Investigations of long pulse sodium laser guide stars

Long pulse length sodium laser guide stars (LGS) are useful because they allow for Rayleigh blanking and fratricide avoidance in multiple LGS systems. Bloch equation simulations of sodium-light interactions in Mathematica show that certain spectral formats and pulse lengths, on the order of 30 microseconds, with high duty cycles (20-50%) should be able to achieve photon returns within 10% of what is seen from continuous wave (CW) excitation. In this work, we investigate the time dependent characteristics of sodium fluorescence, and find the optimal format for the new LGS that will be part of the upgraded AO system on the Shane 3 Meter telescope at Mt. Hamilton. Results of this analysis are discussed along with their general applicability to other LGS systems. The potential benefits of uplink correction are also considered.

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