HARMONI at ELT: a telescope simulator for laser tomographic AO

Abstract

HARMONI is the first light visible and near-IR integral field spectrograph for the ELT. It covers a large spectral range from 450nm to 2450nm with resolving powers from 3500 to 18000 and spatial sampling from 60mas to 4mas. It can operate in two Adaptive Optics modes -SCAO (including a High Contrast capability) and LTAO -or with NOAO. The project is preparing for Final Design Reviews. The AO wavefront sensor modules are assembled and tested in Marseille, requiring a large telescope simulator for realistic projection of various guide objects into the system. This is particularly challenging for the six laser guide stars, whose partially overlapping beams converge to a focus several meters behind the instrument entrance focus. To avoid building a well-corrected, meter-sized, optical system for this task, a single large lens is employed, associated with source modules individually equipped with spatial light modulators (SLM) capable both of simulating the atmosphere and the telescope's deformable mirror (M4) and of compensating the aberrations inherent to the simple simulator optics. In this paper, we present preliminary optical designs for the telescope simulator and the source units. We also describe prototype work, associated with theoretical analysis, to demonstrate the SLM's capabilities for generating sufficiently large aberrations.