阴极射线管单晶膜屏幕外文文献英文

Radiation Measurements 42 2007 933 936 Singlecrystallinefi lmscreensforcathode raytubes Newlifeoftelevision scanningopticalmicroscopy Z D Hrytskiva Y Zorenkob V Gorbenkob A D Pedana W I Shkliarskyia aDepartment of Radio Devices and Systems Lviv Polytechnic National University S Bandery 12 Lviv 79013 Ukraine bDepartment of Electronics Ivan Franko National University of Lviv 107 Gen Tarnavskyj Str 79017 Lviv Ukraine Received 20 December 2006 accepted 1 February 2007 Abstract Advantages of television scanning optical microscopy are discussed in comparison with cameral microscopy Peculiarities of new types of cathode ray tubes with single crystalline fi lm screens as a source of scanning beam are described 2007 Published by Elsevier Ltd Keywords Single crystalline fi lm Cathode ray tubes Scanning optical microscopy 1 Introduction It is commonly known that there are two important steps that signifi cantly improve the microscopy possibilities in particu lar the optical microscopy 1 usage of television methods and means and then 2 use of a computer for microscope control and image processing The fi rst step not only allows receiv ing electrical signal of microobject image and enhancing the convenience of image observation on large screen but also to digitize image that is necessary for computer application The second one is used to store images in electronic format and to large extent to enhance the quality and information of the images Television microscopy is especially effi cient for exam ination of dynamic fi rst of all moving objects At the same time objects can also be examined as in the case of microscope with digital photo camera usage Thus television microscope can be defi ned as an optical device supplemented with units that realize the principle of element by element dynamic image presentation Another term used in similar meaning is video microscopy however in practice this term usually concerns to the optical microscopes supplemented with classical television camera we use in this case the term cameral microscopy Corresponding author E mail address zorenko electronics wups lviv ua Y Zorenko Deceased 1350 4487 see front matter 2007 Published by Elsevier Ltd doi 10 1016 j radmeas 2007 02 043 One different television method is employed in scanning op tical microscopy small light spot created by light beam probe scans micro object s fi eld of view transmitted or refl ected light goes on to a photo receiver and the last forms a video sig nal The beam should not necessarily be the visible light it can be the ultraviolet or infrared Profound intelligence con cerning scanning optical microscopy can be found in Wilson and Sheppard 1984 This book is especially interesting for us because it shows that the beginning of scanning optical mi croscopy SOM was connected with cathode ray tube CRT as a source of light scanning beam 1951 The content of our paper is also based on scanning CRT usage 2 Advantages of scanning microscopy A lot of papers pieces of information and some books are connected with video microscopy For one example see Shinge and Venneth 1997 There is little new information concern ing SOM although it has been recently paid attention to main advantages of SOM Color 2005 Television scanning opti cal microscopy has signifi cant advantages in comparison with television cameral microscopy 1 Higher spatial resolution 2 Absence of diffraction contour outlining the image 3 Point type illumination and therefore less limitations from the object destruction point of view 934Z D Hrytskiv et al Radiation Measurements 42 2007 933 936 4 Possibility of fl exible choice of an illumination mode by optical beam in particular with the aim of increasing or decreasing contrast without computer processing 5 Possibility of smooth electronic alteration of magni fi cation 6 Possibility to use optical beam for selective action on the object It has to be pointed out that contemporary television camera microscopes are based on CCD cameras The last have discrete structure of sensitive part as an array of sensitive elements pixels with defi nite dimension As it is known the resolved spatial period with this array in the best case may be estimated as 2a where a is the dimension of array sensitive element As a result the spatial resolution is somewhat lower than in scanning variant with scanning spot diameter a since in this case the resolution is possible if the neighbouring spots partly overlay one another Under intensive illumination there occurs a charge channel off phenomenon on the sensitive surface of CDD It is equiv alent to increasing the pixel dimension and so to decreasing the spatial resolution Something similar would be in scanning optical microscope as a result of increasing the spot diameter on the CRT screen however such an effect in CRT is absent As it is known CCDs have limitations concerning the lowest frequency of charge shift in the cells If this frequency be too low the charges also would channel off with the same phe nomena of spatial resolution decrease There is no such lim itation in scanning microscopy The scanning speed may be low and that may be used for the level of signal enhancement as well as if it is needed for CRT phosphor decay elimina tion Colour cameral television microscope may de designed on the base of single colour CCD or three monochrome CCDs In the fi rst case the spatial resolution becomes smaller since every pixel of array must have sub pixels in main colours R G B If monochrome CCDs are used the optical system be comes very complicated the radiation is absorbed in the sys tem and sensitivity decreases It is also diffi cult to ensure the same optical magnifi cation in all three channels It is enough to have CRT with white colour of radiation and appropriate colour fi lters in front of photo sensors in the case of scanning microscopy Concerning advantages of scanning microscopy in image magnifi cation alteration it should be pointed out that in cameral microscopes the scale alteration is realized by appropriate soft ware of image processing usage As a result under increasing magnifi cation the pixel structure of image becomes visible In scanning microscope the image remains continuous since the magnifi cation is realized by scanning raster dimension alter ation Of special interest is the possibility of obtaining in scanning optical microscopy some larger spatial lateral resolution that is equivalent to larger useful magnifi cation It is well known that theoretical limit in spatial resolution is determined by the diffraction phenomena Limited spatial resolution of usual and