Brillouin Scattering

The colossal piezoelectric effect of relaxor-based ferroelectrics has attracted much attention due to the technological importance of the conversion between electric and mechanical energies. The mechanism of the significant field effect on piezoelectric properties in this disordered system has become one of the current topics in pure and applied physics. The important key factor in the understanding of relaxors is polar nanoregions (PNRs) which appear at temperatures far above the dielectric maximum or Curie temperature. PNRs play a dominant role in the formation of unique characteristics of relaxors and are regarded to be caused by spatial and dynamic heterogeneity. However, a detailed microscopic picture of their evolution depending on temperature or electric field is still the subject of controversy. The elastic and dynamical properties of the Pb(B1/3B′2/3)O3-type relaxor-based ferroelectrics and their solid solutions with pure ferroelectrics have recently been studied extensively by the broadband micro-Brillouin scattering spectroscopy (BMBS) to clarify the role of PNRs. This paper reviews the recent progress in the understanding of fast dynamics of PNRs of typical relaxor-based ferroelectrics of (1−x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 and (1−x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 in the gigahertz frequency range achieved by using BMBS.

Optical fiber sensors have become a widely used tool to perform life-long
monitoring of large structures. Different set-ups of sensors can be used to obtain
information at different scopes. In this paper, the application of a portable Brillouin
optical time domain analysis sensor applied to reinforced concrete beams is
presented. The sensor is made up of a single-mode optical fiber applied to the
structure that enables the measurement of tensile and compressive axial strain along
the beams. The fiber is embedded into a concrete casting without particular
installation care and fixed along the reinforcement bars so that a complete correlation
can be obtained regarding axial strain and displacements at different heights of the
beam in linear and non-linear bending response. The use of four sensing fibers
positioned along the beam's length at different vertical positions makes it possible to
read the strain variation within the cross-section. In accordance with Bernoulli’s
hypothesis, this allows curvature diagrams to be obtained across the structure. The
measured curvature is used to set up the moment–curvature relationship, which
highlights the possibility of the sensor monitoring structures continuously in space
and time. From the experiment the theoretical and experimental results are compared
and it will be seen how they can actually be reliable in order to perform a monitoring
on civil engineering structures. This allows to validate the response of a distributed
fiber optic sensor and to promote its use for structural health monitoring (SHM).

The temperature resolution of a fibre-optic distributed temperature sensor based on taking the ratio of the temperature sensitive backscattered spontaneous Brillouin signal to the corresponding Rayleigh signal depends on the optical signal-to-noise of the receiver system and the amplitude fluctuations in the Rayleigh signal. The amplitude fluctuations or coherent Rayleigh noise have been investigated experimentally as a function of detection bandwidth, source bandwidth and spatial resolution and showed good agreement with theory.

The directional dependence (angular dispersion) of surface acoustic phonons propagating on {loo}, {l lo}, and {ill) oriented planes of nickel single crystals has been measured by Brillouin scattering and continuous wave scanning acoustic microscope. All the elastic constants Cll, C12, C,, are obtained from the angular dispersion of each plane separately. These are compared with the elastic constants determined with conventional ultrasonic measurements on the same specimens. The difference in the sampling depth or the approximate depth of propagation of the acoustic waves into the specimen in each technique is used to characterize the extent of the polish-induced damage zone in the sample.

We report on the use of a cost-effective erbium-doped based optical preamplifier in a single-ended distributed fiber-optic sensor to improve receiver sensitivity and hence measurement range. The improved accuracy of spontaneous Brillouin measurements was demonstrated in a 23km sensor and was limited by amplified spontaneous emission from the preamplifier, which was verified theoretically. Reduction of amplified spontaneous emission was achieved with a 0.37nm in-fiber Bragg grating. A signal-to-noise improvement of 17dB was achieved and supported by theory, which translates to approximately 40km range improvement for a single-mode sensing fiber having losses of 0.2dB/km at 1550nm.