Identification of Absorption Lines by Modulated Lower-Level Population: Spectrum ofNa2

Molecular absorption lines from a common lower level are intensity modulated by chopped-laser saturation of another line from that level. Populations of some other levels are also modulated by subsequent fluorescence. Both types of modulated lines are free of Doppler broadening. Also, collisional depopulation modulates absorption from rotational levels near the laser-depleted level. In ${\mathrm{Na}}_2$, we have identified 113 lines. Analysis of the $A$ state by Kusch and Hessel is confirmed and extended.