Showing papers on "Brillouin scattering published in 1985"

Guided acoustic-wave Brillouin scattering.

Abstract: Forward light scattering by the thermally excited guided acoustic modes of an optical fiber produce numerous narrow lines not predicted by the usual theory of Brillouin scattering. Optical heterodyne detection has been used to resolve the scattering spectrum which begins at about 20 MHz and extends to the detection limit. A simple theory quantitatively accounts for the frequencies, polarizations, and intensities of the components. The light scattering from these modes constitutes a thermal-noise source in optical fibers that may prove significant in other experiments.

Generation and detection of squeezed states of light by nondegenerate four-wave mixing in an optical fiber.

Abstract: Nondegenerate four-wave mixing in a single-mode optical fiber is proposed as a method of squeezed state generation. An analysis of the near-degenerate mixing process for forward propagation in realistic fibers is presented along with the theory of an experimentally feasible detection strategy. The effects of the quantum nature of the optical nonlinearity and absorption are modeled by treating the fiber medium as a collection of anharmonic oscillators. Methods of suppressing undesired effects such as stimulated Brillouin scattering are presented as is a technique for providing the phase-shifted local oscillator wave necessary for the detection of squeezing. Preliminary experiments on fiber characterization and the detection of four-wave parametric fluorescence are described.

Optical phase conjugation by backscattering in barium titanate

Abstract: We demonstrate optical-beam phase conjugation by the process of two-beam coupling in photorefractive barium titanate The incident, image-bearing beam causes exponential gain for counterpropagating waves, which are fed by noise and emerge with a power of the order of 10% of the incident beam and phase conjugate to it This is expected from the calculated plane-wave gain plus the analogy to the theory of phase conjugation of complex wave fronts by stimulated Brillouin backscattering We conjugate beams at either 515 or 488 nm at between 10- and 50-mW power, and find, as expected, no frequency shift (<1 Hz) in the process

Resolved forward Brillouin scattering in optical fibers.

Abstract: Forward light scattering by the thermally excited acoustic eigenmodes of an optical fiber produce numerous narrow lines not predicted by the bulk-interaction theory of Brillouin scattering. Optical heterodyne detection has been used to resolve the scattering spectrum which begins at about 20 MHz and extends to the detection limit.

Steady and relaxation oscillations of stimulated Brillouin scattering in single-mode optical fibers

Abstract: The temporal behavior of stimulated Brillouin scattering (SBS) in single-mode optical fibers is investigated theoretically and experimentally It is shown that if external feedback exists, the SBS and the transmitted pump intensities exhibit steady oscillations with a period of twice the transit time in the fiber However, if the ratio between the SBS intensity and the input intensity is above a certain value, the oscillations decay

Performance of a Nd: YAG oscillator/ampflifier with phase-conjugation via stimulated Brillouin scattering

Abstract: Phase conjugation via stimulated Brillouin scattering in CH4 gas has been used to correct amplifier aberrations in a Nd: YAG oscillator/amplifier system. The single amplifier stage has been used in two-pass and four-pass arrangements. Using the four-pass arrangement incorporating compensation for thermal birefringence, a single-frequency diffraction-limited output of 350 mJ, in a compressed 6 ns pulse is achieved at 15 Hz repetition rate.

Subnanosecond pulses from a KrF laser pumped SF 6 Brillouin amplifier

Abstract: Experimental measurements are presented of pulse compression in a backward Brillouin amplifier using SF 6 gas pumped by 0.9 GHz linewidth KrF laser radiation. Average pulse durations of 390 ps and energy extraction effieiencies of 40 percent from 24 ns pump pulses have been demonstrated at pressures of 15.3 and 12.6 atm, respectively.

Optical phase conjugation

Abstract: The time-reversal of light waves is discussed. Two of the most widely used methods of phase conjugation of light waves, stimulated Brillouin scattering and four-wave mixing, are described. The physical bases of both methods are shown. Two possible applications of optical phase conjugation, the production of highly directed laser beams and the self-targeting of radiation, are discussed.

Coherent optical-fibre subscriber line

Abstract: A laboratory bidirectional four-channel broadband coherent-type fibre-optic subscriber line (3.5 km) is reported. The carriers are centre-frequency-stabilised by a ‘heterodyne spectroscope’ and demultiplexed by a tunable heterodyne receiver. In a very special state of the system, BER increases for nonlinear interaction between two counterpropagating narrowband lightwaves because of Brillouin scattering.

