Density gradient rubidium dispersive absorption filter for low wavenumber Raman and Thomson scattering
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A new approach for low wavenumber Raman and forward Thomson scattering, based on a combination of rubidium dispersive absorption filter and narrow line-width Ti: Sapphire laser, has been developed. This filter not only spatially disperses the low wavenumber Raman or Thomson scattering but strongly attenuates particle and Rayleigh scattering. The density gradient rubidium filter has large dispersion power and high optical throughput. A variable high rubidium density gradient perpendicular to the light propagation direction is created by the process of rubidium vapor diffusion through helium buffer gas. Both the dispersion and transmission characteristics near the rubidium D2 line (around 780.03nm) are experimentally studied for different vapor gradient conditions. A theoretical model based on the change of index of refraction and the absorption spectral profile predicts the spatial deviation and attenuation of Rayleigh, Raman or Thomson scattering radiation for various vapor density gradients. The model is verified by experimental data. A scheme to optimally operate the filter has been proposed. The filter also achieves high optical density without the problem of window condensation. As a demonstration, the rotational Raman spectrum of CO2 has been obtained with the new filter.
author list (cited authors)
Tang, Z., Zaidi, S. H., & Miles, R. B.
Tang, Z., Zaidi, S., & Miles, R.