Very Large Telescope Interferometer - Delay Line project
The Delay Lines are designed and built by Dutch Space of the Netherlands in cooperation with TNO.
The Telescopes are placed on the top of the 2650 m Cerro Paranal in the centre of the Atacama Desert in Chile. The location is chosen because of its ideal conditions for astronomical observations. The place is extremely dry, far away from any light pollution from cities and cloudless for 360 days of the year.
The Delay Lines will be used to combine the signal of two or more telescopes simultaneously, thereby creating an image with a resolution of upto 15 times the resolution that can be obtained with a single large telescope.
This will open up the possibility for spectacular astronomical discoveries in the near future.
The Delay Lines need to equal the path of the light from the star that is observed. Due to the angle of observation and the continuous rotation of the earth, the optical path difference can be as large as 120 m.
The principle of operation is shown in the figure below (courtesy of ESO).
Principle of interferometry with two telescopes and delay line (© ESO)
Therefore, the Delay Lines are placed in long underground tunnels in the mountain. The light of the telescopes are fed into the tunnel via a system of mirrors and lenses. Each telescope uses one Delay Line. The Delay Line is equipped with a retroreflector, the Cat's Eye. The Cat's eye needs to be positioned within a few nanometers.
The Delay Line uses a two-stage control system, based on linear motor technology, combined with high accuracy piezo-electric control elements. This enables the system to position the cat's eye reflector system with an accuracy of only a few nanometers over a length of 60 metres.
The control principle is shown below (courtesy of Dutch Space).
Control logic of the VLTI Delay Line (© Dutch Space)
The general layout of the Delay Line carriage is shown below (courtesy of Dutch Space).
Overall VLTI Delay Line carriage layout (© Dutch Space)
The Cat's Eye with the optical path of the science beam (© TNO)
With thanks to the European Southern Observatory (ESO), Dutch Space, TNO, and Mill House Consultancy.
More information on the VLTI Delay Line project:
http://www.eso.org/outreach/press-rel/pr-2001/pr-06-01.html
http://www.eso.org/outreach/press-rel/pr-2000/phot-26-00.html