The Reaearch About Matching Frequency Of Photoelastic Modulation Interference

Spectroscopy is widely used in environmental monitoring， food monitoring，aerospace，biomedical，and military fields，The Fourier transform spectroscopy which basedon photoelastic modulator (PEM) has characteristics of high modulation frequency，widespectrum，high sensitivity and anti-seismic capability，which has been applied to spectralmeaasurement field widely. The spectrometer made of using the spectrum technique, and itscore component is photoelastic modulation interferometer. And the performance ofinterferometer mainly been determined by piezocrystal and photoelastic crystal,whichconsistsed photoelastic modulator(PEM).When the frequency of the two components in PEMmatches better, the resonant amplitude and the optical difference will be greater, thedistinguishable ability of the interference would be stronger. In summary, it is significant todo detailed study with PEM in frequency matching.Firstly, on the basis of the research status at home and abroad, a detailed research of thetheory of characteristic frequency in mechanical vibration had been done combined with thespecial requirements of instrument. The main contain of research is the mechanical vibrationcharacteristic frequency theory under the exciting force of harmonic. MATLAB has been usedto simulate vibration displacement map near the resonant frequency, then a detaileddescription and experimental verification had been made. Secondly, a new theory which is tocalculated resonant frequency of unknown material is derived from the resonant frequency ofa known material and had verified by MATLAB and the multi-physics coupling analysissoftware (COMSOL Multiphysics) It has great guiding significance to actual measurement.Finally, the resonant frequency of ZnSe with measured dimensions has been calculated withthe theory. The size of the damped piezoelectric crystals has been calculated based on theresonant frequency. Finite element simulation of photoelastic crystal and piezoelectric crystalhas been done though COMSOL to verify the above results.Results showed that the allowable error range，characteristic frequency is very close to the simulation results with the theoretical value. And the software simulation， can only getclose to the value of the resonant frequency and the frequency close to the resonancefrequency，can appear the phenomenon of "beat frequence"，consistent with the experimentalresults，due to the presence of damping， the extension of time， finally reached steady state,the actual study of PEM has important guiding significance.