Crosstalk due to stimulated Brillouin scattering in monomode fibre

Abstract: Interactions between two counterpropagating narrowband lightwaves (frequency difference=20 GHz, λ=825 nm) in a monomode optical fibre can occur because of stimulated Brillouin scattering. Maximal signal gain of 10% is obtained for a pump power of 313 μW. The interactions extend over 500 MHz with two resonant frequencies.

Rayleigh–Brillouin scattering studies of segmental fluctuations in poly(siloxanes)

Abstract: New results from a detailed temperature dependent Rayleigh–Brillouin study of siloxane polymers are reported. The study includes the examination of the effect of the relaxation of the longitudinal stress modulus on the propagation behavior of the thermally driven acoustic wave in the 109 Hz frequency range. The Rayleigh–Brillouin spectra of poly(diphenyl siloxane), poly(phenylmethyl siloxane) as well as their model analogs, 1,3‐tetraphenyl 1,3‐dimethyl disiloxane, and 1,3‐diphenyl 1,2‐tetramethyl disiloxane are measured over a wide range of temperature covering from Tg to 240 K above Tg. The theory for Rayleigh–Brillouin scattering has also been reformulated in such a way that the parameters which enter the theory are in terms of easily recognizable thermodynamic and transport coefficients.

Dispersion of localized elastic modes in thin supported gold layers measured by Brillouin scattering

Abstract: The dispersion of higher‐order localized elastic modes of gold layers on glass has been measured by Brillouin scattering. For layer thicknesses h≥100 A the dispersion of the sound velocities is well described by elastic continuum theory, whereas for h<100 A deviations occur due to island formation. The results yield a reliable, nondestructive method to determine either elastic constants and mass density or the thickness of thin supported metal layers.

Radiation pressure on macroscopic bodies

Abstract: The force exerted by a high-frequency electric field on a macroscopic body is calculated. Starting from total momentum conservation, a rigorous definition of radiation force density is given, and the relationship between a time-averaged Maxwellian stress tensor and radiation pressure is clarified. Formulas are presented for calculating the volume force density of the radiation-force term. It is further shown that all resonant wave–wave interactions of nonlinear optics, such as stimulated Brillouin and Raman scattering, are driven by radiation pressure. The limits of validity of the radiation-pressure concept are discussed.

Studies of the rotation-translational coupling and bulk-viscosity relaxation of liquids composed of anisotropic molecules by Rayleigh-Brillouin scattering

Abstract: Effects of the rotation—translational coupling on the spectra of the longitudinal and transverse (sheer) acoustic phonons in molecular liquids have been analysed. Experimental results, supporting theory, are presented. Modern development in optical technology has made the Rayleigh-Brillouin light scattering technique vry useful in studying translation and rotational motions of molecular liquids in the GHz (10 Hz) frequency range. The spectrum in this frequency range consist of a central component and a pair of shifted sidebands. In general , the central Rayleigh components in polarized and depolarized spectrum arise from the overdamped translational and rotational diffusive motion; the shifted sidebands are due to scattering of the incident light from the thermally induced sound waves in the medium. At the 900 scattering angle, the scattered light observed in the polarized (VV) scattering configuration is a superposition of the isotropic (due to density fluctuations) and anisotropic (due to orientational fluctuations) components in the combination: 4 = J50(qw) + Ij(qw) (1) On the other hand, the scattered light observed in the depolarized (VH) scattering configuration is only due to orientational fluctuations: = 'ani' (2) Thus by measuring both the VV and VH scattering spectral components, it is possible to separate the isotropic and anisotropic components from the VV spectrum. Here the quantity q which appears in Eqs. (1) and (2) is equal to , — 4rn . 0 where A is the waveq q1 sin 2' length of the incident light in vacuum, n is the refractiveindex, an.d 0 is the scattering angle. The combination known as the longitudinal stress modulus M(t) + G(t). However, the anisotropic component of the scattering spectrum is closely associated with the relaxation behavior of the shear modulus G. In this paper, we shall give a hydrodynamic description of the effect of the rotation-translational coupling on the spectra of density fluctuations and orientational fluctuations of molecular liquids composed of anisotropic molecules. Experimental results confirming the theory will be presented at the conference. AlthougI nalysis of the experimental spectra was previously provided using microscopic theory, ' we shall present the analysis here using the method of continuum mechanics. This is possible because the fluctuating wavelength involved in light scattering is long compared with the inter-molecular distance. Consider first the general formulation. The intensity distribution of the isotropic component of the dynamic light scattering spectrum detected at the scattering angle 0 is proportional to the Fourier transform of the time correlation function of the density fluctuation C(q,t) given by * C(q,t) = <6p(q,t)6p (s)> (3) where p(q,t) is the spatial Fourier transform of the fluctuation of the number density from the equilibrium value p0 within scattering volume. In continuum mechanics, the connection between force and deformation is formulated in terms of the stress-strain relation (i.e. the constitutive equation). The general constitutive equation for the linear stress-strain relation incorporating the rotation-translation coupling appropriate for describing the light scattering spectrum from an isotropic system 247

