Precision measurements of sodium-sodium and sodium-noble gas molecular absorption

Abstract

Experimental apparatus and measurement technique are described for precision\nabsorption measurements in sodium - noble gas mixtures. The absolute absorption\ncoefficient is measured in the wavelength range from 425 nm to 760 nm with 2%\nuncertainty and spectral resolution of 0.02 nm. The precision is achieved by\nusing a specially designed absorption cell with an accurately defined\nabsorption path length, low noise CCD detector and double-beam absorption\nmeasurement scheme. The experimental set-up and the cell design details are\ngiven. Measurements of sodium atomic number density with 5% uncertainty\ncomplement absorption coefficient measurements and allow derivation of the\nreduced absorption coefficients for certain spectral features. The sodium\natomic number density is measured using the anomalous dispersion method. The\naccuracy of this method is improved by employing a least-squares fit to the\ninterference image recorded with CCD detector and the details of this technique\nare given. The measurements are aimed at stringent testing of theoretical\ncalculations and improving the values of molecular parameters used in\ncalculations.\n