Optical designs with wide field-of-view adaptive optics for IMAKA of CFHT

As a ground-layer adaptive optics (GLAO) system can correct the wavefront errors caused by turbulence close to the Canada-France-Hawaii telescope (CFHT), an intensive study is in progress to determine the feasibility and the pertinence of equipping the CFHT of such a GLAO system. More specifically, the study concerns the implementation of GLAO capabilities using a deformable mirror inserted into the optical path of an optical relay. The studied system called IMAKA would be used both for the dynamic correction of the wavefront errors caused by air turbulence and the increases of the telescope effective field of view. The objective pursued by IMAKA is to achieve a PSF with Full Width at Half Maximum of less than 0.15" over a 1-degree field of view for extended wavebands within the spectral waveband of 470 nm - 900 nm. This paper presents the main results of a study conducted by INO about the optical design challenges of the IMAKA system. INO has proposed 4 different approaches for the realization of the system and made preliminary optical designs for each of them. The science camera and deformable mirror in the proposed designs are located below the Cassegrain environment for three of the proposed configurations and between the primary mirror and the top ring for the fourth design. In all the proposed configurations, the effective focal length of the telescope with the added correction relay is about 20.63 m for a working focal ratio of about 5.74. The design configurations included in this paper have achieved nearly diffraction limited performances with a deformable mirror having a diameter inferior to 0.5 m and flat or mild curvature nominal shape. Based on our preliminary optical design and performance analysis with the 4 optical design approaches, it seems possible to achieve most of the IMAKA requirements.