Showing papers on "Brillouin scattering published in 1995"
TL;DR: In this article, a distributed strain and temperature sensing technique that uses Brillouin scattering in single-mode optical fibers is presented, which is based on strain- and temperature-induced changes in the frequency shift.
Abstract: This paper reviews the developments of a distributed strain and temperature sensing technique that uses Brillouin scattering in single-mode optical fibers. This technique is based on strain- and temperature-induced changes in the Brillouin frequency shift. Several approaches for measuring the weak Brillouin line are compared. >
685 citations
TL;DR: In this paper, a theoretical model of the interaction of the pulsed and CW beams is described and compared with experiments, and issues related to the variation within the sensing fiber of the polarizations of the two beams are investigated.
Abstract: Results are reported from recent research on the use of the Brillouin gain/loss mechanism for distributed sensing. A theoretical model of the interaction of the pulsed and CW beams is described and compared with experiments. Results from a system with a 51 km sensing length are presented. We finally investigate issues related to the variation within the sensing fiber of the polarizations of the two beams. >
302 citations
TL;DR: In this article, the core radius is made non-uniform along its length to utilize the core-radius dependence of the longitudinal acoustic frequency, and the effective Brillouin gain of an SBS suppression fiber prepared by the VAD method was reduced by 3.5 dB compared with conventional fibres.
Abstract: Stimulated Brillouin scattering (SBS) in a fibre is suppressed by making the core radius nonuniform along its length to utilise the core-radius dependence of the longitudinal acoustic frequency. The effective Brillouin gain of an SBS suppression fibre prepared by the VAD method was reduced by 3.5 dB compared with conventional fibres.
152 citations
TL;DR: In this article, the design and operation of a Nd:glass regenerative amplifier using a stimulated Brillouin scattering (SBS) phase conjugate mirror is presented.
Abstract: The design and operation of a Nd:glass regenerative amplifier using a stimulated Brillouin scattering (SBS) phase conjugate mirror is presented. The system can be operated at 25-30 J per pulse with a pulse width of 14 ns and a pulse repetition frequency (PRF) of 6 Hz. This results in an average output power of >150 W with a peak power of 2 GW. The experimentally measured divergence of the amplifier output is 1.25/spl times/ the diffraction limit and it can be frequency doubled with >80% efficiency. The detailed considerations required for this specific amplifier design are discussed as well as how these considerations apply to the design of high average power, high beam quality laser systems in general. >
124 citations
97 citations
TL;DR: A cubic-tetragonal-trigonal sequence of phase transitions in the relaxor ferroelectric Na& &~Bi & ~&Ti03 (NBT) has been studied by Brillouin scattering andounced anomalies for both the hypersonic velocity and damping have been found that peak just between two phase transitions.
Abstract: A cubic-tetragonal-trigonal sequence of phase transitions in the relaxor ferroelectric Na& &~Bi & ~&Ti03 (NBT) has been studied by Brillouin scattering. Pronounced anomalies for both the hypersonic velocity and damping have been found that peak just between two phase transitions in contrast to the ordinary well-known behavior with anomalies in the vicinity of every transition point. The fact that these anomalies are centered in the intertransition region and extend beyond both transitions is attributed to the fluctuations of two coupled order parameters associated with disorder in the Naand Bi-cation distribution in a manner characteristic of relaxor ferroelectrics. Such a phenomenon seems to be typical of relaxor materials and to be the basis of the difFuse phase-transition dynamics.
94 citations
TL;DR: In this article, a scanning interference pattern produced by intersecting two cw lasers generates the density variation (acoustic phonons) through the thermal expansion for a light absorbing liquid.
Abstract: We have developed a new method of phonon spectroscopy using forced Brillouin scattering: A scanning interference pattern produced by intersecting two cw lasers generates the density variation (acoustic phonons) through the thermal expansion for a light-absorbing liquid. When the dispersion relation of phonons is satisfied, phonons are generated resonantly in the liquid. Continuous tuning of the frequency difference between the two lasers enables us to measure a resonance spectrum of light-excited phonons using light scattering phenomena. We demonstrate that this resonance spectrum is equivalent to the Brillouin spectrum of thermal phonons both experimentally and theoretically.
93 citations
TL;DR: The stimulated Raman gain spectrum of optical fibers has been measured down to 6 cm(-1) by means of short pulses and spectral oscillations arising from a Brillouin mediated coupling between cw and pulsed light are observed.
