Near-Resonant Rayleigh Scattering Method for Measurements of Alkali Atomic Density in Combustion Gas Plasmas

This paper reports the development of a non-intrusive, space-resolved method for density measurements of alkali atoms in combustion gas plasmas. A sodium density of over 10¹⁴cm^-3in an air-acetylene flame was measured using a near-resonant Rayleigh scattering (NRRS) method, in which the wavelength of the incident laser was detuned from the resonance line of the sodium atoms in order to avoid reabsorption of the scattered signal light. The results agree fairly well with those obtained by the spectral absorption method and the Na reference cell method. The results show that the NRRS method described here can also be used to measure atomic densities of the order of 10¹⁶cm^-3typical values in an open-cycle MHD power-generation plasma.