Research On Parameter Test Method Of Acousto-optic Crystal

Acousto-optic diffractive devices have many advantages such as light weight,small size,high power,good stability,high diffraction efficiency,and play an increasingly important role in people’s production,life,and military applications.Acousto-optic crystals are core component of acousto-optic diffractive devices.Testing their optical-electrical properties has an important value in analysis of acousto-optic crystals’quality,internal defect,service life,and improvement of production process.LiNbO₃ and TeO₂,excellent acousto-optic crystal materials,are widely used in many fields.In this paper,LiNbO₃ crystal and TeO₂crystal are used as main research objects.Measurement techniques of acousto-optic materials’basic parameters can be explored from a study of elastic-optic coefficients test method about LiNbO₃ crystal and TeO₂ crystal.At first,propagation characteristics of light in the crystal,elastic mechanical properties of the crystal,and stress-strain relationship of anisotropic crystals are discussed in this paper.Then,a calculation model of the elastic-optic effect is established by a method of refractive index ellipsoid of crystals.Based on theoretical analysis,the Mach-Zehnder interferometry method is designed to test elastic-optic coefficients of crystals.A force is exerted on an acousto-optic crystal by using a side rocking rotating frame with push-pull gauge,and a CMOS photoelectric sensor is used for data acquisition.Elastic-optic coefficientsπ₁₃ andπ₃₃ of LiNbO₃ crystal are measured by establishment of experimental devices,and their values are 6.21×10^-13,1.63×10^-13,respectively.At the same time,when measuring elastic-optic coefficientsπ₁₃ andπ₃₃ of TeO₂crystal,it is necessary to apply an external force to a crystal in[001]direction.For this case,internal stress and strain distribution of the crystal are simulated.The simulation results show that when an external force is applied to a crystal in[001]direction,internal stress and strain are evenly distributed except for a small part of edge portion of the crystal.When TeO₂ crystal is applied with an external force in[001]direction and a beam of light passes in[100]direction,elastic-optic coefficients of TeO₂ crystal are measured,and their values are 2.93×10^-12,2.00×10^-12,respectively.When TeO₂ crystal is applied with an external force in[001]direction and a beam of light passes in[010]direction,values of TeO₂ crystal’s elastic-optic coefficients are 2.86×10^-12,2.01×10^-12,respectively.Compared with LiNbO₃ crystal,TeO₂ crystal has a large order of magnitude.During experimental test,we can find that interference fringes of TeO₂ crystal move faster than LiNbO₃ crystal.Therefore,more interference images can be acquired with TeO₂crystal.The experimental data shows that when an external force is applied to a crystal,main refractive indexs of crystal change with a change of external force:The stress in crystal varies with an external force.Main refractive indexs n_o and n_e of crystal rise with the increase in stress,and the relationship between main refractive indexs and crystal stress is linear.Influence factors of experimental tests are also analyzed in this paper.Meanwhile,ANSYS finite element method is used to simulate internal stress and strain of TeO₂ crystal.There are two kinds of simulated crystals.One has a cutting direction of[100][010][001]with an external force applied in[010]direction,and the other has a cutting direction of[110][1（?）10][001]with an external force applied in[1（?）10]direction.The result of research makes a preparation for the future improvement of experimental devices and expansion of test range.