Precise measurement of density-dependent shift by wavelength modulation reflection spectroscopy

The density dependence of the line shift of the cesium D-2 line is studied with sub-Doppler selective reflection spectroscopy. By use of wavelength mo dulation and sixth-harmonies detection we observed the coefficient of the p ressure-induced shift of the 6S(1/2) (F = 4) --> 6P(3/2) (F ' = 3) hyperfin e transition of the cesium D-2 line Delta delta/rho = -0.9(5) X 10(-8)cm(3) . In the limit rho = 0 a frequency shift about -3MHz remains, which may be attributed to long-range atom-surface interactions. The experimental result s can be used in measurements of the local field-induced frequency shift at high atomic densities with sufficient accuracy.