The co-existence of the Raman and Brillouin backscattering instability is an important issue for inertial confinement fusion. The present paper presents extensive one-dimensional(1D) particle-in-cell(PIC) simulations ...The co-existence of the Raman and Brillouin backscattering instability is an important issue for inertial confinement fusion. The present paper presents extensive one-dimensional(1D) particle-in-cell(PIC) simulations for a wide range of parameters extending and complementing previous findings. PIC simulations show that the scenario of reflectivity evolution and saturation is very sensitive to the temperatures, intensities, size of plasma and boundary conditions employed. The Langmuir decay instability is observed for rather small k_(epw)λ_D but has no influence on the saturation of Brillouin backscattering, although there is a clear correlation of Langmuir decay instability modes and ion-fractional decay for certain parameter ranges. Raman backscattering appears at any intensity and temperature but is only a transient phenomenon. In several configurations forward as well as backward Raman scattering is observed. For the intensities considered, I λ_o^2 above 10^(15) W μm^2/cm^2, Raman is always of bursty nature. A particular setup allows the simulation of multi-speckle aspects in which case it is found that Raman is self-limiting due to strong modifications of the distribution function. Kinetic effects are of prime importance for Raman backscattering at high temperatures. No unique scenario for the saturation of Raman scattering or Raman–Brillouin competition does exist. The main effect in the considered parameter range is pump depletion because of large Brillouin backscattering. However, in the low k_(epw)λ_D regime the presence of ion-acoustic waves due to the Langmuir decay instability from the Raman created electron plasma waves can seed the ion-fractional decay and affect the Brillouin saturation.展开更多
Backscattered lightwaves from an optical fibre are used to realise distributed fibre optic sensing(DFOS)systems for measuring various parameters.Rayleigh,Brillouin,and Raman backscattering provide different sensitivit...Backscattered lightwaves from an optical fibre are used to realise distributed fibre optic sensing(DFOS)systems for measuring various parameters.Rayleigh,Brillouin,and Raman backscattering provide different sensitivities to different measurands and have garnered the attention of researchers.A system combining the three principles above can effectively separate the measured strain and temperature completely as well as provide measurements of both dynamic and static parameters.However,the combined system is extremely complicated if the three systems are independent of each other.Hence,we propose a single-end hybrid DFOS system that uses two successive pulses to realise the Brillouin amplification of Rayleigh backscattering lightwaves for combining Rayleigh and Brillouin systems.A 3-bit pulse-coding method is employed to demodulate the Raman scattering of the two pulses to integrate Raman optical time-domain reflectometry into the hybrid system.Using this hybrid scheme,a simultaneous measurement of multiple parameters is realised,and a favourable measurement accuracy is achieved.展开更多
In extracting vertical profiles of aerosol backscattering coefficient from lidar signals, the effects of atmo- spheric temperature are usually ignored, In this study, these effects are analyzed using a rotational Rama...In extracting vertical profiles of aerosol backscattering coefficient from lidar signals, the effects of atmo- spheric temperature are usually ignored, In this study, these effects are analyzed using a rotational Raman-Mie lidar system, which is capable of simultaneously measuring atmospheric temperature and vertical profiles of aerosols, A method is presented to correct the aerosol backscattering coefficient using atmospheric temperature profiles, obtained from Raman scattering signals. The differences in the extracted aerosol backscattering coefficient with and without considering temperature effects are fur- ther discussed. The backscattering coefficients for scattering off clouds are shown to be more sensitive to temperature than that of aerosols and atmosphere molecules; the aerosol backscattering coefficient is more sensitive to temperature in summer due to higher atmospheric temperatures,展开更多
基金support from grant ANR-11-IDEX-0004-02 Plas@Parsupport from the project ELI:Extreme Light Infrastructure (CZ.02.1.01/0.0/ 0.0/15-008/0000162) from European Regional Development
文摘The co-existence of the Raman and Brillouin backscattering instability is an important issue for inertial confinement fusion. The present paper presents extensive one-dimensional(1D) particle-in-cell(PIC) simulations for a wide range of parameters extending and complementing previous findings. PIC simulations show that the scenario of reflectivity evolution and saturation is very sensitive to the temperatures, intensities, size of plasma and boundary conditions employed. The Langmuir decay instability is observed for rather small k_(epw)λ_D but has no influence on the saturation of Brillouin backscattering, although there is a clear correlation of Langmuir decay instability modes and ion-fractional decay for certain parameter ranges. Raman backscattering appears at any intensity and temperature but is only a transient phenomenon. In several configurations forward as well as backward Raman scattering is observed. For the intensities considered, I λ_o^2 above 10^(15) W μm^2/cm^2, Raman is always of bursty nature. A particular setup allows the simulation of multi-speckle aspects in which case it is found that Raman is self-limiting due to strong modifications of the distribution function. Kinetic effects are of prime importance for Raman backscattering at high temperatures. No unique scenario for the saturation of Raman scattering or Raman–Brillouin competition does exist. The main effect in the considered parameter range is pump depletion because of large Brillouin backscattering. However, in the low k_(epw)λ_D regime the presence of ion-acoustic waves due to the Langmuir decay instability from the Raman created electron plasma waves can seed the ion-fractional decay and affect the Brillouin saturation.
基金funding from the National Natural Science Foundation of China(NSFC)under grant numbers 61735015,62275151the Major Key Project of PCL.
文摘Backscattered lightwaves from an optical fibre are used to realise distributed fibre optic sensing(DFOS)systems for measuring various parameters.Rayleigh,Brillouin,and Raman backscattering provide different sensitivities to different measurands and have garnered the attention of researchers.A system combining the three principles above can effectively separate the measured strain and temperature completely as well as provide measurements of both dynamic and static parameters.However,the combined system is extremely complicated if the three systems are independent of each other.Hence,we propose a single-end hybrid DFOS system that uses two successive pulses to realise the Brillouin amplification of Rayleigh backscattering lightwaves for combining Rayleigh and Brillouin systems.A 3-bit pulse-coding method is employed to demodulate the Raman scattering of the two pulses to integrate Raman optical time-domain reflectometry into the hybrid system.Using this hybrid scheme,a simultaneous measurement of multiple parameters is realised,and a favourable measurement accuracy is achieved.
文摘In extracting vertical profiles of aerosol backscattering coefficient from lidar signals, the effects of atmo- spheric temperature are usually ignored, In this study, these effects are analyzed using a rotational Raman-Mie lidar system, which is capable of simultaneously measuring atmospheric temperature and vertical profiles of aerosols, A method is presented to correct the aerosol backscattering coefficient using atmospheric temperature profiles, obtained from Raman scattering signals. The differences in the extracted aerosol backscattering coefficient with and without considering temperature effects are fur- ther discussed. The backscattering coefficients for scattering off clouds are shown to be more sensitive to temperature than that of aerosols and atmosphere molecules; the aerosol backscattering coefficient is more sensitive to temperature in summer due to higher atmospheric temperatures,
