Time and temperature dependence of stimulated brillouin scattering in fused silica
Stanton, Richard Heath
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https://hdl.handle.net/2142/25805
Description
Title
Time and temperature dependence of stimulated brillouin scattering in fused silica
Author(s)
Stanton, Richard Heath
Issue Date
1969
Doctoral Committee Chair(s)
Gilman, J.J.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
time dependence
temperature dependence
stimulated brillouin scattering
fused silica
acoustic phonon lifetime
Language
en
Abstract
Several aspects of stimulated Brillouin scattering which
relate to the determination of acoustic phonon lifetime (Tp) have
been investigated. Fused silica was selected as the principal
material to be studied because of its optical and acoustic isotropy
and its availability in large, optical quality samples.
Also, it has the advantage of a distinct dependence of acoustic
attenuation on temperature. The main difficulty in using stimulated scattering to determine
phonon lifetimes is an uncertainty of whether or not steady-state scattering is achieved during the finite length of the laser pulse. Theoretically, this problem is most acute in solids, where acoustic phonon lifetimes can be of the same order
of magnitude as the laser pulse length. This situation was investigated experimentally and it was found that (a) the rise of Brillouin light is much faster than predicted theoretically, and
(b) a reasonable fit to steady-state predictions can be obtained when one considers the peak Brillouin power as a function of the laser intensity. Apparently the scattering process adjusts to steady-state conditions in less than 8 nanoseconds rather than in the longer intervals predicted by theory. This conclusion is applied to observed variations in the scattering with temperature, and the corresponding values of Tp are calculated.
Similar, though less extensive, studies were conducted using Plexiglas for the scattering medium and essentially the same conclusions were reached. This fact suggests that we are dealing with general properties of stimulated Brillouin scattering and not just anomalous behavior in the specific case of fused silica.
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