Showing papers on "Brillouin scattering published in 1996"

Handbook of Nonlinear Optics

Abstract: Elements of the theory of nonlinear optics frequency doubling and mixing optical parametric generation, amplification, and oscillation characterization of second order nonlinear optical materials properties of selected second order nonlinearoptical materials nonlinear index of refraction characterization of nonlinear refractive index materials optical properties of selected third order nonlinear optics materials nonlinear absorption experimental techniques in nonlinear absorption ultrafast characterization techniques laser flash photolysis nonlinear absorption properties of selected materials stimulated Raman scattering stimulated Brillouin scattering properties of selected stimulated light-scattering materials theelectro-optic effect.

Elastic constants of gallium nitride

Abstract: The elastic constants of GaN have been determined using Brillouin scattering; in GPa they are: C11=390, C33=398, C44=105, C66=123, C12=145, and C13=106. Our values differ substantially from those quoted in the literature which were obtained from the determination of mean square displacement of atoms measured by x‐ray diffraction.

Simple distributed fiber sensor based on Brillouin gain spectrum analysis

Abstract: A novel configuration of a distributed fiber sensor by Brillouin gain analysis has been developed for temperature and strain monitoring. It uses a single laser source, and the required light signals are all generated with an electro-optic modulator, resulting in high stability and excellent reliability of the measuring setup. Measurement of the induced strain in a wound fiber is presented as a demonstration of the system performance.

Distributed sensing technique based on Brillouin optical-fiber frequency-domain analysis.

Abstract: A new sensing technique for the distributed measurement of temperature and strain, based on Brillouin optical frequency-domain analysis, is presented. Theoretical investigations and first experimental results of distributed measurements demonstrate the feasibility of this new concept.

Hybrid Brillouin/erbium fiber laser.

Abstract: We propose and demonstrate a novel hybrid Brillouin/erbium fiber laser that uses both Brillouin gain in single-mode optical fiber and gain in erbium-doped fiber. The lasing frequency was accurately determined by the Brillouin shift in single-mode optical fiber and was 10.35 GHz from the Brillouin pump. Large powers could be extracted because of incorporation of erbium-doped fiber in the laser resonator. An output power of 10 mW was measured at a wavelength of 1532 nm.

SBS threshold of a fiber with a Brillouin frequency shift distribution

Abstract: The SBS threshold of a fiber with Brillouin frequency shift distribution along its length is investigated theoretically and experimentally. We obtain a simple equation for estimating the SBS threshold from the effective gain coefficient, which is calculated by using the Brillouin frequency distribution along its length. The dopant concentration dependence of the Brillouin frequency shift are measured for fibers with an F and GeO/sub 2/ codoped silica core. The evaluated frequency shift per unit of dopant concentration is 277 MHz/wt% and 45 MHz/wt% for F and GeO/sub 2/, respectively, at 1.55 /spl mu/m. The SBS threshold of a fiber with a nonuniform Brillouin frequency shift distribution prepared by the VAD method is investigated experimentally. The fiber exhibits 7 dB improvement in its SBS threshold. This value is in good agreement with one estimated by calculating the effective gain coefficient. This simple equation will be useful for estimating the SBS threshold of various fibers.

Brillouin scattering study in the GaN epitaxial layer

Abstract: We have investigated the elastic properties of a GaN epitaxial layer on a sapphire substrate by Brillouin scattering in the backward and 90° scattering geometries. A sample of high optical quality grown by the two-flow MOCVD method with a complex structure of In 0.05 Ga 0.95 N(0.05 μm)/GaN(2 μm)/sapphire was used. The weak spectra were not simple due to the boundaries and the InGaN thin film. The elastic constants of GaN were estimated and compared with those obtained from X-ray diffraction.

Optical transmitter, optical communication system and optical communication method

Abstract: An optical transmitter comprises a first unit for generating an optical signal having a bandwidth given by a main signal, a second unit modulating the optical signal according to a control signal to extend the bandwidth of the optical signal, a third unit extracting backward light including SBS(stimulated Brillouin scattering) light generated in an optical fiber transmission line, and a fourth unit performing feedback control so that the power of the SBS light becomes substantially constant. Through the structure of the optical transmitter good transmission characteristics of a main signal are obtained and the suppression of the SBS is allowed.

Interaction of crossed laser beams with plasmas

Abstract: The parametric interaction of two crossed collimated laser beams with ion plasma modes has been studied. The underlying process is a density grating that is created by the two laser beams. The Bragg diffraction that is produced enhances forward stimulated Brillouin scattering (SBS) which results in a time dependent energy exchange between the two beams. A diversity of other SBS processes which depend on the symmetry of driving laser beams are also discussed.

