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Reference: Fletcher, Julian Hooton., (1993). Soft X-ray contact microscopy using laser generated plasma sources. DPhil. University of Oxford.Citable link to this page:


Soft X-ray contact microscopy using laser generated plasma sources

Abstract: The ultimate objective of this project was to develop a small, transportableX-ray microscope which would be able to view a wide range of biological specimenswithout the need for any type of sample preparation at a resolution greater than thatobtainable by conventional light microscopy (ie. about 250nm). Of the various possibleimplementations of X-ray microscopy currently being investigated, contact microscopywas chosen as being the most suitable for the development of such a small-scaleinstrument, while at the same time minimizing the effects on image quality ofradiation damage to the biological specimen.The requirement for a high brightness pulsed X-ray source of less than 50nsduration for illumination of the specimen was met by the production of laser generatedplasmas. These were formed by focusing a 2.2J KrF laser beam, of wavelength 248nmand duration 20ns, onto the surface of one of a number of different target materials. Inorder to obtain the large intensities required for the production of a sufficiently hightemperature plasma, a doubly pre-ionized, discharge-pumped amplifier KrF laser wasdeveloped. This was seeded by a smaller oscillator laser by means of a coupled unstableresonator configuration. A number of different cavity arrangements were investigatedand an output beam divergence of 2.5 times the diffraction limit was achieved.The plasmas generated by focusing the laser beam to an intensity of 1014W/cm2onto carbon, titanium, molybdenum and tungsten targets were characterized as fully aswas necessary for their use in the X-ray microscope. Preliminary investigations on theuse of a grazing incidence ellipsoidal mirror to focus the emitted X-rays onto thespecimen of the microscope were made and such an optical component wasmanufactured and tested.Finally, numerous images of a number of different biological specimens weremade and resolutions of better than 100nm were achieved. Images were read out usinga Park Scientific Instruments atomic force microscope, which enabled the entiremicroscopy process to be carried out in a single working day. The system is now inroutine use and can produce more than ten images per session.

Type of Award:DPhil Level of Award:Doctoral Awarding Institution: University of Oxford Notes:The digital copy of this thesis has been made available thanks to the generosity of Dr Leonard Polonsky

Bibliographic Details

Issue Date: 1993Identifiers

Urn: uuid:444fa0f3-d9b7-40ff-a8e0-1e4fd5ce03c5

Source identifier: 602830133 Item Description

Type: Thesis;

Language: eng Subjects: X-ray microscopy Lasers in biology Image processing Plasma generators Tiny URL: td:602830133


Autor: Fletcher, Julian Hooton. - institutionUniversity of Oxford facultyMathematical and Physical Sciences Division - - - - Bibliograph



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