Absolute measurement of very low sodium-vapor densities using laser resonance fluorescence*

By use of a cw dye laser, the resonance-fluorescence method is used to make absolute density measurements of sodium vapor from 102 atoms/cm3 at −28 °C to 1011 atoms/cm3 at 144 °C. The results are compared with other measurements at higher temperature by a thermodynamic analysis. A new vapor-pressure curve is derived, which is slightly different from previous curves based on the higher-temperature measurements. The application of laser resonance fluorescence to other species is also discussed. In particular, a scheme for detecting sodium-quark atoms, if they exist, with a sensitivity of nq/nB ~ 10−15, is proposed.