We present results from measurements of the return flux from a polychromatic sodium laser guide star produced in Pierrelatte, France during the PASS-2 experiment. In the experiment, photometry of light at 330, 569, 589, and 589.6 nm emitted by mesospheric sodium under two-color laser excitation (569 and 589 nm) was performed. The variation of oscillator and laser configurations as well as simultaneous measurements of the atmospheric coherence length and the mesospheric sodium density permit a comparison of the results with atomic physics models. Using the results, we can determine the setup that produces the maximum return flux from the polychromatic laser guide star. The knowledge gained will be used to aid the ELP- OA project, which has as its goal the design, testing, and implementation of an adaptive optics system that uses a polychromatic laser guide star for wave front tilt measurements.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.