Anomalous Saturated-Absorption Pressure Shifts in CO2

Abstract

Pressure shifts of the standing-wave saturated resonance have been measured in the 9-and 10-μm $P$ and $R$ lasing transitions of C${\mathrm{O}}_2$ with a heterodyne spectroscopic technique. At low pressures (≤100 m Torr) the measured shifts for four different isotopes were all blue, instead of red as predicted by semiclassical theory. Measurements at higher (> 1 Torr) pressures revealed red shifts. Perturber-gas data showed blue shifts for heavier perturber atoms or molecules, red shifts for He and ${\mathrm{H}}_2$.