Precision interferometry based on highly stable laser sources at 633 nm

• Applicant: Dr. Ulrike Blumröder
• Subject Area: Measurement Systems
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 542290024

The rise of nanotechnology in industry and research poses enormous challenges for manufacturing and characterisation methods. Novel structural design concepts and the development of complex-shaped high-precision optics require three-dimensional, traceable structural measurements that ensure accuracies in the nanometre range. High-precision, traceable positioning systems that increasingly have to map structures down to the (sub)-nanometre range on macroscopic measurement areas are indispensible for these applications. Interferometry is one of the primary and most accurate methods for the practical realisation of the metre definition. Thus incremental, interferometric measurement systems usually form the basis of position determination in these systems. The reduction of uncertainty contributions of interferometric measuring systems is therefore of great importance. A decisive uncertainty contribution is the absolute accuracy and frequency stability of the laser sources used in interferometric measurement systems. Due to the high bandwidths and complexity of multi-channel measuring systems the highly dynamic length measurement used in nanometrology puts special demands not only on the frequency stability of the vacuum wavelength but also on the available output power and power stability of the corresponding laser source. By stabilising laser systems to a single line of an optical frequency comb, it is possible to link optical frequencies to highly accurate frequency standards commonly used for the practical realisation of the SI unit second with a relative uncertainty ≤ 10-12 to create traceable, highly stable optical frequencies for precision interferometry. However, in order to benefit from the high accuracy of the time base very long integration times are required. This is in contradiction to the requirements of the highly dynamic interferometric measurements used within nanopositioning. The research project therefore aims to transfer the low uncertainty of a laser source referenced to the SI second by means of an optical frequency comb achievable for long integration times into the millisecond range decisive for dynamic interferometric length measurements as used within nanometrology. This will be accomplished by combining ultra-low-noise laser sources with a GPS-referenced frequency comb and will guarantee the traceability of the vacuum wavelength at a level of at least 10-12 independently of the integration time considered. In particular, the practical requirements of multi-channel, fibre-coupled interferometric measurement systems are to be taken into account. Finally, the developed approach will exemplarily be integrated into a six-axis, fibre-coupled interferometer system of a nanopositioning and nanomeasuring machine with a macroscopic measuring range of 200 mm x 200 mm x 25 mm.

• DFG Programme: Research Grants