Experimental Studies on Mixed Ferro-Antiferroelectric Glasses

Abstract: The growth, structure, and dynamics of RbH2PO4–NH4H2PO4 mixed crystals are reviewed. In the intermediate concentration range, the built-in frustration of these materials prevents the ordinary ferroelectric or antiferroelectric transitions, whereby the disordered acid-proton sublattice freezes into a glass. This has been observed with a number of experimental techniques, including dielectric dispersion, optical birefringence, X-ray diffraction and scattering, Raman and Brillouin scattering, NMR, and more recently, specific-heat and neutron scattering. The variety of techniques applicable to this system has allowed the observation of polarization freezing over about 17 orders of magnitude in frequency. This freezing is well described phenomenologically by the Vogel-Fulcher law, while other laws proposed for spinglasses are less successful. Recent hypersonic-relaxation measurements point to the existence of a frozen polarization component at temperatures already much above Vogel-Fulcher freezing, while neutron diffused scattering reveals that the tendency to form superstructures is not static.

Optical communications systems and process for signal amplification using stimulated brillouin scattering (SBS) and laser utilized in the system

Abstract: Communications Systems particularly suited for manipulating stimulated Brillouin scattering (SBS), or similar tunable laser amplification effects, to acheive improved means for selecting an optical signal from many such signals carried on a single fiber. This disclosure also describes means for producing a tunable, spectrally-narrow line to power this laser amplification. The disclosure also describes an improved polarization-sweeping device which allows the system to handle variable polarization of signals, when necessary. It also discloses other subsystems and apparatus facilitating the optimum signal-tapping process, including heterodyning procedures, a low-band-width channel-indentification means, and a new laser, all particularly useful in the system described. The laser is also useful in other systems where a tunable, spectrally narrow, stable source is required.

Brillouin scattering, two‐plasmon decay, and self‐focusing in underdense ultraviolet laser‐produced plasmas

Abstract: Underdense foam targets were irradiated with a single UV laser beam at intensities up to 1015 W/cm2 The incident laser propagated into the foam a distance of 500–1000 μm, depending on the average target density The backscattered Brillouin and 3ω0/2 radiation were observed to have the same dependence on the incident laser intensity, indicating a strong interrelation of these processes A possible coupling mechanism is proposed

Self-generated loss of coherency in Brillouin scattering and reduction of reflectivity.

Abstract: Low reflectivity of stimulated Brillouin scattering is shown to result from wave-interaction incoherency caused by the ion sound-wave nonlinearity. The Brillouin reflectivity is numerically found to display a chaotic time evolution at laser fluxes below those at which ion sound-wave harmonic generation takes place. At these fluxes, the scattered light exhibits a spiky frequency spectrum. Scaling laws for the reflectivity are given.

Phase conjugation in an optical fibre

Abstract: We report experimental studies of phase conjugation by stimulated Mandelstam Brillouin scattering in multimode fibres. A dramatic decrease in the threshold power as compared to that (104 to 105 W) typically observed in conventional media was achieved. A ruby pulsed pump with ∼ 500-ns pulses was used. For the 7-m-long fibre, the threshold power was ≈ 50 W, the degree of phase conjugation was almost one, the pump-to-Stokes conversion efficiency was about 80%. For the 130-m-long fibre, the threshold power decreased to ≈ 10 W and the pump-to-Stokes conversion efficiency reached 100%. Polarization scrambling was observed in the 130-m-long fibre, but the Stokes wave with polarization coinciding with that of the pump wave was a phase-conjugate replica of the pump, as before.

