Design Of Static FTIR Interferometer With Photoelastic-effect

Comparing with other spectrum detection strategies which have been used popularly in the field of spectrum detection, FTIR method has many advantages on the resolution power, spectrum range and sensitivity. The interferometer is the key part of the FTIR spectrum analyzer. Its performance and structure will determine the spectrum analyzer's performance. Based on the analysis and research of several structures of interferometer in paper, one static interferometer with photo-elastic effect has been designed. It has compact structure and fast modulation frequency.After learning the development of the interferometers all over the world, the advantages and defects of them are highlighted. FTIR interferometer with photoelastic effect has been chosen as the research direction combining the project requirement with status of technology development inside. Firstly, the author explains the optical or physical characters of crystal, photoelastic effect, structure of the photoelastic modulator and the method how to calculate the resonance frequency of photoelastic modulator. Then A dynamic model of resonance frequency-temperature has been made to analyze the instability of resonance frequency of the photoelastic modulator. A control loop model of resonance frequency-temperature also designed. This model is the guide for how to design the control circuit of photoelastic modulator.Finally, Based on the theory learning, a photoelastic modulator header has been designed using SeZn crystal and ceramic. Its resonance frequency is 125 KHz. A driver also be designed in laboratory. By experiments the phase retardation which is larger thanπhas been obtained. In other words, the optical path difference is larger than half of wavelength. The result has also verified related theory depicted in paper.