Absolute absorption on the rubidium D1 line including resonant dipole-dipole interactions

Here we report on measurements of the absolute absorption spectra of dense rubidium vapour on the D-1 line in the weak-probe regime for temperatures up to 170 degrees C and number densities up to 3 x 10(14) cm(-3). In such vapours, modifications to the homogeneous linewidth of optical transitions arise due to dipole-dipole interactions between identical atoms, in superpositions of the ground and excited states. Absolute absorption spectra were recorded with a deviation of 0.1% between experiment and a theory incorporating resonant dipole-dipole interactions. The manifestation of dipole-dipole interactions is a self-broadening contribution to the homogeneous linewidth, which grows linearly with number density of atoms. Analysis of the absolute absorption spectra allows us to ascertain the value of the self-broadening coefficient for the rubidium D-1 line: beta/2 pi = (0.69 +/- 0.04) x 10(-7) Hz cm(3), in excellent agreement with the theoretical prediction.