| Fourier transform infrared spectrometer(FTIRS)has many advantage,such as high throughput,multi-channel,exact wave number,low stray light and good repeatability,which is widely applied in food monitoring,gas detection,bomb detection,mineral exploration,space mission,medical diagnosis,ocean exploration,quality and process control.We propose a static and light FTIRS based on stepped mirrors and light beam splitter.By introducing two stepped mirrors into the interference system,the optical path difference is discretized and the 2 Dimensional sampling of the interferogram is obtained.By introducing the light beam splitter into the interference system,the volume and weight are decreased.Therefore,the system has the advantages of compact and simple structure,stable performance,and good repeatability.The research work of the light FTIRS interference system is mainly carried out,the main research are as follows:(1)The design and fabrication of a low stepped mirror is studied.A method involving multiple depositions accompanied by a 50% reduction in thickness at every iteration is proposed.The technological process is developed,the key technology is introduced,and the 32-stages low stepped mirror is successfully produced.The test results show that the roughness is 1.72 nm and the average step height is 626.9nm,which meets the requirements of the system.In order to improve the spectral resolution,we fabricate a low stepped mirror consisting of 128-stages and with a step height of 625 nm by wet etching.(2)We analyzed the influence of the flatness error on the recovery spectrum using both theory and simulations.The analysis shows that the deformation of the step surface of the low stepped mirror will lead to a degradation of the spectral curve,drift of the peak position and a broadening of the spectral curve.And for the same deformation,it becomes more serious as wave-number increases.The experimental results show that with the increase of the thickness of the substrate,the drift of the spectral curve is reduced,the noise is weakened.When the substrate thickness of the low-stepped mirror is 5 mm,the drift of spectral curves is negligible and there is no double peak in the 3~5 ?m band.(3)The structure error of the stepped mirrors is analyzed.Stepped mirrors as the core optical devices of spectrometer,its step height consistency and structure's precision determine the spectral sampling interval and noise of system.The effect of the height error on the recovered spectrum is analyzed using Monte Carlo method.In order to reduce the influence,two methods are proposed.One is through tooling factor to reduce the monitoring error of the film thickness,thus reduce the height error.The other is using the least-squares approximation cosine polynomial algorithm to correct spectrum.The spectrum-constructing error is reduced to 2.34%,which meets the requirements of spectral restoration.(4)Design and fabrication of light beam splitter is studied.Two light beam splitters of grid beam splitter and bar beam splitter are proposed,which solves the difficult problem of large volume and heavy weight of the traditional beam splitter,and realizes the lightening and miniaturization.The material selection,process research and structural parameter design of two beam splitters were carried out.The high-accuracy grid beam splitter and the bar beam splitter were fabricated by anisotropic wet etching. |
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