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 $P14\mathrm{}$ and $P30\mathrm{}$ lines of two oppositely directed cw C${\mathrm{O}}_2$ lasers at 9.4 μm with the $R{(1, 1)}_{0\to {\nu }_3}$ and $R{(2, 1)}_{{\nu }_3\to 2{\nu }_3}$ lines of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ ${\mathrm{H}}_3$F are used to measure the pressure-broadening coefficient ($\Delta {\nu }_p=41.3\mathrm{}\pm 1.0$ MHz/Torr) and pressure shift ($\Delta {\nu }_s=2.1\mathrm{}\pm 0.1$ MHz/Torr) of the $0\to 2{\nu }_3$ transition.