Abstract: The stimulated Raman gain spectrum of optical fibers has been measured down to 6 cm(-1) by means of short pulses. Results for parallel and perpendicular polarizations are reported. With this technique, we observe spectral oscillations arising from a Brillouin mediated coupling between cw and pulsed light.
92 citations
TL;DR: In this article, a solution to the linearized hydrodynamic equations is developed to model the dynamics of the thermal grating, including the effects of finite-rate energy deposition, damping by viscosity and thermal conduction, mass diffusion of the excited-state grating and electrostrictive compression.
Abstract: The nature of optical scattering from laser-induced thermal gratings created in the gas phase is investigated. Thermal gratings are produced with the illumination geometry used to perform degenerate four-wave mixing (DFWM) measurements. Such scattering from thermal gratings can act as a phase-matched interference signal. A solution to the linearized hydrodynamic equations is developed to model the dynamics of the thermal grating. Predictions of this model that uses realistic gas properties are shown to compare favorably with laboratory measurements. The model includes the effects of finite-rate energy deposition, damping by viscosity and thermal conduction, mass diffusion of the excited-state grating, and electrostrictive compression.
69 citations
TL;DR: In this paper, the Brillouin light scattering technique was successfully applied for determining the five effective elastic constants of a single transparent film of hexagonal symmetry, in the micron range of thicknesses.
Abstract: In this work it is shown that the Brillouin light scattering technique can be successfully applied for determining the five effective elastic constants of a single transparent film of hexagonal symmetry, in the micron range of thicknesses. Measurements have been performed on a polycrystalline ZnO film, about 1.3 mu m thick, supported by a Si substrate. A major result of this work is that the elastic constant c66 is selectively determined for the first time from detection of the shear horizontal mode travelling parallel to the film surface. Similarly, a selective determination of c11 is attained from observation of the longitudinal mode guided by the film. The three remaining elastic constants, namely c13, c33, and c44, can be then obtained from detection of the Rayleigh surface mode and of the longitudinal bulk wave propagating at different angles from the surface normal.
65 citations
01 Jan 1995
TL;DR: Brillouin light scattering is generally referred to as the inelastic scattering of an incident optical wave field by thermally excited elastic waves (elastic waves of thermal origin are usually called acoustic phonons) in a sample as mentioned in this paper.
Abstract: Brillouin light scattering is generally referred to as the inelastic scattering of an incident optical wave field by thermally excited elastic waves (elastic waves of thermal origin are usually called acoustic phonons) in a sample. This subject was first investigated early in the century by Brillouin(1) and Mandelshtam(2) in the case of scattering from transparent materials. Since the advent of the laser as a powerful source of monochromatic light, Brillouin scattering has received considerable interest for characterizing elastic and optoelastic bulk properties of materials.3,4 More recently with the introduction of high-contrast spectrometers,(5) scattering from opaque materials can be studied, thereby permitting considerable advances in the study of surface acoustic waves in solids. In the last decade, Brillouin scattering from surfaces, more often called surface Brillouin scattering (SBS), has been widely used to investigate elastic properties of thin films, interfaces, and layered materials.
Patent•
10 Feb 1995TL;DR: In this article, the authors used an intensity modulator in the optical loop of a Brillouin fiber optic gyroscope to attenuate the counterpropagation of the counter-propagating light wave.
Abstract: A Brillouin fiber optic gyroscope includes an intensity modulator in the optical loop which periodically attenuates the Brillouin light waves counterpropagating in the optical loop so that the counterpropagating Brillouin waves each propagate as square waves. The use of square wave modulation for the counterpropagating light wave reduces the cross-effect of the Brillouin waves to substantially the same magnitude as the self-effect so that the non-reciprocal Kerr effect is substantially reduced or eliminated. In order to support the counterpropagating square waves, the optical loop is pumped with pump light having frequency components selected to pump the optical fiber to provide Brillouin light at frequencies necessary to generate square waves in the counterpropagating Brillouin light waves. In addition, the Brillouin light must be generated at the correct intensity and phase relationship to form the square wave. Because the relationship between the pump light and the generated Brillouin light is a non-linear function, the relative magnitudes of the frequency components of the pump light are selected to be different from the relative magnitudes of the Brillouin light so that when the pump light is applied to the optical loop, the transfer function results in the correct magnitudes for the frequency components of the Brillouin light. The intensity modulator assures that the Brillouin light is maintained in the proper phase relationship to maintain a square waveform.
