It is intended to test thoroughly, in Europe, all the systems composing the AO Facility before delivery in Paranal. The AOD is convinced that this strategy was a key-element to the success of the commissioning of the first generation AO modules delivered by AOD.
ASSIST (Adaptive Secondary Simulator and Instrument Testbed) is a collaboration between NOVA (Nederlandse Onderzoekschool voor de Astronomie)(PI: Remko Stuik) and ESO
However, in the case of the AOF such strategy implies a serious challenge, the main one being how to design a Test Bench allowing the implementation of a 1.1 convex aspheric deformable mirror in the optical path !!! An ingenious solution was found by optical designer B.Delabre (ESO) and is now used as a baseline by the ASSIST developer team in Leiden.
ASSIST must provide a long and sophisticated list of functionalities:
- Use the DSM 1.1m convex mirror in the optical path
- provide a f/19.53 Nasmyth-like opto-mechanical I/F for the output focal plane
- provide a large FOV (2.5 arcmin)
- provide high optical quality at 2 wavelengths: 589 nm (laser beam) and 1.6 micron (scientific corrected wavelength)
- low pupil distortion (to insure a good match between actuator geometry on the DSM and the WFS apertures distribution)
- provide laser and natural light sources at the input focal plane, of variable intensity
- simulate turbulent wavefront in the whole field of view affected by a multi-layered turbulence at a level of 0.6 to 1.1" seeing
- be operated by a simple soft. GUI
Optical and Mechanical Design
The fundamental problem is that in order to test a 1.1m convex piece of optics, one needs an optical component > 1.1m. It already implies that the test setup will require a large volume and meter-telescope size optical components.
The Figure 1 shows this optical design. The component "AM1" is the main mirror and is a concave aspheric surface of 1.7m diameter. This is the heart of the test bench. A second smaller aspheric mirror (140mmdiameter) is located above , just below the surface of the DSM.Beam splitters/mirrors will allow to fold the beam on the side for the input and output focal planes.
Figure 1: ASSIST Optical Design
The mechanical implementation take the form shown on Figure 2.
Figure 2: Opto-Mechanical Implementation of ASSIST.
ASSIST Role & Functions
The following list describes the test and characterization processes that will take place and that ASSIST will allow to perform:
- Optical Tests of the DSM
- Setup and Alignment of the AO modules
- DSM Flattening, measure of the Influence Functions,characterization of the mirror stroke
- Interaction Matrix measurement and loop closure
- Investigation of the various IM calibration methods proposed and evaluation of their performance
- Chopping tests, Field Stabilization tests, focusing
- Mounting of test cameras for delivered image correction
- Pupil alignment and study of Command Matrix for GLAO and LTAO
- LGS and Visible/IR NGS acquisition
- AO performance optimization
The Final Design Review took place early July 09. The review should be closed by November 15th. The system will be in the manufacturing phase till end 2010.