The observation of diffusion as an effective vibrational relaxation rate in CO2

A differential absorption signal of 10.6-μ radiation by a CO
2
cell in the alternating presence and absence of a partially saturating beam on a different transition is observed as a function of increasing pressure of helium. The linear increase with pressure at low pressures is explained as a result of diffusion acting as a strong effective vibration relaxation rate. The behavior as a function over the entire observed pressure range is well described by combining simple collision and diffusion effects.