Application Of Ultrasonic Wave In The Analysis Of Laser Modes

Early in the nineteen thirties have began to research the acoustoopticinteraction, but each level of diffraction optical frequency shift and deflectionangle produced by ultrasonic grating diffraction is very small, a long timeacoustooptic interaction has not been widely applied. Because the laser beamis monochromatic, unidirectional, high brightness and the energy of the laserbeam can be focused in a small footprint and so on, it’s frequency, phase,amplitude and intensity could be modulated by the acousto-optic devices. Theadvent of the laser leads acoustooptic interaction theory widely practicalapplication.When the acousto-optic medium passed by ultrasound, it’s refractiveindex will be affected by the strain modulation and changes periodically,equivalent to a grating. when the laser passed by this acousto-optic medium itwill be diffracted, it’s spectrum is made up of light carrier frequency and sidefrequency. According to this principle, we found that when Naman-Nathdiffraction occurs and the laser has multi-longitudinal modes, we can adjustthe ultrasonic frequency and parameters to make a diffraction leveloverlapping of adjacent longitudinal modes, then we could accuratelycalculated the frequency difference of the laser longitudinal mode.This paper studies the characteristics of laser longitudinal mode usingacousto-optic interaction theory and phenomena. When the laser pass by leadmolybdate medium and interferometer, it’s spectrum distribution map couldbe displayed by the oscilloscope. Analysis of the frequency spectrum, weresearch out some characteristics of laser longitudinal mode.The main worksare as follows:1. Deduce the sound waves and light waves coupled wave equations,theoretically expound the waves exist two kinds of diffraction type lights, expound the distribution characteristics of the two kinds of diffraction light,observe Naman-Nath spectrum distribution map, determine frequencydifference of adjacent level of diffraction when the light impacted by theultrasonic traveling wave.2. Research on the ultrasonic type in acousto-optic medium, findfrequency difference of adjacent level of diffraction are different when thelight waves after ultrasonic traveling wave and standing wave effect, then putforward the method of distinguish ultrasonic traveling wave and standingwave by measuring the frequency domain.3. Research on longitudinal mode of laser which are different cavitylength, observe polarization properties of three modes and four modesoperation laser output directly into the interferometer. And study the fourmodes laser device, let the emitted laser which after the effect ofacousto-optic device enter the interferometer, compare of the polarizationproperties whether or not are changed after the affect of acousto-opticinteraction.4. Study of the longitudinal mode frequency difference of the laser,successfully overlap adjacent longitudinal modes of±2level diffractionspectrum, put forward an accurate method for measuring laser longitudinalmode frequency difference, present a new research method for the analysis oflaser modes.