Column-density meter: a high precision technique for measuring line-of-sight vapor densities

A technique suitable for making automated high precision (1%) measurements of column densities Nl in vapor cells and ovens will be presented. The method employs a single-pass low finesse interferometer (e.g., a Mach-Zehnder), a broadband light source, and a 1024-element diode array in the image plane of a stigmatic spectrograph to measure photometrically the frequency-dependent intensity profiles of distorted interference fringes produced by the anomalous dispersion near an absorption line. Experimental measurements of Ba, Ca, and Li column densities show that Nl can be determined with high precision by numerically fitting a small segment (5–20 nm) of the spectrum to a simple analytic expression describing the intensity.