension of the one Yuan coin is 25 mm. The registration distancemeasured by ruler is about 385mm. We capture our phase-shifting hologramsand reconstruct the image by phase-shift

37、ing digital holography. Fig.6 is thereconstructed image. Fig.7 is the curve of the auto-focus function, from whichwe determine the real registration distance 370 mm. We can also change thecontrolling precision, for example 5mm, 0.1 mm,etc., to get more course orprecision reconstruction position.5.2

38、Deformation measurementIn digital holography, the method of measuring deformation measurementdiffers from the traditional holography. It gets object wave before and afterdeformation and then subtract their phases to obtain the deformation. The studytested effect of heating deformation on the coin of one Jiao. The results areshown in Fig.8, Where (a) is the interferential signal of the object waves beforeand after deformatio