WIVERN: a laboratory experiment for testing novel laser-based wavefront sensing techniques

WIVERN is a testbed for laboratory experiments in laser-based wavefront sensing. It emulates laser uplink from a 4m telescope with 1.6 arcsec seeing and laser back-scattering from up to 20 km. Currently there are three current wavefront sensing capabilities. The first two are from a wide-field of view (1.0 arcmin) Shack Hartmann wavefront sensor observing a constellation of point sources at infinity (reference targets, star-oriented wavefront sensing), or an image from emulated back-scattering (wide-field correlation wavefront sensing). The third is based on the PPPP concept. Other sub-systems are laser projection replicating a pupil launch, a 7x7 pupil-conjugate deformable mirror (DM), and a wide-field camera for PSF analysis. A 500 Hz rate accumulates sufficient data for statistical and machine-learning analysis over hour timescales. It is a compact design (2.1m2) with mostly commercial dioptric components. The sub-system optical interfaces are identical: a flat focal plane for easy bench reconfiguration. The end-to-end design is diffraction-limited with ≤ 1% pupil distortion for wavelengths λ=633–750 nm

CUBES: application of image slicers to reformat the field for two spectral resolving powers

The Cassegrain U-Band Efficient Spectrograph (CUBES) is a high-efficiency spectrograph designed for observations from 305 to 400nm. It will be integrated at a Cassegrain focus of the Very Large Telescope (VLT). The image slicer technology is applied to reformat the field of view reducing the spectrograph entrance slit etendue and minimising the spectrograph volume and weight without slit losses. Two image slicers will provide CUBES with two spectral resolving powers: R≥20,000 for high resolution (HR) and R≥5,000 for low resolution (LR). Both image slicers are composed of two arrays of six spherical mirrors. For the HR mode, a rectangular field of view of 1.5arcsec by 10arcsec is reorganised into a slit of 0.19mm × 88mm; for the LR mode, a field of view of 6arcsec by 10arcsec is reformatted into a slit of 0.77mm × 88mm, with slicer mirrors of width 0.5mm and 2mm, respectively. CUBES is currently in the Preliminary Design Phase (Phase B). This communication presents the Conceptual (Phase A) design and the main performance for the HR and LR image slicers addressing the following technological challenges: compact layout with the minimum number of optical components to optimise throughput, near diffraction limited optical quality, telecentric design with overlapped exit pupils for all slices of the field of view, distribution of the slicer mirrors to reduce shadows and selection of the best substrate for the very short wavelengths at which CUBES will operate

WIVERN: a laboratory experiment for testing novel laser-based wavefront sensing techniques

WIVERN is a testbed for laboratory experiments in laser-based wavefront sensing. It emulates laser uplink from a 4m telescope with 1.6 arcsec seeing and laser back-scattering from up to 20 km. Currently there are three current wavefront sensing capabilities. The first two are from a wide-field of view (1.0 arcmin) Shack Hartmann wavefront sensor observing a constellation of point sources at infinity (reference targets, star-oriented wavefront sensing), or an image from emulated back-scattering (wide-field correlation wavefront sensing). The third is based on the PPPP concept. Other sub-systems are laser projection replicating a pupil launch, a 7x7 pupil-conjugate deformable mirror (DM), and a wide-field camera for PSF analysis. A 500 Hz rate accumulates sufficient data for statistical and machine-learning analysis over hour timescales. It is a compact design (2.1m2) with mostly commercial dioptric components. The sub-system optical interfaces are identical: a flat focal plane for easy bench reconfiguration. The end-to-end design is diffraction-limited with ≤ 1% pupil distortion for wavelengths λ=633–750 nm