Projects & expertise of the Optical and Mechanical Systems department

SOM, the Optical and Mechanical Systems Department of IPAG, is mainly involved in design and analysis activities but also in system engineering and project management. Its fields of application cover all instrumental activities on the laboratory’s themes. The department works in close collaboration with the team CHARM, dedicated to instrumental research.

Adaptive optics is a technique that allows to correct in real time the deformations of the wavefront (aberrations) thanks to a front sensor, a computer and a deformable optic, most often a mirror.

Since the 1990s, the laboratory has been a major player in the development of instruments for the CFHT and the VLT. The mechanics of the WIRCAM instrument was developed by the mechanics of our department. For the Very Large Telescope of the ESO located in Paranal, Chile, the optics and mechanics team has largely contributed to the NACO project, an instrument running the Nasmyth Adaptive Optics System (NAOS) and the Near Infrared Imager and Spectrograph (CONICA). Together they constitute the first adaptive optics system to be installed on the Very Large Telescope.

Thanks to this experience, the laboratory has piloted the SPHERE project (High Contrast Spectro-Polarimeter dedicated to the Search for Exoplanets) for more than 12 years, on which, in addition to having developed the optics, the main bench and all the supporting structure, the laboratory has been the prime contractor of the system and has carried out the integration. The department is today involved in the development of SAXO+ which aims at adding to SPHERE a second stage of adaptive optics ultra fast in the infrared of pyramid type, which will make it possible to reach a better correction of the turbulences generated by the crossing of the light in the atmosphere. The department ensures the mechanical design of the SAXO+ assembly.

The department is also involved in adaptive optics on instruments for the ELT (Extremely Large Telescope), since it develops the laser star wavefront sensors for the MORFEO and HARMONI projects. In MORFEO, the department develops the complete subsystem of the sensors which includes the optical sensor (composed of a relay and its camera), a mounting plate making the whole turn, and a vertical translation plate. HARMONI will use the same detection module as MORFEO. In these two projects, the department is responsible for mechanical design, optical design, and system analysis.

The goal here is to detect and characterize extra-solar planets. These are angularly close to there host star and could be 1 million times fainter. We therefore need to develop techniques to remove or attenuate the flux of the main star to allow the detection and the characterization of the planet.

The department contributed first to the development of the EXTRA observatory, by developing the optics of the spectrograph, the fiber links and the mechanics of the fiber positioners. Based on 3 telescopes of 60cm, this observatory makes the planet detection by the method of transits.

Today the group is mainly involved in high contrast imaging in two areas:

• The ERC EXACT is an R&D program in which two of the components are dedicated to the definition and improvement of imaging techniques. The department provides a support role on this program.
• The development of the high contrast arm of the HARMONI project for the ELT. This system, based on an apodization, allows to create a dark zone around the star to detect planets 1 million times fainter than their star. On this project the department ensures four roles: mechanical development, optics, system and project management.

This technique aims at pointing several telescopes on the same stellar object, and at making the signals of the telescopes interfere with each other. While the angular resolution of a telescope is limited by the size of the diameter of the primary mirror, that of an interferometer is limited by the distance between the telescopes and can therefore be ten times greater.

The department has contributed to various programs for the VLTI (Very Large Telescope Interferometer) :

• PIONIER : a 4 telescope recombiner in the near infrared (1.4 to 1.8µm) installed in 2010 at VLTI and still in operation.
• GRAVITY and GRAVITY+: GRAVITY is a 4-telescope recombiner for the near infrared (2 to 2.45µm) installed in 2015 at VLTI. Like PIONIER, GRAVITY is based on the use of silica-on-silicon guided optics components. These components are the result of a research and development program carried out in particular with the LETI. The department has developed the guided optics components, the injection fibers and the mechanics to be integrated in the cryostat and to operate continuously at -80°C. GRAVITY+ is an ongoing program to extend the performance of GRAVITY by adding more efficient adaptive optics and a laser guide star on each telescopes. The department is also involved in GRAVITY+ by developing the support mechanics for the deformable mirrors.
  
  

Views of the adjustable mount of the Gravity+ deformable mirror

Spectrography consists in separating light into a frequency spectrum and recording the signal with a detector. The interpretation of the spectra allows to study the chemical or physical constitution of the stars (chemical composition, surface and internal temperature, radiated power...).

Several concepts are being studied in the department:

• ImSPOC is a family of compact hyperspectral imagers developed, within IPAG / OSUG, jointly by UGA and ONERA since 2016 in the context of Labex Focus and OSUG. The concept is implemented for the sciences of the Environment, Earth and Universe: measurement of greenhouse gases, atmospheric chemistry, monitoring of vegetation, sedimentation in rivers, planetology, monitoring of solar activity.
• VIPA is a high spectral resolution spectrograph (R=80 000) operating in the infrared (1.5 - 1.65µm). The concept of this spectrograph is based on a dispersive component called VIPA whose principle is close to a Fabry-Perot interferometer and a cross disperser (ruled grating) to separate the orders. The experiment is placed in a cryostat cooled at about 80K. This spectrograph is more dedicated to the characterization of extra-solar planets.

The department is also involved in various projects such as:

• The Cherenkov Telescope Array has its cameras based on the use of photomultipliers on which the collection of photons is optimized by adding a light collector on each ofd them. The optimization of these collectors has been done by an optician of the department.
• ASONG is a wavefront sensor developed in the framework of a maturation project with the Linksium incubator.

• VIPA: Experimental test of a 40 cm-long R=100 000 spectrometer for exoplanet characterisation
• ImSPOC
• CTA: Design of light concentrators for Cherenkov telescope observatories
• HARMONI at ELT: development of the high-contrast module
• GRAVITY+
• MORFEO