Design and Manufacture of Micro Interference System in Spatial Modulation Fourier Transform Spectrometer

Abstract

Spatial modulation Fourier transform spectrometer(FTS) based on micro step mirror arrays with high optical path difference sampling precision was a new high-tech measuring instrument. To depress the interferogram aliasing resulted from the chromatic dispersion of beam splitter, considering interferogram contrast reversal as the criterion of image degradation, the thickness difference between beam splitter and compensating plate was determined smaller than 0.2μm. So as to restrain the ghost images induced by secondary reflection on the surface of beam splitter, the transmittance of anti-reflection film should be more than 98% and the transmittance of beam splitter film should be controlled within (50±5) %. Since the restriction of processing method and machining accuracy to micro step mirrors, the thickness deviation and angle deviation existed between various sub-mirrors. After the error synthesis to sub-mirror errors using Monte Carlo method, the tolerance of the thickness deviation and angle deviation was controlled in 1μm and 2×10-5rad. Meanwhile, the step height deviation of micro step mirrors may induce non uniform sampling to interference signal. Thus a spectrum method by least-squares cosines progression arithmetic was advanced and the validity of which was demonstrated well.