Observation of Doppler-Free Two-Photon Absorption in theν3Bands of CH3F

Abstract

We report the first observation of Doppler-free two-photon absorption in a molecule using two fixed-frequency infrared optical fields in combination with molecular Stark tuning. The coincidences of the $P14$ and $P30$ lines of two oppositely directed cw C${\mathrm{O}}_{2}$ lasers at 9.4 \ensuremath{\mu}m with the $R{(1, 1)}_{0\ensuremath{\rightarrow}{\ensuremath{\nu}}_{3}}$ and $R{(2, 1)}_{{\ensuremath{\nu}}_{3}\ensuremath{\rightarrow}2{\ensuremath{\nu}}_{3}}$ lines of $^{12}\mathrm{C}$${\mathrm{H}}_{3}$F are used to measure the pressure-broadening coefficient ($\ensuremath{\Delta}{\ensuremath{\nu}}_{p}=41.3\ifmmode\pm\else\textpm\fi{}1.0$ MHz/Torr) and pressure shift ($\ensuremath{\Delta}{\ensuremath{\nu}}_{s}=2.1\ifmmode\pm\else\textpm\fi{}0.1$ MHz/Torr) of the $0\ensuremath{\rightarrow}2{\ensuremath{\nu}}_{3}$ transition.