= Kastler-Brossel optical pumping experiments
{c}
<Alfred Kastler>'s 1966 lecture recalls his 1950 proposal and distinguishes the early $^{23}\mathrm{Na}$ <atomic beam> work from later sealed-vapour experiments. Its Fig. 5 shows subsequent <sodium> <radio wave> resonances, including multiple-<photon> transitions.<Optical methods for studying Hertzian resonances by Alfred Kastler>[1966 lecture, pp. 188–189, 193–194, Fig. 5; inspected authored transcription]{ref}
The 1952 demonstration by <Jean Brossel>, <Alfred Kastler> and <Jacques Winter> used a <sodium> <atomic beam>, lamp <light> with <circular polarization> and <fluorescence> readout. <Jean Brossel> was a central experimental contributor; <Alfred Kastler> received the 1966 <Nobel Prize in Physics> alone.<Jean Brossel by Laboratoire Kastler Brossel>[Direction du laboratoire, 1952 sodium-beam demonstration and Brossel's experimental role]{ref}<The Nobel Prize in Physics 1966 by Nobel Prize Outreach>[Alfred Kastler, prize share 1/1]{ref}
The lecture also describes a $^{199}\mathrm{Hg}$ experiment: a pumping beam with <circular polarization> prepares the vapour, while a perpendicular probe converts transverse <magnetic dipole moment> <Larmor precession> into modulated absorption at a <photodetector>. Interrupting pump and RF together exposes decaying free <Larmor precession>. Its envelope measures transverse relaxation under that model; it is distinct from the <sodium> <atomic beam> <fluorescence> signal.<Optical methods for studying Hertzian resonances by Alfred Kastler>[pp. 196–199, Figs. 9–12: crossed-beam detection and interruption experiment]{ref}
MIT's later <rubidium> experiment pumps natural $^{85}\mathrm{Rb}$/$^{87}\mathrm{Rb}$ with a discharge lamp filtered to D1 ($5S_{1/2}\to5P_{1/2}$, near $795\ \mathrm{nm}$). A <polarizer> and <quarter-wave plate> precede a heated <rubidium>/<neon> cell. <Helmholtz coils> set a weak static <magnetic field>. Separate transverse RF mixing increases absorption, measured by <photodiode> transmission.<Optical Pumping by MIT Department of Physics>[2011 guide, abstract, §V, Fig. 4, §VI.1]{ref}
\Image[/optical-pumping-preparation-and-optical-readout.png]
{title=Vapour-cell preparation and optical transmission readout}
{description=Original functional schematic of the later rubidium-cell apparatus. Geometry is schematic; lamp and interrogation drives are separate.}
Compare resonant and detuned RF with the optical beam fixed, then change the calibrated static <magnetic field>: a true <magnetic sublevel> resonance should move with its <Zeeman splitting>. Lamp drift, stray <magnetic fields>, imperfect <circular polarization>, optical attenuation and RF power broadening can change the observed signal. Consequently, a transmission dip alone does not determine every sublevel population. These are measurement-design considerations, not additional reported historical observations.
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