A systematic study of Rayleigh-Brillouin scattering in air, N2, and O2 gases

Abstract

Spontaneous Rayleigh-Brillouin scattering experiments in air, N 2 and O 2 have been performed for a wide range of temperatures and pressures at a wavelength of 403 nm and at a 90 degrees scattering angle. Measurements of the Rayleigh-Brillouin spectral scattering profile were conducted at high signal-to-noise ratio for all three species, yielding high-quality spectra unambiguously showing the small differences between scattering in air, and its constituents N 2 and O 2 . Comparison of the experimental spectra with calculations using the Tenti S6 model, developed in 1970s based on linearized kinetic equations for molecular gases, demonstrates that this model is valid to high accuracy for N 2 and O 2 , as well as for air. After previous measurements performed at 366 nm, the Tenti S6 model is here verified for a second wavelength of 403 nm, and for the pressuretemperature parameter space covered in the present study (250 -340 K and 0.6 -3 bar). In the application of the Tenti S6 model, based on the transport coefficients of the gases, such as thermal conductivity κ, internal specific heat capacity c int and shear viscosity η as well as their temperature dependencies taken as inputs, values for the more elusive bulk viscosity η b for the gases are derived by optimizing the model to the measurements. It is verified that the bulk viscosity parameters obtained from previous experiments at 366 nm, are valid for wavelengths of 403 nm. Also for air, which is treated as a single-component gas with effective gas transport coefficients, the Tenti S6 treatment is validated for 403 nm as for the previously used wavelength of 366 nm, yielding an accurate model description of the scattering profiles for a range of temperatures and pressures, including those of relevance for atmospheric studies. It is concluded that the Tenti S6 model, further verified in the present study, is applicable to LIDAR applications for exploring the wind velocity and the temperature profile distributions of the Earth's atmosphere. Based on the present findings at 90• scattering and the determination of η b values predictions can be made on the spectral profiles for a typical LIDAR backscatter geometry. These Tenti S6 predictions for Rayleigh-Brillouin scattering deviate by some 7% from purely Gaussian profiles at realistic sub-atmospheric pressures occurring at 3-5 km altitude in the Earth's atmosphere.

Rayleigh–Brillouin light scattering spectroscopy of nitrous oxide (N2O)

“…2) does not provide a symmetry point as is the case for CO 2 [31]. While a number of recent studies were performed to model RB-scattering in diatomic molecules [17,18,7,12] the quest is now to investigate RB-scattering in polyatomic molecules of different symmetry and sizes. N 2 O is a convenient target in view of its large scattering cross section [26].…”

“…Later this model was revived after investigations were performed involving coherent RB scattering for which RBS codes were developed by Pan et al [29,14]. Those codes were applied to describe both coherent RB scattering [30] and spontaneous RB scattering in CO 2 [31] and in nitrogen, oxygen and air [12]. In those studies it was established that the S6-version of the Tenti model yields a better agreement with experiment than an alternative S7version.…”

“…In the decade after the invention of the laser numerous studies have been performed measuring the spectral profile of Rayleigh-Brillouin scattering with the goal to derive collisional properties of gaseous media [5,6,7,8]. More recently the field of RB-scattering has been revived with the goal to monitor gas flow and the conditions of the Earth's atmosphere [9,10,11,12]. Independently, in addition to conventional spontaneous RB scattering, methods of coherent RB scattering have been developed for the investigation of collisional phenomena in gases [13,14,15,16].…”

Rayleigh-Brillouin scattering in SF6 in the kinetic regime

“…Line shape models that take the transport coefficients of macroscopic gas dynamics as input are attractive because they can be used to measure these transport coefficients at very large frequencies by comparing measured scattered light spectra to models. In this manner we have recently studied Spontaneous Rayleigh-Brillouin scattering-profiles of N 2 [19] and CO 2 [18], while it was also used to describe RB-scattering in air, where air was treated as a mono-molecular species [20,21]. In the same fashion, the bulk viscosity of several polar and non-polar polyatomic gases was studied using Coherent Rayleigh-Brillouin scattering [22].…”

Spontaneous Rayleigh-Brillouin scattering spectral analysis based on the Wiener filter

“…Many gas properties can be obtained by the analysis of SRBS signal, such as the temperature, pressure and bulk viscosity parameters. 1,2 After the invention of laser in the 1960s, techniques were developed immediately to measure the characteristic scattering profiles and to resolve the Brillouin doublet peaks shifted from a central elastic Rayleigh peak in the liquid and solid phase 3 and then in the gas phase. 4,5 During the 1970s, detailed studies on SRBS in gas phase media were performed, in particular on molecular hydrogen, 6 on molecular nitrogen, 7 on various polyatomic gases exhibiting internal relaxation, 8 and on scaling laws for the noble gases.…”