Multifrequency lightwave source using phase modulation for suppressing stimulated Brillouin scattering in optical fibres

Abstract: Spectral broadening over a large range using PM (Phase Modulation) is achieved by a lightwave source without the need for a large phase modulation index and without expending a large amount of modulator RF drive power. In this lightwave source, a laser output signal is externally phase modulated by one or more modulation signals. The phase modulation employs one or more frequency drive signals (i.e., the modulation signals) each of whose amplitude is judiciously selected to produce an output spectrum having substantially equal spectral components over a predetermined range of frequencies. The predetermined frequency range is centered about the source frequency for the laser and resembles a comb. Each frequency drive signal is also selected to have a frequency (or frequency spacing from other drive signals) so that adjacent spectral components in the output spectrum of the modulated signal are produced with a frequency spacing which exceeds the SBS (Stimulated Brillouin Scattering) interaction bandwidth at the transmission wavelength of interest.

Effect of stoichiometry on the dynamic mechanical properties of linbo3

Abstract: Acoustic and optic phonons have been measured by Brillouin and Raman spectroscopies in LiNbO3 samples with different stoichiometries. Consequently, the elastic constants have been determined by Brillouin scattering as a function of the stoichiometry. The C44 elastic constant presents, as a function of the stoichiometry, a clear minimum for the [Li]/[Nb]=1 in the melt sample. This behavior must be related to the existence and competition of two kind of defects, i.e., extended defects induced when growing samples not at the congruent composition, and point defects present in nonstoichiometric samples. The optic phonons seem to be dominated by the point defects. The linear increase of the phonon lifetimes, with respect to an ideal stoichiometric sample, can be due to the scattering by the static imperfections and to an increase of the anharmonic scattering. Several Raman peaks, which appear when the [Li]/[Nb] ratio decreases, are related to the presence of Nb in antisites. The width of some particular phonon...

Performance of strain-free stimulated Brillouin scattering suppression fiber

Abstract: We have investigated experimentally the performance of an SBS suppression fiber with a nonuniform dopant concentration along its length fabricated by the VAD method. We have achieved an SBS threshold of 15 dBm against a continuous wave at 1.55 /spl mu/m. This is 7 dB larger than that of conventional fiber. We have confirmed experimentally that the increase in the SBS threshold can be estimated from the ratio of the Brillouin frequency shift change over the effective interaction length to the intrinsic Brillouin gain bandwidth. Moreover, we have confirmed that there is no BER degradation after a transmission of 138 km through a 2.5 Gb/s intensity modulation direct detection system when the SBS suppression fiber is used with an input power of 16 dBm.

Effective suppression of amplified spontaneous emission by stimulated Brillouin scattering phase conjugation

Abstract: Backward stimulated Brillouin scattering was used to control the growth of amplified spontaneous emission (ASE), reducing the unwanted emission in a pulse-amplified cw Ti:sapphire laser system from 22% to less than 1 × 10−4 in the final output. Suppression of ASE substantially improved the spectral quality of the laser and broadened the range over which the laser is useful. The output duration was compressed, but the pulse remained nearly transform limited.

Performance of S train-Free S tirnulated Brillouin Scattering Suppression Fiber

Abstract: Abstruct- We have investigated experimentally the performance of an SBS suppression fiber with a nonuniform dopant concentration along its length fabricated by the VAD method. We have achieved an SBS threshold of 15 dBm against a continuous wave at 1.55 pm. This is 7 dB larger than that of conventional fiber. We have confirmed experimentally that the increase in the SBS threshold can be estimated from the ratio of the Brillouin frequency shift change over the effective interaction length to the intrinsic Brillouin gain bandwidth. Moreover, we have confirmed that there is no BER degradation after a transmission of 138 km through a 2.5 Gbls intensity modulation direct detection system when the SBS suppression fiber is used with an input power of 16 dBm.

Technique for measurement of the Raman gain coefficient in optical fibers.

Abstract: We demonstrate a simple, novel technique for measurement of the Raman gain spectrum in optical fibers. We measure the stimulated Raman scattered power generated by a square pulse as a function of its pulse width. Because of fiber dispersion, increasing the pulse width increases the interaction length of the pump and Stokes pulses and leads to a higher Stokes power. The dependence of growth rate of Stokes power on pulse width gives the Raman gain coefficient. Our technique does not require calibration against a standard or absolute measurement of the Stokes signal. We show that gain values obtained with this technique agree well with direct pump-probe measurements.

