Rugged optical mirrors for Fourier transform spectrometers operated in harsh environments

摘要

The Total Carbon Column Observing Network (TCCON) and the Network for theDetection of Atmospheric Composition Change (NDACC) operate a number ofFourier transform spectrometers (FTSs) that measure trace gases in theatmosphere by observing solar spectra. To guide the sunlight into the FTS,a solar tracker has to be placed outside. This device needs high-qualityoptical mirrors with good reflectance in the near and mid-infrared.More and more FTS stations are operated in remote locations with harshenvironments. Optical mirrors are usually made for laboratory conditions andmight not last very long there. At the TCCON site on Ascension Island whichis operated by the Max Planck Institute for Biogeochemistry (MPI-BGC),several mirrors from different optical manufacturers were destroyed withinweeks.To continue operation, the MPI-BGC had to develop rugged mirrors that couldsustain the harsh conditions for months or even years. While commerciallyavailable mirrors are typically made from a substrate covered with a thinreflective coating, these rugged mirrors were made from stainless steel withno additional coating. Except for their lower reflectance (which can easilybe compensated for), their optical properties are comparable to existingmirrors. However, their rugged design makes them mostly immune to corrosionand scratching. Unlike most coated mirrors, they can also be cleaned easily.