Analysis and experimental study of low-stepped mirror in light FTIRS

Abstract

The structural parameters of low-stepped mirror which is the core component of a light Fourier transform infrared spectrometer (FTIRS) have important influence on the performance of the instrument. A simple method of multiple deposition is proposed to fabricate a low-stepped mirror with step height of 625 nm, for its high precision, high efficiency and miniaturization. So the film stress will be introduced in the process of coating, which can lead to step deformation. We build a bending model of the low-stepped mirror and analyze the influence of its deformation. The light intensity and spectrum are changed by the step deformation. Therefore, the film stress should be reduced in order to ensure the accuracy of the spectral information. Increasing the thickness of substrate is proposed in this paper to reduce the step deformation, besides adjusting the coating temperature and adding sub-layer. Our results reveal that the basic requirements of the system are satisfied when the thickness of the substrate is 5 mm in the appropriate coating environment. An FTIRS based on stepped mirrors and grid beam splitter is assembled and corresponding experiment is carried out to obtain the spectrum curve of acetonitrile.

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