The Research On Stability Of Photoelastic Modulation Fourier Transform Spectrometer

As a newly developed spectrum measuring technology, photoelastic modulation Fouriertransform spectrometer (PEM-FTS) with high speed, high sensitivity and wide spectrum haspotential applications and development prospects in the transient spectral detecting fields suchas aerospace exploration, environmental monitoring, biological medicine, national defenseconstruction and so on. Photoelastic modulator is the core component of PEM-FTS, and itsmodulation efficiency become lower and optical path difference become instable during workprocess because of the heat dissipation. The variation above-mentioned is restricting themeasurement precision and stability of PEM-FTS. Wherefore, how to reduce the effect onstability of optical path difference of photoelastic modulator, how to make the PEM-FTSmaintain high measurement stability in the long work, are the important science problemsneed to be solved for researching on PEM-FTS.Based on the principles of photoelastic modulation Fourier transform spectroscopy andmulti-physics coupling characteristics, the paper makes study on the stability of PEM-FTS,and develops a high stability photoelastic modulation interferometer, together with its controlsystem.Firstly, the influence mechanism on the stability of photoelastic modulator caused bythermal dissipation is researched. The influence on vibration performance of photoelasticmodulator is analysed on account of vibration mode and the type of loss. Combining withtemperature and frequency drifting models of photoelastic modulator, the effect on qualityfactor and coupling characteristics is deduced caused by temperature rise for piezoelectricactuator and photoelastic crystal. The relationship between temperature rise and modulationefficiency and stability of optical path difference is got and verified through experiments. Theresults laid the theoretical basis and experimental evidence for research on stability ofPEM-FTS.Secondly, a design scheme of photoelastic modulator is presents coupled byanti-resonant, in order to reduce the temperature rise during processing. Based on theelectrostriction effect of piezoelectrics under high driving voltage, the quality factor andmodulation efficiency is compared between resonance coupled design and anti-resonancecoupled design. Then the effect on temperature rise of anti-resonance coupled design is analyzed, and its feasibility has been verified using the High voltage driver circuit developed.Thirdly, in order to eliminate the effect on stability of photoelastic modulationinterferometer caused by heat dissipation, a bandwidth coupled photoelastic modulator anddouble colsed-loop adaptive control system are developed on the basis of anti-resonancecoupled scheme. Taking the coupling characteristics and modulation efficiency as startingpoints, the paper analysis the functional relationship among initial offset frequency anddriving frequency, and establishes a stable control theory model including driving frequency,temperature rise and optical path difference factor. The hardware and program of controlsystem are also finished.Finally, a photoelastic modulation Fourier transform spectroscopy measurement platformis built by integrating the multiple-reflect way and bandwidth coupled, in order to verify itswavelength precision and measurement stability. The results show that the design schemeimproves the precision of PEM-FTS as70times as before.