Technologies that have been developed or extended in collaboration with industry through an ESO development contract or collaboration agreement

Cooled IR optics The supply of machined metal optical elements for cryogenically cooled instruments has traditionally been limited to US manufacturers. The French firm REOSC/SAGEM, well known for the manufacture of glass optics, had no experience in this field and were unable to bid for ESO tenders. Through an ESO development contract placed with REOSC, and close co-operation with ESO experts, REOSC is now able to deliver excellent cryogenic optics.
VolumePhase Holographic Gratings Since Volume Phase Holographic Gratings were first proposed for astronomy in 1998, they have had major impact on astronomical spectroscopy in terms of their intrinsic high efficiency and versatility, reduced polarisation and scattering. The original VPHGs were produced for Raman Spectroscopy but these were small and not ideally suited for astronomy.

A facility to manufacture large Volume Phase Holographic Gratings was set up at the Centre Spatial de Liège. ESO has led a consortium of five astronomical institutions that allowed ten prototype gratings to be manufactured up to 30 cm in size. The Centre Spatial de Liège has since created a spin-off company that is the leading European supplier of VPH gratings and currently has the world's largest facility for the manufacture of these gratings.

Peel-off cleaning technique for telescope mirrors Following discussions with Bayer AG about ESO's requirements for cleaning telescope mirrors, Bayer developed a trial product which they believed would meet ESO's requirements. ESO tested this product on various surfaces and sent the results back to Bayer. After four additional experimental iterations, a product was finally selected for commercial production.

The resulting peel-off cleaning product, "XL Clean 5", is produced commercially by IRSA Lackfabrik GmbH.

Photonic crystal fibres An important technology pioneered at ESO is the use of optical fibres to transmit high power visible laser beams, and this is a key element in the ESO Laser Guide Star Facility concept. However, a fundamental problem using classical mono-mode optical fibres is due to Stimulated Brillouin Scattering (SBS), a non-linearity which severely limits the laser power that can be transmitted through the fibre. Photonic Crystal fibres ("holey fibres"), which were first demonstrated in the laboratory by researchers at Bath University in 1996, offer an ingenious solution to overcoming SBS to a large degree. Working initially with Crystal Fibre A/S in Denmark, ESO promoted the development of fibres with characteristics suitable for the LGSF wavelength of 598 nm and with good optical transmission to demonstrate the feasibility of this technology. Since then, production fibres have been manufactured by Crystal Fibres and also by Mitsubishi which meet ESO's requirements.

Fibre optic transmission of the laser beam leads to a significant reduction in the cost, system complexity and maintenance requirements compared to rival technologies. ESO's developments have been followed with great interest by other laser guide star projects as well as industry because of the wider commercial implications, for example in the telecommunications industry and the medical field. As a next step, ESO is currently working on the application of hollow-core photonic crystal fibres to the LGSF, which are now becoming available.

Laser Cleaning of large optical surface The techniques of using UV lasers to clean optical surfaces were known but not well adapted to the in situ cleaning of large surfaces, such as telescope mirrors.

An ESO study and development contract allowed Laser Laboratorium Göttingen to develop the technique to be applied to large optical surfaces in non-laboratory environments.

AO System Technology In 1989, ESO unveiled the first non-military Adaptive Optics system on a large telescope. The Come-On system, developed through collaboration between ESO, ONERA and astronomical institutes and firms in France, was put into service on the ESO 3.6 m telescope, and was followed by a succession of upgrades, starting with Come-On-Plus and then ADONIS.

During this period, and continuing with the development of the AO systems for the VLT (NACO, MACAO, SINFONI, CRIRES etc.) a number of firms received ESO contracts for developing the key technologies.

Dichroic beam splitters Although there are many dichroic beam-splitters on the commercial market, standard dichroics do not provide optimum performance for many Adaptive Optics systems. ESO therefore commissioned SAGEM to produce dichroics optimised for this application. Apart from supplying VLT Adaptive Optics projects, SAGEM has also produced dichroics for the Gran Telescopio Canarias project.
Strip Tape Encoders When ESO originally approached the world's major manufacturer of high-precision strip encoders, Heidenhain in Germany, they could not guarantee that the specification for the VLT encoders could be met. Moreover, the tape mounting technique used at the time involved a complex mechanical arrangement to ensure that the tension in the tape was always constant and uniform. Through a development contract, ESO asked Heidenhain to produce an internally mounted tape encoder, and provided them with a full-sized VLT Adapter bearing for tests. The results of this development were so conclusive — in terms of both improved accuracy and simplified mechanics — that this subsequently became the standard way of mounting high precision strip encoders.