Sodium guide star technologies for Adaptive Optics (AO) have been around for over 20 years. During this time, the technologies for the lasers used to excite the mesospheric sodium have been in constant development, with the goals being not only to excite as much sodium as possible, but to do so efficiently, while producing a round guide star, and while offering a reliable facility. The first lasers in use were dye lasers with a liquid gain medium, while these lasers were able to produce sodium guide stars, the liquid dye used was toxic and flammable. The second generation of guide star lasers used sum-frequency-mixed solid-state lasers. These lasers provided excellent return but were notoriously difficult to calibrate and maintain, requiring a full-time laser engineer on staff. The current third generation of sodium guide star lasers use Raman fiber amplification to generate a laser that is very efficient at exciting sodium with a good spot profile and offer a high degree of reliability. The Gemini South observatory for the last few years has been in the process of obtaining one of these third-generation lasers, a Toptica Sodium Star 20/2 while maintaining its second-generation Lockheed Martin Coherent Technologies (LMCT) 50W CW Mode-locked laser. In October of 2017 successful on-sky commissioning of the Toptica laser was executed while the LMCT laser was still active and in operations. During the course of the commissioning run both lasers were used on sky in close in time in possible. We present a comparative study of the performance of each laser.
Adaptive Optics (AO) systems aim at detecting and correcting for optical distortions induced by atmospheric turbulences. The Gemini Multi Conjugated AO System GeMS is operational and regularly used for science observations since 2013 delivering close to diffraction limit resolution over a large field of view. GeMS entered this year into a new era. The laser system has been upgraded from the old 50W Lockheed Martin Coherent Technologies (LMCT) pulsed laser to the Toptica 20/2W CW SodiumStar laser. The laser has been successfully commissioned and is now used regularly in operation. In this paper we first review the performance obtained with the instrument. I will go then into the details of the commissioning of the Toptica laser and show the improvements obtained in term of acquisition, stability, reliability and performance.