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Optical pumping in a thin Cs vapor cell (end-wall gap 0.5–10 mm) transfers only atoms with small velocity components to a certain energy state. The non-Maxwellian velocity distribution is detected as a hyperfine-resolved spectrum by a double resonance technique using diode lasers. The observed spectral profiles are quantitatively reproduced by the rate-equation analysis in which the velocity-dependent surface relaxation process is taken into account.

We propose a novel method of stabilizing laser oscillation frequency that uses a sub-Doppler spectrum of atoms in a thin vapor cell. An extended-cavity diode laser is frequency-locked to a hyperfine component of the Cs-D(2) line. In the Allan-variance measurements on the beat note between two lasers thus stabilized, a frequency stability of 6.6x10(-11) is achieved at an averaging time of 5.8 s. The frequency can be controlled even when the laser beam intensity is as small as 70 nW/cm(2).

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The optimal buffer-gas condition for achieving low noise in room temperature optical-pumped magnetometers (OPMs) was determined. To find this optimal condition, various buffer gases (helium, neon, argon, and nitrogen) filled in cesium cells at pressures of 1, 10, 50, 300, or 1000 Torr were tested. Magnetic-resonance signal was detected by sweeping rf frequency, and maximum intensity (I max) and line width (Δf) in the magnetic-resonance spectra were measured. As an appropriate figure of merit for OPMs, the “α value” (i.e., I max/Δf) is defined. It was found that the α value of the cells decreased as gas pressure increased. The α value obtained from the cell filled with neon gas (at 1 Torr) at optimal rf field of 50 nT was the largest. It was inferred from these results that the spin-destruction collision between cesium atoms and the buffer gas has a significant influence on the α value.