Individual Sphere Coating at METAS in Bern/Switzerland
About the Project
As far as we know, METAS houses the currently largest integrating sphere in Europe with a diameter of (3.98 ± 0.01) m, i.e. almost 4 metres. This sphere has now not been actively used for measuring tasks for several years because the coating of the manufacturer at the time has yellowed slightly over the decades. This is typical for older barium sulphate coatings. This process is accelerated by higher humidity, for example, to name just one factor.
In the course of the refurbishment of the sphere, the sphere was therefore recoated directly on site by a specialist from Gigahertz. For this purpose, Gigahertz-Optik pre-produced more than 70 litres of a special barium sulphate coating with the desired 90 percent reflectance in a complex and absolutely reproducible manufacturing process. The large quantity is required for a sphere with a diameter of 4 m and many coating layers for a very high homogeneity.
At METAS, work was carried out for this purpose in a vacuum tent specially erected for the coating in order to ensure cleanliness in the calibration laboratory there and not to endanger other sensitive optical equipment such as a mirror goniometer. Here, the preparation by METAS was outstanding! Due to the sphere size, the unique coating technique was a special challenge. The coating and the associated work on the integrating sphere took a week. Sphere specialist Anton Henger (Gigahertz Optik GmbH) and Florian Stuker (METAS) worked closely together on this project to achieve an optimal result and pave the way for further sphere construction.
The Swiss Federal Institute of Metrology METAS is the federal government's centre of competence for all matters relating to measurement, measuring equipment and measurement procedures. As Switzerland's national metrology institute, it ensures that measurements can be made in Switzerland with the accuracy and reliability required for the economy, research, society and environmental protection. METAS is the Swiss equivalent of the Physikalisch-Technische Bundesanstalt (PTB) in the Federal Republic of Germany or the National Institute of Standards and Technology (NIST) in the USA, to name but two others.
METAS is responsible for ensuring the metrological infrastructure and for the development and application of high-precision measurement procedures and methods. Some of METAS' most important tasks include the calibration and testing of measuring instruments, the development of standards and technical regulations, the implementation of metrological research projects and the provision of metrological services to industry and the public. It performs calibrations and tests in areas such as electricity, magnetism, optics, thermodynamics, time and frequency, mass and length.
METAS works closely with international partners to ensure the international comparability of measurement results. In this project, we worked together with the Radiometry and Photometry group.
Left: Coating of the integrating sphere with protective equipment. Right: The sphere was prepared by METAS in a vacuum tent to protect the sensitive measuring equipment in the laboratory.
At a Glance
- Europe's largest integrating sphere with a diameter of 4 m was coated
- An individual reflectance of 90 % was achieved here
- High homogeneity due to multi-layer application
- A successfully implemented project thanks to very good cooperation