TL;DR: Three-dimensional simulations are presented which calculate the time-dependent, self-consistent evolution of filamentation and stimulated Brillouin backscatter in nonuniform laser beams with intense hot spots.
Abstract: Three-dimensional simulations are presented which calculate the time-dependent, self-consistent evolution of filamentation and stimulated Brillouin backscatter (SBBS) in nonuniform laser beams with intense hot spots. The simulations show significant reflectivity ( $g$1%) for modest average-intensity gain exponents (5--10). Many hot spots cooperate to produce a total SBBS amplification that increases with the plasma length as well as hot-spot length. Temporal beam smoothing with bandwidth comparable to the SBBS growth rate substantially reduces the nonuniform-laser-beam reflectivity.
TL;DR: In this paper, the authors describe a solid-state master oscillator-amplifier-laser (MOPA) with a minimum number of elements for the double-pass single-rod amplifier.
Abstract: We describe a solid-state master oscillator-amplifier-laser (MOPA) with a minimum number of elements for the double-pass single-rod amplifier. It produces 100-W average output power of pulsed light with an almost diffraction limited beam. The Q-switched system works with an average repetition rate of about 3 kHz and the pulse width was 70 ns. As active material we used Nd:YALO (Nd:YAP) which has negligible depolarization. The strong thermal lens of the material with focal lengths of less than 15 cm at pump powers of 8 kW was compensated by a phase conjugating mirror based on stimulated Brillouin scattering (SBS). Therefore, the output power could be varied from 2 W up to 100 W without changing the transversal beam profile. The total efficiency of the amplifier including the phase conjugator is 1.25%. >
TL;DR: The oscillatory behavior of the interlayer exchange interaction is observed in Co/Au/Co sandwiches; the measured values of the pseudoperiod and of the attenuation length agree well with recent determination by magneto-optical and magnetoresistive measurements and with theoretical predictions.
Abstract: Magnetic anisotropies and interlayer exchange interaction are derived from Brillouin-scattering spectra of various thin films with one or two Co magnetic layers, evaporated in ultrahigh vacuum. The oscillatory behavior of the interlayer exchange interaction is observed in Co/Au/Co sandwiches; the measured values of the pseudoperiod (9.6 \AA{}) and of the attenuation length (12 \AA{}) agree well with recent determination by magneto-optical and magnetoresistive measurements and with theoretical predictions.
TL;DR: In this paper, a simple model defines an effective steady SBS gain, and may explain the dispersion of available measured values, as well as a reduction of the overall SBS gains.
Abstract: Transverse material inhomogeneities yielding the guiding properties of any optical fibre also cause a variation of stimulated Brillouin resonance frequency, and thus a spectral broadening as well as a reduction of the overall SBS gain. A simple model defines an effective steady SBS gain, and may explain the dispersion of available measured values.
TL;DR: In this article, theoretical and experimental results on three main effects determining the frequency stability of a Brillouin fiber ring laser, namely, the temperature effects and the nonlinear Kerr and frequency pulling effects are presented.
Abstract: This study shows theoretical and experimental results on three main effects determining the frequency stability of a Brillouin fiber ring laser, namely: the temperature effects and the nonlinear Kerr and frequency pulling effects. The oscillation frequency in a Brillouin fiber ring laser is determined mainly by the axial mode of the cold resonator located under the Brillouin gain curve that experiences the highest gain. This oscillation frequency is therefore temperature dependent since both the free spectral range (FSR) and the gain curve center depend on the temperature. The FSR variation gives rise to a continuous lasing frequency variation while the gain curve shift leads to mode hopping. In addition to these temperature effects, the nonlinear Kerr effect and the mode pulling effect will also slightly shift the lasing frequency away from the resonant frequency of the cold resonator. The Kerr effect depends only on the pump power, while the mode pulling effect depends on both the pump power and the relative location between the lasing mode and the gain curve center. The results of this study are useful in many BFRL applications such as Brillouin fiber-optic gyroscopes, microwave generators and frequency shifters. >
TL;DR: In this paper, the longitudinal and transverse Brillouin spectra along phonon direction have been measured as a function of temperature (50-475 K) in singlecrystal PbMg1/3Nb2/3O3 with scattering angles θs=180° and 32.5±0.2°.
