Measurements of the anomalous dispersion of HF in absorption

We report quantitative measurements of the anomalous refractive index of the
P_{1}(6),P_{1}(7)
, and
P_{1}(8)
vibration-rotational transitions of hydrogen fluoride in absorption. The experimental technique uses the displacement of spatial fringes produced by a Mach-Zehnder interferometer containing the absorption cell. A frequency scanned, CW HF probe laser served as the light source and the spectrally selective element. In addition, we measured the absorption coefficient of the three transitions. The experimental results are in good agreement with calculated values derived from the transition-matrix theory of HF.