HARMONI at ELT: designing a laser guide star wavefront sensors for the ELT

• Main Authors: Costille, Anne, Bonnefoi, Anne, Renault, Edgard, Ceria, William, Dohlen, Kjetil, Neichel, Benoit, Hubert, Zoltan, Correia, Jean-Jacques, Moulin, Thibaut, Mendoza, Saul Menendez, Fusco, Thierry, Vola, Pascal, Pedreros, Felipe, Jouve, Pierre, Kacem, El, Hadi, Fraser, Schnetler, Hermine, Melotte, Dave, Thatte, Niranjan
• Format: Journal Article
• Language: English
• Published: 18-07-2022
• Subjects: Physics - Instrumentation and Methods for Astrophysics
• DOI: 10.48550/arxiv.2207.08451

SPIE Astronomical Telescopes + Instrumentation 2022, Jul 2022,
Montr{\'e}al, Canada HARMONI is the first light visible and near-IR integral field spectrograph
for the ELT covering 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 and LTAO-or with no AO. The project
is preparing for Final Design Reviews. The laser Tomographic AO (LTAO) system
provides AO correction with very high sky-coverage thanks to two systems: the
Laser Guide Star Sensors (LGSS) and the Natural Guide Star Sensors (NGSS). LGSS
is dedicated to the analysis of the wavefront coming from 6 laser guide stars
created by the ELT. It is made of 6 independent wavefront sensor (WFS) modules
mounted on a rotator of 600mm diameter to stabilise the pupil onto the
microlens array in front of the detector. The optical design accepts elongated
spots of up to 16 arcsec with no truncation using a CMOS detector from SONY. We
will present the final optical and mechanical design of the LGSS based on
freeform lenses to minimize the numbers of optical components and to
accommodate for the diversity of sodium layer configurations. We will focus on
rotator design, illustrating how we will move 1 tons with 90" accuracy in
restrictive environment. Finally, we will present the strategy to verify the
system in HARMONI context. The main challenge for the verification being how to
test an AO system without access to the deformable mirror, part of the ELT.