Abstract: The longitudinal (LA) and transverse (TA) Brillouin spectra along [001] phonon direction have been measured as a function of temperature (50–475 K) in single‐crystal PbMg1/3Nb2/3O3 with scattering angles θs=180° and 32.5±0.2°. The Brillouin frequency shift with decreasing temperature shows a broad softening anomaly for both LA and TA phonon modes. For θs=180°, a gradual growth in damping with maximum near 270 K is observed and is attributed to order parameter fluctuations. An additional Landau–Khalatnikov maximum is also observed at Tc∼212 K. This anomaly implies a rapid growth of ferroelectric ordering near Tc and is consistent with the earlier linear birefringence results reported by Westphal et al. The elastic stiffness and compliance constants, CE11, CE44, and sE44 are also determined between 200 and 370 K.
TL;DR: Using a fiber-optic stimulated-Brillouin-scattering amplifier as an active filter, optical clock recovery from 5-Gbit/s return-to-zero-format optical data is demonstrated.
Abstract: Using a fiber-optic stimulated-Brillouin-scattering amplifier as an active filter, we have demonstrated optical clock recovery from 5-Gbit/s return-to-zero-format optical data. Definite patterns and pseudorandom bit sequences were tested. This scheme requires no prior knowledge of the clock frequency and is well suited for operation at higher data rates.
TL;DR: In this article, the authors proposed the possibility of soliton-type pulse propagation in an optical guide with two-level resonant impurities and high-order effects like: higher-order dispersion, self-steepening, stimulated Raman scattering and stimulated Brillouin scattering.
Abstract: We propose the possibility of soliton-type pulse propagation in an optical guide with two-level resonant impurities and high-order effects like: higher-order dispersion, self-steepening, stimulated Raman scattering and stimulated Brillouin scattering. To establish the above results we apply the Painleve singularity structure analysis and find that the system of equations admits the Painleve property only for certain values of the physical parameters involved in the system. The Lax pair of the system equation is explicitly shown. As the system without resonant impurities admits solitons, this system is also expected to admit the remarkable solitons property.
TL;DR: The anisotropy of the speeds of sound is reported for the incommensurate heptadecane/urea inclusion compound as measured by Brillouin scattering, showing the presence of a fourth sound velocity, corresponding to the so-called sliding mode (phason).
Abstract: The anisotropy of the speeds of sound is reported for the incommensurate heptadecane/urea inclusion compound as measured by Brillouin scattering. In addition to the three normal acoustic modes, the results show the presence of a fourth sound velocity, corresponding to the so-called sliding mode (phason). A simple model for the elasticity of incommensurate crystals is used to discuss the polarizations of the sliding mode and the other acoustic modes.
TL;DR: In this article, the authors describe the nonlinear behavior of stimulated Raman scattering (SRS) in a finite homogeneous plasma slab and investigate the enhancement of secondary scattering processes due to the non-linear SRS saturation.
Abstract: Theoretical and numerical calculations are performed using the system of Zakharov and electromagnetic wave equations, to describe the nonlinear behavior of stimulated Raman scattering (SRS) in a finite homogeneous plasma slab. The enhancement of secondary scattering processes due to the nonlinear SRS saturation is investigated. The parametric decay of the resonantly driven Langmuir wave provides a mechanism which saturates SRS and greatly broadens the Langmuir and ion acoustic wave spectra. These enhanced electrostatic fluctuations scatter the incident electromagnetic radiation. Scaling laws for enhanced Brillouin, forward Raman, and anti‐Stokes forward and backward Raman scattering as well as criteria for their strong enhancement are given. The frequency spectra of enhanced Brillouin scattering shows red‐ and blue‐shifted components, with different amplitudes depending on the plasma density and laser intensity. The numerical results have been compared with experimental data providing new or alternative e...
TL;DR: The role of spontaneous scattering and nonlinear refraction on the nonlinear dynamics of stimulated Brillouin scattering with feedback is investigated and feedback suppresses stochasticity in the amplification process of the Stokes emission, giving rise to deterministic behavior.
Abstract: The role of spontaneous scattering and nonlinear refraction on the nonlinear dynamics of stimulated Brillouin scattering with feedback is investigated. We find that feedback suppresses stochasticity in the amplification process of the Stokes emission, giving rise to deterministic behavior, the forms of which are found to be critically dependent on the strength of the nonlinear refraction, which is shown to depend on the polarization-preserving properties of the medium. Our results provide an explanation of the chaotic dynamics observed in polarization scrambled fibers and also account for the simpler forms of dynamical behavior reported using polarization-preserving fibers.
