Toward interferometry for dimensional drift measurements with nanometer uncertainty

High-end industrial equipment evolves toward ever higher accuracies, and dimensional drift phenomena appear as a limitation for the required uncertainty level of precision metrology instrumentation. Detailed knowledge of the drift stability on timescales from minutes to weeks is needed for materials and constructional elements such as glued or bolted connections. We investigate a balanced, double-sided heterodyne interferometer for dimensional stability measurements. The complete interferometer includes an integrated refractometer and aims for a measurement uncertainty better than 100 pm. Measurements with a preliminary test setup of the instrument performance show an intrinsic stability of ±0.6 nm peak-to-peak over 23 h and 30 pm noise level at a timescale of a minute and shorter, limited by thermal and air refractive index fluctuations. Considerable improvement is expected for more stable ambient conditions and with dedicated, custom-made components.