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nanotimes News in Brief

10-10/11 :: October/November 2010

Optics // Ultra-precise Optical Systems for Space

excellent trueness of shape and hitherto unattained positional accuracy. The mirrors have been built for an infrared sounder telescope.

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“We wanted to simplify this complicated and time- consuming adjustment process,” says Scheiding. In the research project initiated by the German Aerospace Center (DLR) the scientist has therefo- re developed an innovative production technique which takes into account the later alignment of the components right from the outset. For this purpo- se, the individual mirror surfaces are positioned in relation to each other as precisely during processing as they will be later in the telescope. This reduces to a minimum the errors and corrections made when the mirrors are being fitted. The assembly process is simple and reproducible.

“The trick is that we mount all the mirrors for a module in the same machine at the same time and assign them to a common system of coordinates. To this end, each mirror blank is provided with defined, ultra-precise measurement marks and reference surfaces,” explains Scheiding. These fixed marks em- body the system of coordinates for diamond turning of the mirror shapes. At the same time, however, they fix the position of each mirror in relation to the adjacent mirrors. Finally they also serve as reference points for subsequent measurement processes to check the quality of the optical system.

new production technique enables complex optical surfaces to be manufactured with

The M2/M3 assembly with two exactly aligned aspherical mir- rors from the IRS-Tel reflecting telescope was produced with extremely high precision by using additional reference marks. © Fraunhofer IOF

The IOF demonstrates the degree of precision that can be achieved by such reference structures on the example of a mirror arrangement for an infrared sounder telescope (IRS-TEL). It incorporates two mirror modules, each of which has two juxtaposed aluminum mirror surfaces. The shape of the metal mirror deviates only 126nm from the ideal aspherical shape and the position of two mirrors in relation to each other is ten times more precise than for com- parable conventionally produced mirror assemblies. “As a result we can make optical systems of this type to a far greater degree of accuracy, but at the same time we’re cheaper because the time-consuming adjustment process during final assembly is no longer required,” says Scheiding. http://www.iof.fraunhofer.de/index_e.html