= Sodium saturation spectroscopy experiment of 1971
<Theodor W. Hänsch>, <I. S. Shahin> and <Arthur Leonard Schawlow> reported pulsed <dye laser> <saturation spectroscopy> of <sodium> D lines in 1971. They resolved <hyperfine structure>; delaying the probe revealed persistent changes in ground-level distributions of <velocities> from <optical pumping>. Added <argon> allowed observation of collisional recovery. These measurements probe population memory as well as line positions.<High-Resolution Saturation Spectroscopy of the Sodium D Lines with a Pulsed Tunable Dye Laser by Theodor W. Hänsch and others>[Hänsch, Shahin and Schawlow, 1971, abstract; published September 13]{ref}
The <two-level saturation population model> explains depletion in a closed transition; the delayed multilevel <optical pumping> signal needs additional populations and time dependence. A measured <Doppler-free saturation spectroscopy> feature can still contain <natural linewidth>, <power broadening>, <pressure broadening>, finite interaction time, imperfect alignment and laser spectral width. The word “Doppler-free” removes a particular thermal broadening mechanism, not every limit on resolution.
<Arthur Leonard Schawlow>'s 1981 recognition concerned <laser spectroscopy>.<Professional profile of Arthur Leonard Schawlow>[Stanford Physics, career history: 1981 Nobel Prize]{ref} <Theodor W. Hänsch> received a distinct award in 2005 for precision <laser spectroscopy>.<Physik-Nobelpreis 2005 an Theodor W. Hänsch by Max Planck Society>[Max Planck Society, October 4, 2005, opening and award explanation]{ref}
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