Efficiency of 2-photon polychromatic laser guide stars

Polychromatic laser guide stars (PLGS) are created by resonant excitation of the mesospheric sodium by two pulsed lasers at 589 nm and 569 nm respectively. The efficiency of this process is investigated numerically by means of both Bloch equations and rate equations models. The influence of numerous laser parameters is studied. For 2×25 W laser average power the return flux is below 105 photons/s/m2