For absolute length and form measurements at a large working distance (>150 mm) two special interferometers, a tandem interferometer and a Michelson interferometer with achromatic polarizing optics are constructed. In our experiments, both consist of a combination of one low-coherence interferometer and one laser interferometer. For the low-coherence interferometer part, a simple white-light source with less than 100 µW optical power output is chosen. It bases upon a low-cost fiber-coupled near-infrared LED with a large spectral width (FWHM > 68 nm at 825 nm). The use of achromatic polarizing optics such as broadband polarizing beamsplitters and achromatic quarter-wave plates in the low-coherence interferometer parts increases the contrast level of the white-light signal fringe pattern to nearly 100%. Furthermore, the fringe pattern in a polarized interferometer has no subsignatures and is unique. Hence, different algorithms are tested for signal processing and automated zero-point detection of the white-light signature. The software for an automated measurement is tested in a standard room without thermal control and without damped oscillation. Therefore, in experiments with the tandem interferometer, it was possible to measure the zero-point position of a white-light signature with a peak-to-peak difference of 154 nm under uncontrolled environmental conditions without thermal stabilization. The white-light Michelson interferometer with polarizing achromatic optics allows zero-point detections with a standard deviation (mean value) of less than 15 nm. The drift is proved through measurement results.

Background In this paper, we try to shed light on the question whether natural disasters, such as nuclear accidents, have an impact on policy makers’ activity in passing new green energy policies. Disruptive moments like exogenous shocks reinforce society’s disapproval against polluting technologies and should open a window of opportunities to eventually initiate a change toward green energy. Methods Based on the data of 34 OECD countries, we disentangle the effect of disruptive exogenous shocks on countries’ policy activity. Starting with OLS regressions, we run several robustness checks by using a pre-sample mean approach, an ARDL technique called dynamic heterogeneous panel models (DHPM), which allows for the distinction between long- and short-run effects. Results The results corroborate the hypothesis that unexpected, disruptive events have a positive impact on the actual number of renewable energy policies. The fade-out time for shocks is about 7 years, leaving a positive long-term effect. Conclusion Exogenous events such as nuclear disasters act as “focusing event” and seem to offer policy makers a window of opportunities to initiate conducive policy measures toward a cleaner economy. Furthermore, a country’s capacity in green technologies is key to a pervasive diffusion of green technologies.

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