Stimulated Brillouin scattering slow-light-based fiber-optic temperature sensor

We propose and experimentally demonstrate a method for temperature sensing using stimulated Brillouin scattering (SBS)-based slow light. The approach relies on temperature dependence of the Brillouin frequency shift in a fiber, hence the time delay of an input probe pulse. By measuring the delay, temperature sensing can be realized. We achieve temperature measurement in a 100 m single-mode fiber (SMF) using a cw pump. The main temperature-sensing range is ～18°C from the room temperature, limited by the SBS gain bandwidth. To apply the technique for measurement of a shorter fiber segment, a pulsed pump is used to introduce SBS slow light. Temperature sensing is achieved in a 2 m SMF with a main sensing range of around ～25°C. The scheme is easily implemented, exhibits a relatively high temperature sensitivity with a resolution better than 1.0°C, and is potentially applicable for distributed sensing.     

Observations of wavefront reproduction by stimulated Brillouin and Raman scattering as a function of pump power and waveguide dimensions

Experimental investigations have been made of wavefront reproduction (WFR) by backward stimulated Raman scattering (SRS) and backward stimulated Brillouin scattering (SBS) in CS₂ and C₇H₆O using a linearly polarized ruby pump at λ=0.694 μm. The studies were carried out as a function of the length and cross-section of the optical waveguide and the pump power at the input to the nonlinear medium; curves showing the percentage of nonreproduced backscattered radiation versus power into the waveguide are presented. In all of the cases studied the degree of reproduction by SBS was higher than that by SRS and the efficiency of WFR for both SBS and SRS improved as the pump power into the waveguide was increased, the bore diameter of the lightpipe decreased, and the length of active media decreased.     

Simultaneous temperature and strain measurement with combined spontaneous Raman and Brillouin scattering

We report on a novel method for simultaneous distributed measurement of temperature and strain based on spatially resolving both spontaneous Raman and Brillouin backscattered anti-Stokes signals. The magnitude of the intensity of the anti-Stokes Raman signal permits the determination of the temperature. The Brillouin frequency shift is dependent on both the temperature and the strain of the fiber; once the temperature has been determined from the Raman signal, the strain can then be computed from the frequency measurement of the Brillouin signal.     

Filamentation and stimulated Brillouin scattering in a turbulent plasma

This paper presents a theory of filamentation and stimulated Brillouin scattering (SBS) of high-frequency electromagnetic radiation in a weakly collisional plasma with ion-acoustic turbulence. When the square of the wavelength of the plasma perturbations is less than the product of the two mean free path lengths of an electron with respect to its collisions with turbulent fluctuations and with electrons, the influence of cold highly collisional electrons on the parametric instabilities becomes apparent. It is shown that the plasma turbulence lowers the filamentation threshold, and the SBS threshold can be either lowered or raised. The dependence of the SBS and filamentation thresholds on the electron mean free path length in the turbulent plasma and on the anisotropy of the plasma turbulence is determined. The corresponding dependence of the spatial scale of the most efficiently growing filaments and their spatial growth rate are found. Zh. éksp. Teor. Fiz. 113, 629–645 (February 1998)     

Brillouin scattering in layered structures

Theoretical and experimental results on Brillouin scattering in inhomogeneous materials are presented: Normal elastic modes and Brillouin intensities have been calculated for a periodic layer system. Measurements on semicrystalline polybutene-1 are discussed in terms of the theoretical results. Both theory and experiment yield several Brillouin lines in VV scattering instead of the one peak characteristic for homogeneous specimens.     

Accuracy enhancement in Brillouin scattering distributed temperature sensor based on Hilbert transform

The scattering optical signal of OTDR based Brillouin scattering distributed sensor is very weak and have a frequency width of several decades megahertz, so it is hard to perform the traditional analogue coherent demodulation. A novel optical coherent detection based on Hilbert transform is presented here. In detail, Brillouin backscattering light is coherent detected with the reference light, which is modulated by microwave electric optical modulator to produce frequency-adjustable light, then the detected photocurrent signal is demodulated by digital signal processing based on Hilbert transform, and at last the distributed sensing signal with better S/N ratio is gained, which can enhance the performance of the sensor. The simulation and experimental results of the detection method are given.     

Brillouin scattering and the CMB

Brillouin scattering of photons off the density fluctuations in a fluid is potentially important for cosmology. We derive the Brillouin spectral distortion of blackbody radiation, and discuss the possible implications for the cosmic microwave background. The thermal Sunyaev-Zeldovich effect is slightly modified by Brillouin distortion, but only at very long wavelengths.     

