Implementation of cw- and pulsed-laser beacons for astronomical adaptive optics systems

Artificial beacons generated at the sodium layer have many advantages for adaptive optics (AO) systems in astronomy. The source can be sufficiently bright to achieve high Strehl ratios at infrared wavelengths and because the target object can often be used as the tracking source, photometric field errors can be much reduced compared to off-axis natural beacons. The problem has been to develop a laser that could be tuned to the sodium D 2 line and focused into a compact spot without saturating the layer. Both CW and sum frequency lasers are well suited for this work will be used for the ChAOS AO system described elsewhere in this conference. In this paper we discuss some of the parameters that determine how well CW work, the limitations of pulsed lasers and the development of a 10 watt diode laser pumped sum frequency laser for use in astronomy.