Contrast of an inverted Lamb dip of a laser with an internal absorption cell

The rate equations approximation is used in a calculation of the contrast of an inverted Lamb dip of a laser with an internal absorption cell. An approximate solution is obtained for the dependence of the contrast on the pressure in the absorption cell. Theoretical results are compared with the experimental data obtained with the aid of an He-Ne laser at a wavelength of 3.39 μ. It is shown that some information on the quantitative composition of a mixture of gases can be obtained by spectroscopy inside a Doppler line.