Pressure Shift and Broadening of Methane Line at 3.39<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>μ</mml:mi></mml:math>Studied by Laser-Saturated Molecular Absorption

Abstract

We study broadening and the anomalously small shift of a $3.39\ensuremath{-}\ensuremath{\mu}$ rotation-vibration line of methane at millitorr pressures. Saturation by the laser intracavity field allows investigation of the very sharp natural linewidth, without Doppler broadening. Two lasers were independently locked to this transition with an offset of less than \ifmmode\pm\else\textpm\fi{}1 kHz, a reproducibility of \ifmmode\pm\else\textpm\fi{}1 \ifmmode\times\else\texttimes\fi{} ${10}^{11}$.