Potential of Brillouin scattering in polymer optical fiber for strain-insensitive high-accuracy temperature sensing

We investigated the dependences of Brillouin frequency shift (BFS) on strain and temperature in a perfluorinated graded-index polymer optical fiber (PFGI-POF) at 1.55 μm wavelength. They showed negative dependences with coefficients of -121.8 MHz/% and -4.09 MHz/K, respectively, which are -0.2 and -3.5 times as large as those in silica fibers. These unique BFS dependences indicate that the Brillouin scattering in PFGI-POFs has a big potential for strain-insensitive high-accuracy temperature sensing.     

Effect of water temperature on pulse duration and energy of stimulated Brillouin scattering

The water temperature has a strong effect on the kinematic viscosity, which is inversely proportional to the phonon lifetime and the gain coefficient. The higher the temperature is, the smaller the kinematic viscosity is, and the larger the phonon lifetime is. At a low pump power and a short focal length, we can derive a single-peak stimulated Brillouin scattering (SBS) pulse. The duration of this single-peak SBS pulse depends mainly on the phonon lifetime of water. With the increase of the water temperature, the duration of such a single-peak SBS pulse will become longer, and the SBS energy will become higher for the gain coefficient, which is related to the phonon lifetime. Therefore, varying the medium temperature can lead to the changes of SBS pulse duration and SBS energy.     

Resonant Brillouin scattering near the a exciton in CdS

We have studied resonant Brillouin scattering in CdS by tuning a narrow-band cw dye laser through the A-exciton transition at helium temperatures. We observed besides the resonance enhancement a pronounced asymmetry of the Stokes and anti-Stokes shift and a dramatic increase of the Brillouin shifts as a function of laser frequency. These observations are consistent with a model of exciton-polariton scattering by longitudinal acoustic phonons. For incident frequencies higher than the longitudinal exciton frequency additional features are found which cannot be explained by the two-branch model for exciton-polaritons.     

Stimulated Brillouin scattering in a plasma with ion-acoustic turbulence

A theory of stimulated Brillouin scattering (STBS) in a plasma with ion-acoustic turbulence is developed using concepts of parametric instability under conditions when equations of two-temperature hydrodynamics can be used to describe ion-acoustic perturbations of the electron density. The temporal growth rate of the absolute instability and the spatial gain of the scattered wave are determined. The dependence of the threshold density of the radiation flux on the angle between the scattering wave vector and the direction of anisotropy of the turbulent noise is described. A new effect of STBS forbiddenness caused by anomalous turbulent heating of the ions is predicted for a plasma with a high level of turbulent noise.     

布里渊散射及其在激光雷达中的应用

在简要介绍布里渊散射的基本性质的基础上,重点介绍了布里渊散射在激光雷达中的应用。主要分析了布里渊散射在水中声速测量、粘滞系数的测量和水中目标探测方面的原理和技术实现。     

Brillouin scattering in cubic potassium cyanide

The temperature dependence of the elastic shear constant C₄₄ of cubic potassium cyanide has been measured by optical Brillouin spectroscopy in the temperature range from 300-168 K. A strong softening of the constant C₄₄ was found in agreement with the results of ultrasonic and neutron measurements.     

Brillouin scattering in microstructures involving GaAs

Light interaction with Rayleigh Surface Waves propagating parallel to the surface of GaAs substrates implanted with heavy ions has been used for the determination of the acoustic velocity in amorphous GaAs. A complete analysis of the peak-width of the scattered light from folded acoustic modes, including the contribution of the phonon lifetime and the light absorption, is presented for superlattices. In the case of the GaAs-AlAs systems, this analysis can explain the sharpness of the observed peaks.     

Photon and phonon statistics of Brillouin scattering

The statistical properties for the couples of modes in Brillouin scattering are derived making use of the coherent state technique. Assuming the initial fields to be coherent, it is shown that periodical antibunching, bunching as well as coherent state behaviour can occur, provided that the anti-Stokes interaction prevails. This is demonstrated with the help of the photocount distributions and their reduced factorial moments.Dedicated to Professor Miroslav Trlifaj on the occasion of his sixtieth birthday.Editorial notice: We regret to record the death of Professor Trlifaj on 10. 2. 1982.The authoress would like to express her sincere thanks to Dr. J. Peina for comments and stimulating discussions.     

Brillouin scattering in crystals of γ-oxygen

Brillouin scattering experiments have been performed on a series of 12 independently grown crystals of γ-oxygen. The hypersonic velocities, near the triple point, are almost independent of crystal orientation. Preliminary values of the adiabatic elastic constants at the triple point are c₁₁ = 2.57, c₁₂ = 2.01, and c₄₄ = 0.28 (in units of 10¹⁰ dyn cm^?2).     

Hadron-nucleus scattering as a function of nuclear size

High-energy hadron-nucleus collisions, when viewed in terms of nuclear size, exhibit a remarkable simplicity. The data suggest that nuclear matter is extremely opaque to hadrons, and that fast-forward hadrons (x≳0.3) arise solely from peripheral collisions. This picture naturally explains why the production ratios of different hadron species are target independent at large x.