Stray-light Analysis Of Fourier Transform Infrared Spectrometer Based On Multistep Mirrors

Spectrometers are commonly used in physics, chemistry, biology and other basicsubject areas as well as practical areas such as agriculture and meteorology. In recentyears, in order to meet the real-time monitoring, portable infrared spectrometer needs,many countries have conducted research on micro-infrared spectrometer. Comparedwith other principles-based infrared spectrometer, Fourier transform spectrometer(FTS) with a multi-channel, high radiation flux and high precise wave number isusually preferred. Our group studied a spatial modulated Fourier transform infraredspectrometer (FTIR) based on multistep mirrors.For any optical system, in addition to the normal optical transmission path thestray light transmission path exists. When the stray light reaches the detector, theinstrumental performance would be affected. Therefore, it is necessary to analyze thestray-light level of the optical system and take steps to weaken its impact on systemperformance. This work is very important to achieve the desired design specifications.The FTIR developed by our group works in the infrared band, some of the features ofits own makes the stray light analysis particularly essential:1. Because of large refractive index of the materials working in the infrared band,the transmission rate is not high, bringing serious ghost images.2. Diffraction effects become more pronounced in the infrared band.3. Infrared radiation radiated by the mechanical surfaces must be considered asone of the sources of the stray light.The main work of this thesis is to analyze the stray-light level of the preliminarydesign of the FTIR and give the corresponding suppression measures. This thesisconsists of two parts:First, analyze the stray light caused by the edges of the multistep mirror facets using physical optical method.1. Using the scalar diffraction theory, program the diffraction calculationprograms to calculate the interferogram when diffraction is taken into account.2. Theoretically analysis the diffraction’s effects on the recovered spectrum andprovide a method to reduce the effect.Second, analyze the non-diffraction stray light using geometric optical method.1. Simulate and calculate some indicators to show the stray light levels of thesystem, including the point-source transmission and the stray radiation ratio.2. Classify the tray light transmission paths, give the major transmission paths ofthe stray light to provide the basis for proposing effective stray light suppressionmethods.3. Analysis the stray radiation caused by the mechanical faces of the system andgive quantitative results.4. Proposing effective stray light suppression methods.5. Verify the effectiveness of the suppression methods and compare the straylight levels of the system before and after suppression.Finally, give a summary of the overall content and look forward to the furtherwork.