INGOT Wavefront Sensor: from the optical design to a preliminary laboratory test

TL;DR

This paper introduces the Ingot wavefront sensor, a novel optical device designed for ELT Laser Guide Star applications, detailing its optical design, alignment techniques, and preliminary laboratory testing to validate its performance.

Contribution

The paper presents the optical design of the Ingot wavefront sensor, along with innovative alignment procedures and a test-bench for preliminary validation in laboratory conditions.

Findings

Successful design of a reflective roof-shaped prism for LGS wavefront sensing

Development of a new alignment technique based on pupil illumination

Validation of the sensor design through a scaled test-bench

Abstract

The Ingot wavefront sensor is a novel pupil-plane wavefront sensor, specifically designed to cope with the elongation typical of the extended nature of the Laser Guide Star (LGS). In the framework of the ELT, we propose an optical solution suitable for a Laser launch telescope, located outside the telescope pupil. In this paper, we present the current optical design, based on a reflective roof-shaped prism, which, at the level of the focal plane, splits the light from an LGS producing three beams. The three images of the telescope pupils can be then used for the retrieval of the first derivative of the wavefront. The 3D nature of such a device requires new alignment techniques to be determined theoretically and verified in the real world. A possible fully automated procedure, relying solely on the illumination observed at the three pupils, to align the prism to the image of the LGS is discussed. Careful attention needs to be put both on the telecentricity of the system and on the reference systems of the Ingot adjustments in the 3D space. This is crucial in order to disentangle all the possible misalignment effects. In this context, we devised a test-bench able to reproduce, in a scaled manner, the 3D illumination that the Ingot will face at the ELT, in order to validate the design and to perform preliminary tests of phase retrieval.