The Raman Effect

Abstract: Publisher Summary This chapter discusses the Raman effect which results from the interaction of vibrational and rotational motions of molecules with electromagnetic radiation. Brillouin scattering involves the translational motion of molecules in liquids and solids. A simple classical picture of the Raman effect can be obtained by analogy with the amplitude modulation of a radiofrequency carrier wave by an audio signal. The resulting sidebands are similar to the Raman spectrum produced by the combination of the frequencies of molecular vibrations with the frequency of the laser excitation. However, for most purposes, a quantum mechanical model is more useful. The interaction of a molecule with electromagnetic radiation can thus be analyzed in terms of an energy-transfer mechanism. The simplest absorption process involves the gain of a quantum of energy by the molecule, accompanied by the annihilation of a quantum of light or photon. Similarly, spontaneous emission can be described as the creation of one or more photons due to the corresponding loss in molecular energy. The “excitation profile” in resonance Raman spectroscopy describes the intensity of Raman scattering as a function of the frequency of the excitation.

Modeling of a stimulated Brillouin scattering experiment with statistical distribution of speckles

Abstract: The results of experimental studies of stimulated Brillouin scattering (SBS) from a laser beam smoothed with a random phase plate (RPP) in a preformed expanding plasma are compared with the statistical theory of SBS from an inhomogeneous plasma. Many observed features can be explained assuming that SBS occurs in randomly distributed speckles. This hypothesis naturally combines observed pump depletion effects within a speckle, with relatively minor SBS reflectivity of the whole interaction beam.

Effects of plasma long‐wavelength hydrodynamical fluctuations on stimulated Brillouin scattering

Abstract: Two important effects of long wavelength velocity and density perturbations on stimulated Brillouin scattering (SBS) have been identified: (i) nonlinear interaction of the SBS‐produced ion acoustic wave with velocity perturbations provides detuning of the SBS interaction, formation of ion acoustic wave satellites and its additional damping; (ii) harmonic generation of long wavelength density perturbations enhances the spectral density of ion acoustic fluctuations over a wide range of wavevectors, including SBS resonant sound waves. The first effect reduces the magnitude of the SBS gain, and the second one enhances the nonthermal noise level for SBS. Long wavelength ion acoustic perturbations reduce SBS reflectivity more dramatically than short wavelength harmonics produced by the SBS driven nonlinear sound wave.

Method for making Ge-Doped optical fibers having reduced brillouin scattering

Abstract: In accordance with the invention, a Ge-doped optical fiber having reduced Brillouin scattering loss is made by modulating the tension applied to the fiber during draw. The draw tension is modulated between a low range 10-50 g and a high in the range 150-250 g. The result is SBS suppression with no significant change to end-to-end fiber loss or dispersion factors.

Dependence of stimulated Brillouin scattering on laser intensity, laser f number, and ion species in hohlraum plasmas.

Abstract: Stimulated Brillouin scattering has been studied in plasma conditions approaching those expected within laser-driven cavities (hohlraums) capable of driving a fusion capsule to ignition with x rays. These conditions are achieved using a gas-filled hohlraum design that was fielded at the Nova laser. As the intensity of an interaction beam (351 nm in wavelength) is increased above an onset value {ital I}{sub {ital c}}, the measured Brillouin backscatter into the lens rises sharply and saturates. {ital I}{sub {ital c}} decreases as the optic {ital f} number increases. The saturation level depends on the gas ion species. {copyright} {ital 1996 The American Physical Society.}

Resonant Seeding of Stimulated Brillouin Scattering by Crossing Laser Beams.

Abstract: This Letter presents the first experimental evidence of seeding of ion acoustic waves (IAW) from stimulated Brillouin scattering along the resonant direction between two interaction beams. Using a secondary interaction beam at a reduced intensity acting as seed, a well defined resonance was observed along the bisecting direction between the two laser beams. A strong reduction of the IAW was observed along off-resonance directions, including for backscatter of the primary beam.

Elastic properties of silicate melts up to 2350 K from Brillouin scattering

Abstract: Compressional wave velocities (Vp) have been determined up to 2350 K on CaSiO3, MgSiO3, CaMgSi2O6, CaAl2Si2O8 and Ca3Al2Si3O12 glasses and melts from Brillouin-scattering experiments made with a 180° backscattering geometry. At the glass transition, the decrease of Vp with increasing temperatures becomes much stronger and the width of the Brillouin lines begins to increase markedly. At the highest temperatures investigated, Vp is similar to the relaxed values determined in acoustic measurements for several of these melts. This indicates that the configurational degrees of freedom of these liquids have become accessible within the very short timescale of Brillouin scattering experiments: equilibrium compressibilities of silicate melts can thus be determined with this technique. Our measurements also suggest that the shear modulus at infinite frequency of silicate melts could vary with either temperature or composition more strongly than assumed currently.

