Abstract
Spontaneous RayleighBrillouin (RB) scattering experiments have been performed in air for pressures in the range 0.25–3 bar and temperatures in the range 273–333 K. The functional behaviour of the RBspectral profile as a function of experimental parameters, such as the incident wavelength, scattering angle, pressure and temperature is analysed, as well as the dependence on thermodynamic properties of the gas, as the shear viscosity, the thermal conductivity, the internal heat capacity and the bulk viscosity. Measurements are performed in a scattering geometry detecting at a scattering angle (Formula presented.) and an incident wavelength of (Formula presented.), at which the Brillouin features become more pronounced than in a right angles geometry and for ultraviolet light. For pressure conditions of 1–3 bar the RBspectra, measured at high signaltonoise ratio, are compared to TentiS6 model calculations and values for the bulk viscosity of air are extracted. Values of (Formula presented.) are found to exhibit a linear dependence on temperature over the measurement interval in the range (Formula presented.). A temperature dependent value is deduced from a collection of experiments to yield: (Formula presented.). These results are implemented in model calculations that were verified for the low pressure conditions (p<1 bar) relevant for the Earth's atmosphere. As a result we demonstrate that the RBscattering spectral profiles for air under subatmospheric conditions can be generated via the TentiS6 model, for given gasphase and detection conditions (p, T, (Formula presented.), and θ), and for values for the gas transport coefficients. Spectral profiles for coherent RBscattering in air are also computed, based on the TentiS6 formalism, and the predictions are compared with profiles of spontaneous RBscattering. Finally data on RBscattering in air, obtained under a variety of pressure, temperature, wavelength and scattering angles, are analysed in terms of universal scaling, involving the dimensionless uniformity parameter y and the dimensionless frequency x. Such scaling behaviour is shown to be well behaved for a wide parameter space and implies that RBscattering spectra can be generated for a wide range of atmospheric applications of RBscattering. The verification of this dimensionless scaling also shows that air can be treated as an ideal gas in the atmospheric regime, where (Formula presented.).
Original language  English 

Article number  e1804635 
Pages (fromto)  116 
Number of pages  16 
Journal  Molecular Physics 
Volume  119 
Issue number  12 
Early online date  20 Aug 2020 
DOIs  
Publication status  Published  Jan 2021 
Keywords
 earth's atmosphere
 gas transport coefficients
 ideal gases
 light scattering
 Spontaneous RayleighBrillouin scattering
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RayleighBrillouin light scattering spectroscopy of air; experiment, predictive model and dimensionless scaling
Wang, Y. (Contributor), Gu, Z. (Contributor), Liang, K. (Contributor) & Ubachs, W. (Contributor), Unknown Publisher, 1 Jan 2020
DOI: 10.6084/m9.figshare.12854544.v2, https://tandf.figshare.com/articles/dataset/RayleighBrillouin_light_scattering_spectroscopy_of_air_experiment_predictive_model_and_dimensionless_scaling/12854544/2
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RayleighBrillouin light scattering spectroscopy of air; experiment, predictive model and dimensionless scaling
Wang, Y. (Contributor), Gu, Z. (Contributor), Liang, K. (Contributor) & Ubachs, W. (Contributor), Unknown Publisher, 1 Jan 2020
DOI: 10.6084/m9.figshare.12854544.v1, https://tandf.figshare.com/articles/dataset/RayleighBrillouin_light_scattering_spectroscopy_of_air_experiment_predictive_model_and_dimensionless_scaling/12854544/1
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RayleighBrillouin light scattering spectroscopy of air; experiment, predictive model and dimensionless scaling
Wang, Y. (Contributor), Gu, Z. (Contributor), Liang, K. (Contributor) & Ubachs, W. (Contributor), Unknown Publisher, 1 Jan 2020
DOI: 10.6084/m9.figshare.12854544, https://tandf.figshare.com/articles/dataset/RayleighBrillouin_light_scattering_spectroscopy_of_air_experiment_predictive_model_and_dimensionless_scaling/12854544
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