so cameral microscope is estimated in accordance with the Raleigh criterion and for its quantitative estimation the follow ing formula is used R 0 61 A where R is the smallest distance under which the point objects are recorded as different ones is the radiation wavelengths and A is the objective numerical aperture The coeffi cient of illumination modulation in the image plane is equal to 22 5 This is a result of illuminations summation in the images of neighbour point objects each of which is described by the Erie law Action of summation in SOM is absent One more advan tage thatisespeciallyusefulforbiology consistsinthefactthat SOM allows unlike the electron microscopy to perform exami nation of live micro objects because the special preparation of objects is not needed Of course magnifi cation of SOM is ade quate only to the lowest magnifi cation of electron microscope Scanning microscopes on the base of CRTs have some dis advantages too Among them CRT sensitivity to external magnetic fi elds necessity to use high stability sources for scanning CRT con trol and supply sometimes relatively low intensity of scanning beam intensity of scanning spot in the object plane decrease if the beam is defl ected from the screen centre necessity of spot dimension correction if the beam is de fl ected from the screen centre limitation concerning the speed of scanning determined by screen phosphor time decay presence of relatively considerable noise of scanning CRT screen with powder phosphor 3 Special cathode ray tubes Some of the disadvantages mentioned above can be over come if special CRT with very high spatial resolution VHSR is used An attempt to fi nd information about CRT with high spatial resolution usually is completed with information con cerning the spatial resolution in lines per screen and is equal to 1000 2000 Such CRTs are designed for displays have large screen dimensions and cannot be used for microscope as scan ning CRTs There is a reason to discuss this parameter of CRT as a specifi c spatial resolution in lines per mm Thus special CRT with VHSR should have specifi c spatial resolution at a level of 50 100 lines per mm There is no necessity to have a large screen because if we would like to render image as usu ally in a monitor screen with e g 2000 pixels in line it means that the line in the screen of scanning CRT has a dimension of 2000 pixels 1000 lines per mm 2mm It was the period 1960 1980 when CRTs with VHSR were produced for different purposes such as microfi lm fi lm scan ning for precision image acquisition high quality image form ing as a result of remote sensing etc High level of screen noise and insuffi cient intensity of light are most disadvantages of such CRTs Essential improvement of scanning optical microscope on the base of CRT may be received if CRT of new type is Z D Hrytskiv et al Radiation Measurements 42 2007 933 936935 used CRT with single crystal screen Denisiuk et al 1988 or single crystalline fi lms SCF screen Zorenko et al 1998 The later screen is manufactured based on the SCF of the Y3Al5O12Ce or Lu3Al5O12Ce garnets with a diameter of 30 65mm and a SCF thickness of 3 5 m grown by Liquid Phase Epitaxy onto undoped Y3Al5O12substrates with a thick ness of 0 9 2mm from melt solution based on PbO B2O3 fl ux and R2O3 R Y Lu and Al2O3high purity 4N 5N oxides The optimal range of CeO2oxide in MS was deter mined experimentally in a range of 7 12mole for obtaining the maximum of the SCF screens cathode luminescence light yield in the 300 350 Wt sR range Inanothervariantthescreenismanufacturedasaplateofsin gle crystal yttrium aluminium garnet with admixture activators that are introduced at the process of crystal growth Such a screen has good thermo conductive properties that allows to use electron beam of higher intensity than under powder phosphor usage and thus to receive enhanced luminosity of screen lumi nescence The screen does not destruct under very low speed of scanning and even unmoving spot Especially useful is the suffi ciently lower pseudo random screen noise It averages to 1 2 whereas the powder screens because of grain struc ture have noise of 10 15 Unfortunately the works were aimed on CRTs Itoh and Ozawa 2006 with single crystal screen improvement that were discontinued At the same time renewal of these works would allow to expand the scopes of microscope usage 4 Two advantages of scanning optical microscopy In this section we would like to emphasize two important advantages of scanning optical microscopy The fi rst one is higher spatial lateral resolution in compar ison with usual and also the cameral television microscopy as it was mentioned above Our aim was to confi rm this experi mentally We have used a sample of television scanning opti cal microscope designed and produced by us As a test object fi bre optic faceplate served with maximum dimension of the fi bre measured on optical microscope about 3 m The image of fi bre optic faceplate received from the screen of microscope monitor is shown in Fig 1a The measurement performed directly in the image allows us to estimate the size of the gap between fi bres equal to about 0 24 m Atthesametimethesharpnessoffi bres edgesisquite high anditisevidentthatthegapatminimumtwicesmallercan be resolved that is about 120nm Used in the microscope CRT with VHSR creates light beam in the yellow green zone of radi ation with a maximum at wavelength of 550nm In accordance with the above mentioned formula resolved distance in optical andthusincameralmicroscope R 0 61 550 0 65 516nm where 0 65 is the numerical aperture of microscope objective In other words the spatial resolution of the scanning optical microscope is about four times better than that of cameral mi croscope The second advantage of scanning microscopy is the ab sence of contour around the image parts By the way there are no outlining in the image in Fig 1a To show this advantage Fig 1 Image of fi bre optic faceplate a image of black white border in cameral microscope b and scanning microscope c 936Z D Hrytskiv et al Radiation Measurements 42 2007 933 936 in another way we have performed numerical analysis of the diffraction action on image creation The last was an edge between the black and white semi planes the method that is usually used to investigate transmission function Calculated transmission functions for the cameral and scanning micro scopes were then interpreted as illumination distribution The results of modelling are shown in Fig 1b cameral microscope and 1c scanning microscope In the case of cameral micro scope the contour outlining is very visible and there