Photonics of nanoscale structural transitions in confined gallium
Photonics of nanoscale structural transitions in confined gallium
A pump-probe reflectometer, based on He-Ne and Argon-Ion lasers, has been developed and constructed to study, for the first time, the transient nonlinear reflectivity response of gallium/silica interfaces with sub-microsecond time resolution in the visible spectral region (514 - 633 nm). The response was measured at various interface temperatures for pump pulse durations in the range 150 ns - 10 ms and peak intensities of up to 8 kW/cm2 . At temperatures several degrees below gallium's melting point, 1 ms pump pulses were seen to induce reflectivity changes of up to 4%. Two characteristic types of the response have been observed, indicating the presence of both thermal and non-thermal mechanisms of the effect.
A reversible photoconductivity effect in an elemental metal has been discovered. The effect was studied in a-gallium confined at an interface with glass using 514 nm laser radiation. It has been found that the effect increases with temperature and reaches its maximum several degrees below the gallium's melting point, where conductivity of the metal's interface layer changes by as much as several percent. A new mechanism of photoconductivity has been proposed. It involves light-induced structural transformation in the layer ~ 15 nm thick, wherein a-gallium is converted into a new, metastable phase with different conductive properties.
It has been established that the large optical nonlinearity of gallium/silica interfaces reported in this work and elsewhere is achieved via light-induced metallization, i.e. conversion of a-gallium to a new, more metallic, more reflective phase of gallium. Rigorous temperature calculations have ruled out laser-induced thermal melting as a mechanism of the metallization for both quasi-cw and long-pulse (³ 10 ns) excitation.
University of Southampton
Fedotov, Vassili Alexandrovich
2002
Fedotov, Vassili Alexandrovich
Fedotov, Vassili Alexandrovich
(2002)
Photonics of nanoscale structural transitions in confined gallium.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
A pump-probe reflectometer, based on He-Ne and Argon-Ion lasers, has been developed and constructed to study, for the first time, the transient nonlinear reflectivity response of gallium/silica interfaces with sub-microsecond time resolution in the visible spectral region (514 - 633 nm). The response was measured at various interface temperatures for pump pulse durations in the range 150 ns - 10 ms and peak intensities of up to 8 kW/cm2 . At temperatures several degrees below gallium's melting point, 1 ms pump pulses were seen to induce reflectivity changes of up to 4%. Two characteristic types of the response have been observed, indicating the presence of both thermal and non-thermal mechanisms of the effect.
A reversible photoconductivity effect in an elemental metal has been discovered. The effect was studied in a-gallium confined at an interface with glass using 514 nm laser radiation. It has been found that the effect increases with temperature and reaches its maximum several degrees below the gallium's melting point, where conductivity of the metal's interface layer changes by as much as several percent. A new mechanism of photoconductivity has been proposed. It involves light-induced structural transformation in the layer ~ 15 nm thick, wherein a-gallium is converted into a new, metastable phase with different conductive properties.
It has been established that the large optical nonlinearity of gallium/silica interfaces reported in this work and elsewhere is achieved via light-induced metallization, i.e. conversion of a-gallium to a new, more metallic, more reflective phase of gallium. Rigorous temperature calculations have ruled out laser-induced thermal melting as a mechanism of the metallization for both quasi-cw and long-pulse (³ 10 ns) excitation.
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Published date: 2002
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Local EPrints ID: 464855
URI: http://eprints.soton.ac.uk/id/eprint/464855
PURE UUID: a85c44b2-9078-4e38-8969-216cf2e724ce
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Date deposited: 05 Jul 2022 00:05
Last modified: 05 Jul 2022 00:05
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Author:
Vassili Alexandrovich Fedotov
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