Fourier transform spectroscopy has established itself as the standard method for spectral analysis of infrared light. Here we present a robust and compact novel static Fourier transform spectrometer design without any moving parts. The design is well suited for measurements in the infrared as it works with extended light sources independent of their size. The design is experimentally evaluated in the mid-infrared wavelength region between 7.2 μm and 16 μm. Due to its large etendue, its low internal light loss, and its static design it enables high speed spectral analysis in the mid-infrared.
Instantaneous measurement of optical or geometrical parameters of thin layers is an ambitious aim in many industrial applications. These layers have a variety of use-cases, such as optical bandpassing, dielectric permittivity, or lubrication. Mostly, these layers are in motion due to the production process. In order to observe process parameters, the motion usually has to be disrupted. Thus, the increase of production time due to control purposes is an undesirable drawback of this otherwise suitable technique. In this publication, we present a solution to this particular drawback of most production process monitoring systems exemplarily for film thickness measurement. We show the realization of a measurement principle which has, to our knowledge, never been published before in this application. Therefore, we exploit the advantages of the combination of a linear variable filter with a complementary metal oxide semiconductor sensor array. By an apt readout sequence, this measurement system is able to measure transmission spectra while the target is in motion. We show that this measurement system is able to measure film thicknesses of objects in the range of several 100 nm thickness at up to a velocity of 4 m/s. A reproducibility below 2 nm was acquired.
A major part of future renewable energy will be generated in offshore wind farms. The used turbines of the 5 MW class and beyond, often feature a planetary gear with 1000 liters lubricating oil or even more. Monitoring the oil aging process provides early indication of necessary maintenance and oil change. Thus maintenance is no longer time-scheduled but becomes wear dependent providing ecological and economical benefits. This paper describes two approaches based on a linear variable filter (LVF) as dispersive element in a setup of a cost effective infrared miniature spectrometer for oil condition monitoring purposes. Spectra and design criteria of a static multi-element detector and a scanning single element detector system are compared and rated. Both LVF miniature spectrometers are appropriately designed for the suggested measurements but have certain restrictions. LVF multi-channel sensors combined with sophisticated multivariate data processing offer the possibility to use the sensor for a broad range of lubricants just by a software update of the calibration set. An all-purpose oil sensor may be obtained.
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