<title>Experimental study of vibration measurement based on laser frequency splitting principle</title>

Abstract

A new method of measuring vibration is presented based on HeNe laser frequency splitting phenomenon and a series of experiments have been done. While a quartz ciystal wedge which vibrates with the vibration of measured object is inserted to a HeNe laser cavity, each laser mode is spliued to two orthogonal laser modes with a frequency diffence. The variation of the frequency difference is proportional to the displacement of the quartz wedge so that the frequency difference is modulated by vibration displacement signal. The vibration signal is demodulated to electrical signal through a photo -electric detector and signal processing circuit. A computer is used to adopt and analyze the vibration signal. By the system a l5nm resolution and 28nm repeatability of vibration amplitude are obtained. The method has a good potential prospective to be applied in high resolution, low and middle frequency vibration measurement or random vibration measurement.Keyword: Vibration measurement, Laser frequency splitting Background IntroductionVibration measurement is still an important subject in industry and scientific research though a lot of related technology is highly developed. Some problems remain to be solved, for example the performance of low and high frequency vibration still not satisfies various requirement.The study of measurement of microdisplacement has been done based on laser frequency splitting technology and has got a high resolution of 1Omn11 [2] [3J As a reasonable extending, the new method for measuring vibration is presented. The principle of measuring displacement is to utilize a HeNe laser with an intracavity quartz ciystal wedge. The variation of beat frequency, which called the laser frequency splitting, is proportional to the displacement of the wedge. if the intracavity quartz crystal wedge is vibrated, the laser beat frequency will be modulated by the vibration displacement. The vibration signal could be demodulated from optics signal.Because the frequency difference of the laser is of high sensitivity to displacement of the quartz wedge the vibration measurement method is of high resolution to amplitude. The experimental study has been done and its results is reported in this paper. Principle and scheme of experimentThe principle scheme is shown in Fig. 1 . A laser longitudinal mode is split into two orthogonal frequencies(modes) by the birefringence effect of an intracavity quartz crystal wedge Q. One mode is ordinary light and another is extra-ordinary light. The magnitude of frequency splitting, i.e. frequency difference of the o mode and e mode, is proportional to the difference of optical path lengths of the two modes which is proportional to the displacement of the wedge crossing the intracavity laser beam way.The relationship between frequency difference A(iv) and vibration displacement X can be represented by SPIE Vol. 3558 • 0277-786X1981$1O.OO Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/24/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx A(Av) = (n(9)...