Measurements of Anomalous Dispersion of HF in Absorption

The quantitative measurement of the anomalous dispersion of the P1(6), P1(7), and P1(8) vibration-rotation transitions of hydrogen-fluoride (HF) in absorption are reported. The measurements were performed with a small, line-selectable HF laser equipped with a piezoelectrically frequency-scanned cavity that illuminated a Mach-Zehnder interferometer, one arm of which contained the HF absorption cell. The fringes produced by the interferometer and their dispersion-induced shift were observed directly with the help of a rotating mirror and an ir detector. This interferometer technique has an ultimate noise-limited sensitivity of 0.02 of a fringe spacing at 2.7 micron. Measurements also are given for the absorption coefficient at line center for the same three P1 lines of HF. Both dispersion and absorption measurements are for a pressure range of 0.05 to 10 Torr of pure HF at room temperature, so the absorption lines were Doppler broadened. The measured values for the absorption coefficient and the slope of the dispersion curve at line center and for the maximum excursion of the anomalous refractive index are in excellent agreement with calculated values for these quantities. (Author)