Prototyping activities of laser/natural guide star wavefront sensors for ULTIMATE-Subaru GLAO

Abstract

ULTIMATE-Subaru is the next-generation facility instrument project at the Subaru Telescope, Hawaii. One of its key development components is Ground Layer Adaptive Optics (GLAO), which improves image performance at the K-band by a factor of ∼ 2 compared to seeing conditions over a wide field of view of 20 arcmin in diameter. In the GLAO system, the Wavefront Adaptor Flange including four laser guide star wavefront sensors (LWFS) and four natural guide star wavefront sensors (NWFS) is mounted at the Cassegrain focus of the Subaru Telescope to measure the wavefront by ground layer turbulence. The LWFS and NWFS can move to select stars in 2-10 arcmin and 7-10 arcmin from the center of the field of view, respectively, while accommodating effects from the field curvature and non-telecentricity of the telescope. Prototyping activities of the wavefront sensor system are ongoing at the Australian National University (ANU). Single LWFS and single NWFS are assembled and optically aligned in the laboratory to test optical and mechanical performances. To make the simulated source representative of the telescope’s off-axis beams both in terms of the incoming angle and the position of the focus, we also manufacture a prototype of the star simulator, which introduces a set of artificial sources to calibrate encoders of the wavefront sensor mechanisms. In this presentation, we provide an overview of the GLAO wavefront sensor system and the prototyping activities carried out in the ANU laboratory with their purposes and procedures.