We present a tracking interferometer with an intrinsic compensation of the refractive index of air. By using both wavelengths of a frequency doubled Nd:YAG laser the refractive index of air can be determined and compensated by the dispersion. One dimensional benchmark verification experiments in air conditioned and typical harsh, uncontrolled environment show an asymptotic length dependent uncertainty in the order of 0.1 μm/m for distances over 10 m, proofing the potential of this approach for high accuracy measurements in industrial environments.

The trend in many fields of enabling technologies, such as microelectronics, communications, microsystems, and micromechanics, toward imposing increasingly stringent demands upon precision continues. Those types of technologies allow creating micromechanical components having dimensions of a few micrometers that have to be accurately measured, positioned relative to one another, and assembled. In that conjunction, laser-interferometric metrology provides unique opportunities that combine measurements over large ranges at extraordinarily fine resolutions with traceability of measurement results to international length standards. Laser-interferometric metrological systems may be used for measuring displacements ranging from subnanometers to several meters, without need for reconfiguring the optical or electronic systems involved or their component devices.

In summer 2011, two new laser strainmeters about 26.6 m long were installed in N-S and E-W directions parallel to an existing quartz tube strainmeter system at the Geodynamic Observatory Moxa, Thuringia/Germany. This kind of installation is unique in the world and allows the direct comparison of measurements of horizontal length changes with different types of strainmeters for the first time. For the comparison of both data sets, we used the tidal analysis over three years, the strain signals resulting from drilling a shallow 100 m deep borehole on the ground of the observatory and long-period signals. The tidal strain amplitude factors of the laser strainmeters are found to be much closer to theoretical values (85%-105% N-S and 56%-92% E-W) than those of the quartz tube strainmeters. A first data analysis shows that the new laser strainmeters are more sensitive in the short-periodic range with an improved signal-to-noise ratio and distinctly more stable during long-term drifts of environmental parameters such as air pressure or groundwater level. We compared the signal amplitudes of both strainmeter systems at variable signal periods and found frequency-dependent amplitude differences. Confirmed by the tidal parameters, we have now a stable and high resolution laser strainmeter system that serves as calibration reference for quartz tube strainmeters.

We present the optical simulation and design concept of a spatial heterodyne spectrometer (SHS) for mobile applications. A framework using Python and Zemax OpticStudio was developed for the optical system design and automated tolerance analysis from the incoming light, the spectrometer and the imaging lens system to the 2D detector. The spectrometer design and the fabrication methods were validated using a test setup in the VIS spectral range for a future SHS fabrication in the LWIR spectral band operating on small unmanned aerial vehicles (SUAV) for remote sensing applications.

This paper presents an application of the fiber coupled homodyne interferometers for the tide caused earth crust deformation measurements. Deformation of the earth crust mainly results from the tidal forces of sun and moon acting on the Earth, but also comes from seismic wave propagation or regional and local sources. The devices used for monitoring of such processes called strainmeters. The Geodynamic Observatory Moxa in Thuringia/Germany records and compares over the years the values gained by different stainmeters. The first laser interferometer was installed in the observatory in 2002. The new laser interferometer based setup, presented in this paper, allows direct monitoring of north-south and east-west components of the earth deformation in the range of 1-2 µm at measuring distances of 26 m.