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Division 4

Division 4 which is responsible for optics is home to three base units: that of length, time and luminous intensity. On this basis, standards and measuring methods of highest accuracy are developed for various optical quantities.



Division "Optics" supports industry, science and society by providing measurement services, research and development in the field of optical technology. Based on the SI units of length, time and luminous intensity different units are realized and disseminated. Further more, accurate standards and measurement techniques are developed.

The division realizes the time scale UTC (PTB), which is the legal time in the Federal Republic of Germany, performs precision measurements in different fields of optics and cooperates in international standardisation and certification.


The frequency instability and systematic uncertainty of the latest generation of optical atomic clocks is now approaching the one part in 1018 level. Comparisons between clocks must account for the relativistic redshift of the clock frequencies, which is proportional to the corresponding gravity (gravitational plus centrifugal) potential of the clocks. For contributions to international timescales, the relativistic redshift correction must be applied with respect to a conventional zero potential value, which is derived from the mean sea level or geoid.

To benefit fully from the uncertainty of the optical clocks, the gravity potential must be determined with an accuracy of 0.1 m2/s2, equivalent to 0.01 m vertical height. Two geodetic approaches were investigated in a European research project [1]: geometric levelling and the Global Navigation Satellite Systems (GNSS)/geoid approach. Geometric levelling gives potential differences...

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The "Young Scientist Award", endowed with 1000 euros, was awarded for the first time within the scope of the 9th High Level Expert Meeting "Asphere Metrology", hosted by the Competence Center Ultrapräzise Oberflächenbearbeitung (CC UPOB e.V.). This award is intended to nurture and honour young scientists working in the fields of ultra-precise surface finishing. The nominated candidates presented the results of their research to the audience of experts in the form of short lectures and a poster. Jan-Henrik Hagemann, a doctoral candidate from PTB's Working Group 4.22, "Flatness Metrology", won first prize for his work on the interferometric measurement of the form of optical surfaces with partly coherent multi-source illumination.

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