Postgraduate Thesis uoadl:1317966 119 Read counter

Κατεύθυνση Φυσική των Υλικών (ΒΑΣΙΚΗ ΦΥΣΙΚΗ)

Library of the School of Science

Library of the School of Science

2016-01-04

2016

Ζδάγκας Απόστολος

Νικόλαος Στεφάνου Καθηγητής (Επιβλέπων), Μαρία Καλαμιώτου Αναπλ. Καθηγήτρια, Εμμανουήλ Συσκάκης Επίκ. Καθηγητής

Θεωρητική Μελέτη της Σκέδασης Brillouin από Σφαιρικά Σωματίδια

Greek

Theoretical Study of Brillouin Light Scattering by Spherical Particles

Brillouin light scattering is the inelastic light scattering due to the spatial

and temporal

variations of the refractive index of a material. These variations are due to

collective oscil-

lations of a quantity in the material which, in our case, are the collective

lattice oscillations

(phonons). These oscillations are in the GHz frequency range and this is why

the deve-

lopment of lasers and the invention of the multi-pass tandem Fabry-Perot

interferometer

was needed in order to use the effect as a spectroscopic technique. This

technique has

already been used for the characterization of the elastic properties of solids

and liquids

but with the advent of meso-scale periodic structures, in which the dominant

frequencies

are in the GHz range, it soon became apparent that the technique could be used

for the

characterization of phononic microstructures. In the last decade, a lot of e

ffort has been

devoted in order to explain the Brillouin spectrum of such periodic

microstructures of

spherical particles. The effort was focused on indirect explanations either by

calculating

the eigenmodes, the scattering cross section and the density of states of the

individual

particles or the frequency band structure of the phononic crystal, as well as

using group

theory. It became clear that only a detailed theoretical study, which takes

into account

the interaction of light with the elastic field, can give the correct relative

intensities of the

scattered light. Such a theoretical approach of the Brillouin light scattering

by a spherical

particle, based on Green's functions, is attempted in the present thesis. Using

the work of

T. Still et al., J. Phys. Chem. Lett. 1, 2440-2444 (2010) as a starting point,

we improve

the computation time and the accuracy of the calculations and establish the

theoretical

foundations for a thorough description of the effect as well as the extension

of Brillouin

light scattering calculations to periodic structures.

and temporal

variations of the refractive index of a material. These variations are due to

collective oscil-

lations of a quantity in the material which, in our case, are the collective

lattice oscillations

(phonons). These oscillations are in the GHz frequency range and this is why

the deve-

lopment of lasers and the invention of the multi-pass tandem Fabry-Perot

interferometer

was needed in order to use the effect as a spectroscopic technique. This

technique has

already been used for the characterization of the elastic properties of solids

and liquids

but with the advent of meso-scale periodic structures, in which the dominant

frequencies

are in the GHz range, it soon became apparent that the technique could be used

for the

characterization of phononic microstructures. In the last decade, a lot of e

ffort has been

devoted in order to explain the Brillouin spectrum of such periodic

microstructures of

spherical particles. The effort was focused on indirect explanations either by

calculating

the eigenmodes, the scattering cross section and the density of states of the

individual

particles or the frequency band structure of the phononic crystal, as well as

using group

theory. It became clear that only a detailed theoretical study, which takes

into account

the interaction of light with the elastic field, can give the correct relative

intensities of the

scattered light. Such a theoretical approach of the Brillouin light scattering

by a spherical

particle, based on Green's functions, is attempted in the present thesis. Using

the work of

T. Still et al., J. Phys. Chem. Lett. 1, 2440-2444 (2010) as a starting point,

we improve

the computation time and the accuracy of the calculations and establish the

theoretical

foundations for a thorough description of the effect as well as the extension

of Brillouin

light scattering calculations to periodic structures.

Brillouin scattering, Inellastic light scattering, Eigen-modes of a spherical particle, Photo-elastic effect

No

0

Yes

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