Brillouin scattering

About: Brillouin scattering is a research topic. Over the lifetime, 11426 publications have been published within this topic receiving 178306 citations.

Brillouin Scattering Near the Glass Transition of Polymethyl Methacrylate

Abstract: Brillouin scattering of laser light has been used to measure the frequency of hypersonic sound waves in the range of 1010 Hz in PMMA as a function of temperature through the glass‐transition region. A discontinuity in the temperature coefficient of sound velocity is observed at the glass‐transition temperature; this is explained as a consequence of a corresponding discontinuity in the temperature coefficient of the specific volume (thermal expansion coefficient). The ratio of the light scattered by isothermal density fluctuations to that scattered by adiabatic density fluctuations was also measured. This ratio was large and did not change appreciably near the glass‐transition temperature. The value of the Landau‐Placzek ratio is approximately what one would expect from previously observed ultrasonic‐velocity‐dispersion data as a function of temperature well above the glass‐transition temperature. Both the velocity and intensity ratio data indicate that no velocity‐dispersion effects are present for the hypersonic sound waves up to temperatures 35° above the glass‐transition temperature. These results also indicate that the glass transition is not a classical second‐order phase transition.

Degenerate four-wave mixing in plasmas.

Abstract: We report an analysis of degenerate four-wave mixing in uniform plasmas and show that the magnitude of the third-order susceptibility (varying as lambda(2)) can be comparable to (10(-11) esu for lambda = 10.6 microm) or orders of magnitude larger (10(-3) esu for lambda= 10 cm) than the corresponding susceptibility in typical nonlinear materials. The nonlinear contribution to the macroscopic current resulting from the ponderomotive force is generated from the two-component fluid model by means of a linearized perturbation scheme. Numerical estimates of the nonlinear susceptibility show that relatively large signals can be produced easily without significant problems from competing physical phenomena such as self-focusing or stimulated Brillouin and Raman scattering.

BOTDA measurements tolerant to non-local effects by using a phase-modulated probe wave and RF demodulation.

Abstract: We demonstrate a Brillouin optical time domain analysis sensor based on a phase-modulated probe wave and RF demodulation that provides measurements tolerant to frequency-dependent variations of the pump pulse power induced by non-local effects. The tolerance to non-local effects is based on the special characteristics of the detection process, which provides an RF phase-shift signal that is largely independent of the Brillouin gain magnitude. Proof-of-concept experiments performed over a 20-km-long fiber demonstrate that the measured RF phase-shift spectrum remains unaltered for large frequency-dependent deformations of the pump pulse power. Therefore, it allows the use of a higher optical power of the probe wave, which leads to an enhancement of the detected signal to noise ratio. This can be used to extend the sensing distance, to improve the accuracy of the Brillouin frequency shift measurements, and to reduce the measurement time.

Stimulated brillouin scattering in the presence of external feedback

Abstract: We investigate theoretically and experimentally the process of stimulated Brillouin scattering (SBS) in the presence of weak feedback in a single-mode optical fiber. The threshold for the occurrence of Brillouin oscillation can be considerably lower than the threshold for normal SBS. The spectrum of the emitted Stokes light exhibits an extreme narrowing near and above the oscillation threshold. The Stokes intensity is found to exhibit various types of periodic and stable behavior.

Overcoming Nonlocal Effects and Brillouin Threshold Limitations in Brillouin Optical Time-Domain Sensors

Abstract: We demonstrate, for the first time to our knowledge, a Brillouin optical time-domain analysis (BOTDA) sensor that is able to operate with a probe power larger than the Brillouin threshold of the deployed sensing fiber and that is free from detrimental nonlocal effects. The technique is based on a dual-probe-sideband setup in which an optical frequency modulation of the probe waves along the fiber is introduced. This makes the optical frequency of the Brillouin interactions induced by each probe wave on the pump vary along the fiber so that two broadband Brillouin gain and loss spectra that perfectly compensate are created. As a consequence, the pulse spectral components remain undistorted, avoiding nonlocal effects. Therefore, very large probe power can be injected, which improves the signal-to-noise ratio (SNR) in detection for long-range BOTDA. Moreover, the probe power can even exceed the Brillouin threshold limit due to its frequency modulation, which reduces the effective amplification of spontaneous Brillouin scattering in the fiber. Experiments demonstrate the technique in a 50-km sensing link in which 8 dBm of probe power is injected.