Stimulated Brillouin scattering suppression with low residual AM using a novel temperature wavelength-dithered DFB laser diode

Abstract: The effective threshold for stimulated Brillouin scattering for a data-encoded signal is increased from 11.0 to 23.4 dBm by using a temperature-tunable laser diode. A 5 kHz sinusoid is applied to a Ti/Pt thin film resistor located along the laser contact on top of the device, resulting in a 10 kHz dithering of the wavelength. The residual amplitude modulation index at 10 kHz is only 1.2/spl times/10/sup -4/.

Stimulated Brillouin scattering in the strong coupling regime

Abstract: Stimulated Brillouin scattering (SBS) has been reexamined in the strong coupling limit. The three‐wave interaction in the strong coupling regime, which gives rise to a purely growing mode for wave numbers k≳2k0, where k0 is the wave vector of the pump wave, has been studied. This regime was first found by Cohen and Max [Phys. Fluids 22, 1121 (1979)]. In this regime, for a flowing plasma, a significant portion of the unstable spectrum is found to be blueshifted even for the Mach number equal to unity. For the inhomogeneous case, the convective gain in the strong coupling limit turns out to be identical to the gain in the SBS in the weak coupling limit regime.

Dynamics in condensed molecular systems studied by incoherent light

Abstract: Applications of incoherent light techniques to time-resolved studies in condensed matter are reviewed. Vibrational dephasing ofβ-carotene and a heptamethine dye was studied by interferometric coherent anti-Stokes Raman scattering in solution revealing dephasing times between 300 fs and 1.1 ps. This technique gives results that are analogos to spectral methods, but vibrational frequencies can be determined more precisely. Electronic dephasing was studied for a variety of dyes. Forced light scattering is used to measure the initial evolution of the lineshape functiong(t) up to about 50 fs. In the lowest order approximation,g(t) =Δ 2 t 2 /2,, the dephasing is characterized by a modulation strengthΔ = 25 to 150 THz depending on the dye, the solvent and its temperature, and the pump laser wavelength. Interestingly, the modulation decreases for heptamethine in the long-wavelength tail of the absorption band. Brillouin scattering gives rise to finite dephasing times of neat solvents in forced light scattering.

Low-frequency light-scattering spectroscopy of powders

Abstract: Light-scattering spectra of powders of transparent materials were found to exhibit a characteristic band at frequencies below ∼1 cm−1. This band was observed in all powdered materials studied, including enzymes, organic and inorganic crystals, and glass. We interpret the band as a superposition of Brillouin lines produced in combined elastic and inelastic scattering events. A theoretical expression is deduced for the spectrum that is in good agreement with the experiments.

Phase conjugation in magnetized semiconductors by stimulated Brillouin scattering

Abstract: Based upon the density matrix formulations of nonlinear optical susceptibility, optical phase conjugation via stimulated Brillouin scattering (OPC-SPS) in the presence of a moderately high magnetostatic field is studied in centrosymmetric semiconducting crystals under a parabolic approximation. The magnetostatic field B has a twofold contribution to the coherent radiation - semiconductor interaction through the formation of discrete Landau levels and the sharpening of the density-of-states. Numerical estimations made for an InSb sample at low temperature irradiated by a 5.5 to 6.0 m CO laser reveal enhancement in the value of Brillouin susceptibility in the presence of the magnetostatic field B. This in turn lowers the threshold intensity required for the onset of OPC-SBS. A considerably high reflectivity is obtained when B is increased from 1 to 4.02 T. For experimental observation of OPC-SBS as described in the paper, it may be stressed that the polarization of the laser should be properly determined so that the crystal is effectively centrosymmetric.

Quick Measurement of Brillouin Spectra of Glass-Forming Material Trimethylene Glycol by Angular Dispersion-Type Fabry-Perot Interferometer System.

Abstract: Brillouin scattering of Trimethylene Glycol which often crystallizes on slow cooling was measured from 197 K to 426 K using the angular dispersion-type Fabry-Perot interferometer with a CCD detector. Especially the Brillouin spectra on the cooling from 300 K to 197 K could be observed only in 1.5 h without crystallization. The observed sound velocity and anomalous attenuation are analyzed by a single relaxation model. The relaxation frequency obeys the Arrhenius law with an activation energy of 3.71 kcal/mol. This suggests that the observed sound anomaly is due to the fast β-relaxation process.

Diode-pumped Landau-Placzek based distributed temperature sensor utilising an all-fibre Mach-Zehnder interferometer

Abstract: A Mach-Zehnder interferometer has been used for the first time in the detection system of a distributed temperature sensor, based on the Landau-Placzek ratio method The interferometer separates the back-scattered Rayleigh and Brillouin signals with very low losses Used together with a novel diode-pumped Q-switched fibre laser source, performance has been improved at a substantial cost saving over previously reported work