The two-photon absorption initiated by two coherent beams is considered. It is shown that the resonance fringe variation, which appeared in the Doppler-free two-photon absorption of pulsed laser beams, can also be observed in absorption with a Doppler shift.

Physical Review ASep 1, 19805 citations

Optics Communications

Doppler-free two-photon absorption with a near-resonant intermediate state

D.P. Hodgkinson, J S Briggs

Published Jul 1, 1977• 14 citations

Publisher

DOI: 10.1016/0030-4018(77)90243-7

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{10}^{9}

larger than the case of equal-frequency photons with no loss in resolution.

SATURATION ASPECTS OF TWO-PHOTON SPECTROSCOPY OF

Na_{2}

MOLECULES

We report on the saturation behavior of the

Na_{2}

two-photon transition at 602.17

^nm^{1,2}

This transition has a dominant near-resonant intermediate level; the off-resonance

\\Delta

is of the order of the Doppler width

\\Delta \\nu_{D}

. The dominant contribution to the Doppler-free two-photon line then cornea from two velocity packets of molecules which are Doppler-shifted into resonance. This results in some novel experimentally confirmed aspect, of the two-photon absorption: (i) the ratio of the amplitudes of the Doppler-free and Doppler-broadened two-photon lines is much larger than in the case

\\Delta \\gg \\Delta \\nu_{D}

, and (ii) the Doppler-free line saturates much stronger than the Doppler-broadened line. The resonant velocity packets of molecules are dominantly saturated on the ground-to-intermediate-level transition. The saturation power density is

\\sim 0.5 W/cm^{2}

; this value is consistent with a recent measurement of the Franck-Condon factors

involved^{3}