  Absorption imaging of ultracold atoms is the foundation for quantitative
extraction of information from experiments with ultracold atoms. Due to the
limited exposure time available in these systems, the signal-to-noise ratio is
largest for high intensity absorption imaging where the intensity of the
imaging light is on the order of the saturation intensity. In this case, the
absolute value of the intensity of the imaging light enters as an additional
parameter making it more sensitive to systematic errors. Here, we present a
novel and robust technique to determine the imaging intensity in units of the
effective saturation intensity to better than 5%. We do this by measuring the
momentum transferred to the atoms by the imaging light while varying its
intensity. We further utilize the method to quantify the purity of the
polarization of the imaging light and to determine the correct imaging
detuning.
