Browsing by Author "Bellerby, J."

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    Interaction of laser radiation with urinary calculi
    (2009-11-25T17:07:23Z) Mayo, M. E.; Ahmad, S. R.; Bellerby, J.
    Urolithias, calculus formation in the urinary system, affects 5 – 10% of the population and is a painful and recurrent medical condition. A common approach in the treatment of calculi is the use of laser radiation, a procedure known as laser lithotripsy, however, the technique has not yet been fully optimised. This research examines the experimental parameters relevant to the interactions of the variable microsecond pulsed holmium laser (λ = 2.12 μm, τp = 120 – 800 μs, I ~ 3 MW cm-2) and the Q-switched neodymium laser (λ = 1064 nm, τp = 6 ns, I ~ 90 GW cm-2) with calculi. The laser-calculus interaction was investigated from two perspectives: actions that lead to calculus fragmentation through the formation of shockwave and plasma, and the prospect of material analysis of calculi by laser induced breakdown spectroscopy (LIBS) to reveal elemental composition. This work is expected to contribute to improved scientific understanding and development of laser lithotripsy. The results support the general model of thermal and plasma processes leading to vaporization and pressure pulses. Nd:YAG laser interaction processes were found to be plasma-mediated and shockwave pressure (~ 12 MPa) dependent on plasma and strongly influenced by metal ions. Ho:YAG laser-induced shockwaves (~ 50 MPa) were found to be due to direct vaporisation of water and dependent on laser pulse duration. The characteristics of the pressure pulse waveforms were found to be different, and the efficiency and repeatability of shockwave and the nature of the dependencies for the lasers suggest different bubble dynamics. For the Nd:YAG laser, LIBS has been demonstrated as a potential tool for in situ analysis of calculus composition and has been used for the identification of major and trace quantities of calcium, magnesium, sodium, potassium, strontium, chromium, iron, copper, lead and other elements.
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    Surface enhanced raman spectroscopy for ultra-sensitive detection of energetic materials
    (2010-11-03) Syed, A. A.; Ahmad, S. R.; Bellerby, J.
    The prospect of ultra-sensitive detection of molecular species, particularly those of energetic materials, has prompted the present research initiative. The combination of metal surface nano-technology and Raman spectroscopy has given rise to ‘Surface Enhanced Raman Spectroscopy’ (SERS). This is a very sensitive technique and has proved to be capable of detecting a single molecule. SERS was demonstrated by recording Raman spectra of the sample molecules adsorbed on various specially prepared SER-active surfaces both in the form of a colloidal suspension and on the solid roughened surfaces. Using a gold colloidal suspension, pyridine has been detected down to 10-11 molar (M) concentration. A silver slab was roughened to a dimension of a nano-scale by etching in nitric acid solution to make SER-active surface. Pentaerythritol Tetranitrate (PETN) explosive was detected using this surface after its 10-2 M solution was dropped, dried and washed (of any residue) from the surface. Lithographically engineered silver structures in the form of nanoarrays having a number of silver structures of approximately 106 in a region of 0.1 mm2 have been used for SERS. The major noise contribution to the scattering from impurities in an ordinary glass substrate has been eliminated by replacing glasses as substrates with pure quartz discs. The headspace vapours from peroxide explosives, Triacetone Triperoxide (TATP) and Hexamethylene Triperoxide Diamine (HMTD), were detected at approximately 70 parts per million (ppm) and 0.3 ppm concentrations respectively using a portable commercial Raman Spectrometer. PETN was also detected from its headspace vapour at about 18 parts per trillion (ppt) in spite of it having a much lower vapour pressure. The possibility of desorption of adsorbed molecules from a nano-structured surface by laser irradiation has been demonstrated experimentally with the aim of reusability of SER-active surfaces. Also demonstrated was the enhancement in Raman intensity through resonance Raman effect spectroscopy for the future use in surface enhanced resonance Raman spectroscopy (SERRS).