TL;DR: In this paper, the angular dispersion of the velocity of the surface acoustic phonons in the (100)-oriented plane allowed us to calculate the whole elastic tensors (C 11, C 44 and C 12 ) and Poisson's ratio.
TL;DR: In this paper, the authors reported the first demonstration of atmospheric compensation at extended ranges by stimulated Brillouin-scattering phase conjugation at a 2.5m height above ground.
Abstract: We report the first demonstration to our knowledge of atmospheric compensation at extended ranges by stimulated Brillouin-scattering phase conjugation. With a field-of-view aperture product of 175 mm mrad, we studied horizontal ranges up to 6 km at a 2.5-m height above ground, with the refractive-index structure parameter Cn2 as large as 10−13 m−2/3. Compensation was achieved at all ranges, consistent with the turbulence-resolution capability of the 10-cm system aperture. The system was driven by frequency-doubled Nd:YAG lasers operating with ~10-ns pulses that were Raman shifted in gaseous hydrogen to the 683-nm operating wavelength. Raman amplification overcame as much as 85 dB of range and internal losses.
TL;DR: In this article, the stimulated Brillouin scattering (SBS) backscatter from large scale-length gas-filled targets has been measured on the Nova laser, and the results showed that the SBS was <3% for conditions similar to ignition target designs.
Abstract: Stimulated Brillouin backscatter from large scale‐length gas‐filled targets has been measured on the Nova laser. These targets were designed to approximate conditions in indirect drive ignition target designs in underdense plasma electron density (ne∼1021/cm3), temperature (Te≳3 keV), and gradient scale lengths (Ln∼2 mm, Lv≳6 mm) as well as calculated gain for stimulated Brillouin scattering (SBS). The targets used in these experiments were gas‐filled balloons with polyimide walls (gasbags) and gas‐filled hohlraums. Detailed characterization using x‐ray imaging and x‐ray and optical spectroscopy verifies that the calculated plasma conditions are achieved. Time‐resolved SBS backscatter from these targets is <3% for conditions similar to ignition target designs.
TL;DR: In this paper, it was shown that for PANDA fibers both the TR2m modes and the R0m modes induce polarized GAWBS in the low-frequency region.
Abstract: Guided acoustic-wave Brillouin scattering (GAWBS) in PANDA fibers has been investigated experimentally. It is shown that for PANDA fibers both the TR2m modes and the R0m modes induce polarized GAWBS in the low-frequency region. Theoretical calculations agree with the observed frequency shifts of the depolarized GAWBS that are due to the TR2m modes from the polarized GAWBS.
TL;DR: In this article, the Brillouin scattering spectra of poly-Nisopropylacrylamide (NIPA) gels swollen to equilibrium in water were measured as a function of temperature both in the swollen and the shrunken phases.
Abstract: Brillouin scattering spectra of poly-N-isopropylacrylamide (NIPA) gels swollen to equilibrium in water were measured as a function of temperature both in the swollen and the shrunken phases. This is the first Brillouin scattering experiment on a gel undergoing a volume phase transition. At the discontinuous volume phase transition occuring at 33.6° C, large changes were observed in both of the Brillouin shift and the spectral width. From the measured spectra and the temperature-dependent refractive index of the gel, the hypersonic velocity and the attenuation were determined as a function of temperature. The results are analyzed in terms of the nature of sound propagation in gels, structure of the shrunken phase, relaxation processes of the network and solvent, and a role played by water molecules at the phase transition.
TL;DR: A new scheme is proposed for sensing distributed strain and temperature in optical fibers that uses Brillouin scattering as the sensing mechanism and a branched optical fiber network as the sensed fibers.
Abstract: A new scheme is proposed for sensing distributed strain and temperature in optical fibers. This scheme uses Brillouin scattering as the sensing mechanism and a branched optical fiber network as the sensing fibers. Brillouin optical time-domain reflectometry makes it possible to distinguish Brillouin-scattered light waves from different optical fiber branches in the network when the different Brillouin frequency shifts are assigned to each branch. The technical feasibility of this scheme is confirmed experimentally for a branched optical network composed of two branches connected to a trunk optical fiber.