PASS-2: photometry of the polychromatic laser guide star

PASS-2 is an experiment designed to perform photometry of the polychromatic laser guide star. The tilt of an atmospherically distorted wave front coming from an astronomical object cannot be determined with a monochromatic laser guide star. If it is possible to produce a laser guide star that emits light at different wavelengths, however, the tilt can be determined from the measurable differences between the tilts at the different wavelengths. This is the concept of the polychromatic laser guide star. The PASS-2 experiment is a step towards an implementation of an adaptive optics system that uses a polychromatic laser guide star for the wave front tilt measurement. The goal of the experiment is to validate the feasibility of a polychromatic laser guide star adaptive optics system and to determine the laser parameters that produce the optimal return flux from the polychromatic laser guide star. To this end, the return flux from the polychromatic laser guide star at 330 and 589.6 nm will be measured as a function of laser parameters, atmospheric conditions, and the density of the mesospheric sodium layer.