Keck II laser guide star AO system and performance with the TOPTICA/MPBC laser

Abstract

The Keck II Laser Guide Star (LGS) Adaptive Optics (AO) System was upgraded from a dye laser to a TOPTICA/MPBC Raman-Fibre Amplification (RFA) laser in December 2015. The W. M. Keck Observatory (WMKO) has been operating its AO system with a LGS for science since 2004 using a first generation 15 W dye laser. Using the latest diode pump laser technology, Raman amplification, and a well-tuned second harmonic generator (SHG), this Next Generation Laser (NGL) is able to produce a highly stable 589 nm laser beam with the required power, wavelength and mode quality. The beam's linear polarization and continuous wave format along with optical back pumping are designed to improve the sodium atom coupling efficiency over previously operated sodium-wavelength lasers. The efficiency and operability of the new laser has also been improved by reducing its required input power and cooling, size, and the manpower to operate and maintain it.The new laser has been implemented on the telescope's elevation ring with its electronics installed on a new Nasmyth sub-platform, with the capacity to support up to three laser systems for future upgrades. The laser is projected from behind the telescope's secondary mirror using the recently implemented center launch system (CLS) to reduce LGS spot size. We will present the new laser system and its performance with respect to power, stability, wavelength, spot size, optical repumping, polarization, efficiency, and its return with respect to pointing alignment to the magnetic field. Preliminary LGSAO performance is presented with the system returning to science operations. We will also provide an update on current and future upgrades at the WMKO.

Adaptive optics with an infrared pyramid wavefront sensor at Keck

“…This allows for easy comparison with previous performance tests of the facility AO system. 32,33 5.1 Performance Figure 10 shows the K-band Strehl ratio achieved using the PyWFS, for stars with different H-band magnitudes over a range of nights. The shaded region illustrates that the performance expected from a model of the system (see Sec.…”

The Robo-AO-2 facility for rapid visible/near-infrared AO imaging and the demonstration of hybrid techniques

“…FA error of ~140 nm RMS on 8 to 10-m Sodium LGS AO systems on Maunakea [96] is slightly worse than for the Robo-AO-2 Rayleigh LGS, suggesting that hybrid AO will be more effective on the larger apertures. Extreme AO systems such as GPI (North), SCExAO and the planned Keck Planet Imager and Characterizer [97] will extend their NGS faintness limit when combined with their second generation Sodium LGS [98]. Traditional Sodium laser AO systems can reduce the effects of FA error by implementing hybrid AO with a higher-order NGS WFS instead of just the required NGS tip-tilt-focus sensors.…”

Effect of segmented telescope phasing errors on adaptive optics performance

“…Each telescope is equipped with essentially identical AO systems. 1,2,15,16 There are notable differences between the sodium lasers and associated launch optics, 10,11 and the fact that Keck I has an infrared tip-tilt sensor 12,13 in addition to a visible light one. Three near infrared science instruments operate behind the AO systems.…”