Brillouin scattering study of multilayer cobalt-niobium films

Abstract: Spin waves which are characteristic of periodic structures of thin ferromagnetic Co films alternating with nonmagnetic Nb films have been investigated by means of Brillouin light scattering. The dependence of the magnon frequencies on the magnetic inplane field and on the wave-vector was measured for several samples with different numbers and thicknesses of the layers. The experimental data are in good agreement with a theory of magnetostatic surface spin waves in such media elaborated by Grunberg and Mika. The amplitudes of the transverse magnetization in the different layers of the stack have been calculated. The highest frequency branch resembles the Damon-Eshbach surface magnon. With decreasing frequency the branches acquire volume mode character. In addition, a number of phonon branches has been observed which are interpreted as plate modes of the combined Co-Nb layer on the Si substrate.

A Soft Acoustic Mode in the Ferroelastic Phase Transition of LaNbO4

Abstract: An anisotropic softening of the acoustic mode in the ferroelastic phase transition of LaNbO 4 has been observed by the Brillouin scattering experiment. The transverse mode propagating along a direction deviated from the crystal axis by 23° in the a b -plane shows a complete softening at the transition temperature T 0 . The direction is parallel or normal to the ferroelastic domain boundary as predicted by the phenomenological analysis of the phase transition from 4/ m to 2/ m symmetry. Thc temperature dependence of the elastic susceptibility is well described by the classical indices γ=γ'=1 in both phases, suggesting a typical proper ferroelastic transition.

Formation of subnanosecond pulses by stimulated Brillouin scattering of radiation from a pulse-periodic YAG:Nd laser

Abstract: An experimental investigation was made of the time profile of Stokes pulses as a function of the energy, repetition frequency, and conditions of focusing of laser pulses in various systems of stimulated Brillouin scattering (STBS) mirrors. Cascade STBS shortening of laser pulses reduced the duration from 12 nsec to less than 0.2 nsec in the case of Stokes pulses.

Simplified technique for subnanosecond pulse generation and injection mode-locking of a XeCl laser

Abstract: A line narrowed XeCl oscillator/amplifier has been used to generate pulses of ≤100 ps duration by a combination of stimulated Brillouin scattering and optical breakdown. In addition, a Brillouin mirror has been used to control the amplified spontaneous emission in an injection mode-locked XeCl oscillator.

Stimulated Brillouin scattering of KrF laser radiation in dichlorodifluoromethane

Abstract: Experimental measurements have been made of the stimulated Brillouin backscatter from CCl 2 F 2 gas in the range of pressures from 1 to 5.75 atm. Using narrow-linewidth KrF laser radiation as the pump backscatter efficiencies of up to 35 percent have been achieved, while at low backscatter efficiencies pulses as short as 1.5 ns in width were obtained.

Brillouin scattering study of the ferroelectric phase transition in tris-sarcosine calcium chloride

Abstract: Brillouin spectra from longitudinal phonons in ferroelectric tris-sarcosine calcium chloride propagating along [100], [010], and [001] have been measured as functions of temperature. Large anomalies were found in the Brillouin shift and hnewidth in the [100] and [001] phonons. These anomalies are interpreted as arising from the linear coupling of the polarization and the phonons. From the temperature where the linewidth is maximum, the relaxation time of the polarization fluctuations is estimated to be ~=3.1X10 ' /(T, — T) sec, where T, is the ferroelectric transition temperature. We also observed anomalies in Brillouin shift and linewidth of the [010] phonons which propagate along the ferroelectric b axis. These anomalies are interpreted as coming from electrostrictive coupling. The energy-relaxation time was estimated to be ~E — 2. 5&(10 ' /(T — T, ) sec in the paraelectric phase and ~E — 1.0& 10 /(T, — T) sec in the ferroelectric phase, by comparing our Brillouin results with those of the ultrasonic measurements.

Single-pulse Raman scattering studies of heterogeneous explosive materials

Abstract: Raman scattering from ambient and shock-loaded heterogeneous (compressed pure polycrystalline) explosive materials has been examined using single-pulse laser excitation. In the case of triamino-trinitrobenzene (TATB), intense nonlinear scattering at 1170 cm−1 has been observed.