We report on our systematic investigation of strong Doppler-free two-photon absorption in the middle infrared. The absorption frequencies for two counterpropagating waves of identical frequencies are predicted. Five of these transitions were observed with sub-Doppler resolution with a sideband CO2 laser and were measured with 10-kHz accuracy. Knowledge of these strong two-photon absorptions frequencies will allow the improvement of secondary frequency standards in the infrared.
© 1998 Optical Society of America
F. Herlemont, M. Khelkhal, J. Legrand, and G. Pierre, "Doppler-free two-photon spectrum of SF6 for metrological purposes," Opt. Lett. 23, 957-959 (1998)