Saturation in laser-induced fluorescence: effect on alignment parameters

Abstract

A method for extracting the alignment parameters of a molecular angular momentum distribution using laser-induced fluorescence is presented. The treatment is applicable to the common case of cylindrically symmetric orientation distributions in the high- J limit. Four different combinations of rotational branches in the LIF absorption emission process are examined for experimental arrangements without external fields as well as with an applied strong magnetic field. Computer algebra programs are used to generate simple analytical expressions which account for the influence of saturation on determining alignment parameters. In this analysis saturation effects can be calculated without any prior knowledge of the orientational distribution. It is found that an exact treatment is necessary even at a relatively low saturation and in most cases it can be carried out with only a limited knowledge of the saturation conditions.