Brillouin scattering

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

Melting curve and fluid equation of state of carbon dioxide at high pressure and high temperature.

Abstract: The melting curve and fluid equation of state of carbon dioxide have been determined under high pressure in a resistively-heated diamond anvil cell. The melting line was determined from room temperature up to $11.1\pm0.1$~GPa and $800\pm5$~K by visual observation of the solid-fluid equilibrium and in-situ measurements of pressure and temperature. Raman spectroscopy was used to identify the solid phase in equilibrium with the melt, showing that solid I is the stable phase along the melting curve in the probed range. Interferometric and Brillouin scattering experiments were conducted to determine the refractive index and sound velocity of the fluid phase. A dispersion of the sound velocity between ultrasonic and Brillouin frequencies is evidenced and could be reproduced by postulating the presence of a thermal relaxation process. The Brillouin sound velocities were then transformed to thermodynamic values in order to calculate the equation of state of fluid CO$_2$. An analytic formulation of the density with respect to pressure and temperature is proposed, suitable in the $P-T$ range 0.1-8~GPa and 300-700~K and accurate within 2\%. Our results show that the fluid above 500 K is less compressible than predicted from various phenomenological models.

Broad-band transmitted intensity noise induced by Stokes and anti-Stokes Brillouin scattering in single-mode fibers

Abstract: We experimentally investigate the optical noise induced by stimulated Brillouin scattering (SBS) in single-mode fibers. The noise, which is caused by the random nature of spontaneous Brillouin scattering, is induced in the transmitted wave as well as in the backward Brillouin wave. In fibers where the Brillouin gain spectra consist of several resonances, the induced intensity noise of the transmitted wave has a wide spectrum and it may be the dominant noise in the receiver for a broad radio frequency band (0-1 GHz). This unexpected result is explained by a multiple scattering process which is caused by stimulated and by thermally excited phonons. The SBS induced noise may cause a performance degradation in analog optical systems which require high optical powers and low noise. Using fibers with a single Brillouin resonance may limit the noise to lower frequencies.

Studies of molecular relaxation of poly(propylene oxide) solutions by dielectric relaxation and brillouin scattering

Abstract: Dielectric relaxation and Brillouin scattering are jointly used in studying molecular relaxation in poly(propylene oxide) (PPO) and its solutions in methylcyclohexane. The dielectric method was applied to the more concentrated (100%, 80%, 60%, by volume) solutions over a wide temperature and frequency range (30 Hz to 8 GHz) in order that the variation in activation energy characteristic of a glass-forming substance could be delineated. The present work extends previous work on the undiluted polymer to higher frequencies so that range of 12 decades in the dielectric loss maximum fmax as a function of temperature is now available. The “Antoine” equation is found to represent the behavior of log fmax, of the bulk concentrated solutions very well. The more dilute (40%, 20%) solutions were studied only in the high-frequency (GHz) region since phase separation occurred at low temperatures. Both the temperature and dilution effects were interpreted in terms of free-volume theory. Brillouin scattering spectra were obtained at several scattering angles and a wide range of temperatures. A maximum in the curve of hypersonic attenuation versus temperature was observed in each polymer solution. The attenuation maximum shifts toward lower temperature upon dilution, in agreement with the dielectric relaxation result. The Brillouin scattering follows different activation parameters and evidences a more rapid process than does the dielectric relaxation. It is speculated that it monitors a secondary or subglass relaxation, due perhaps, to damped torsional oscillations.

Suppression of brillouin scattering in lightwave transmission system

Abstract: Optical nonlinear effects, such as stimulated (Brillouin) scattering, cause disproportionate attenuation of transmitted optical signals and usually occurs only when the optical power exceeds a certain level. One of the most important types of nonlinear scattering which occurs in an optical fiber as the power of the optical signal is increased above a certain level is stimulated Brillouin scattering. Brillouin scattering limits the power density of an optical signal that can be injected into an optical fiber. This invention suppresses Brillouin scattering and, by so doing, permits the power density of the optical signal which is injected into an optical fiber to be increased approximately threefold before the Brillouin scattering threshold is reached. More specifically, in a lightwave AM-VSB CATV transmission system having an external modulator, the optical beam which is amplitude modulated with the CATV signals is also phase modulated with a sinusoidal signal having a frequency which is not less than twice the frequency of the highest CATV signal. The phase modulation of the optical beam suppress Brillouin scattering. With this invention the power density of the CATV signal can be increased approximately three fold before the threshold of Brillouin scattering is reached.

Stimulated Brillouin scattering for microwave signal modulation depth increase in optical links

Abstract: Carrier reduction from a weakly modulated optical signal is required in highly linear optoelectronic links. The proposed solution uses stimulated Brillouin scattering (SBS) that occurs in optical fibres to deplete the carrier and leave the modulation sidebands unchanged. A modulation depth gain of >20 has been obtained using this method.