Investigation On Optical Properties Of CSBN Crystals Based On Michelson Interferometer And Digital Image Processing

Calcium doped Strontium barium niobate crystals grown by the Institute of Crystal Materials of Shandong University of China, which molecular formula is (Ca0.28Ba0.72)x(Sr0.60Ba0.40)1-xNb2O6 and short for CSBN, are ferroelectric and photoelectric crystals having the structure of ferroelectric tetragonal tungsten bronze-type. The elementary 45 atoms cell of CSBN has tetragonal system with the space group P4bm. According to different x values in the molecular formula of CSBN, CSBN crystals can be divided into three types, CSBN25 (x=0.25), CSBN50 (x=0.5) and CSBN75 (x=0.75).Part of optical properties of CSBN50 crystal, including refractive index and photorefractive effect, using Michelson interferometer and digital image processing methods, are mainly performed in this paper. The detail contents are listed as following:1) Using Michelson interferometer, stepper motor rotary table, CCD camera, an experimental platform which mainly used for refractive index measurement of transparent materials was built. The stability of this platform was tested and CSBN50's birefringence was measured. Refractive index is an important optical parameter of crystals. It is also a basic item of evaluation of crystals'physical properties. There are many methods to measure crystals'refractive index. However, the range and accuracy of these methods are restricted by their corresponding requirements. Interferometry with high precision and no destructive is attracting more and more interest in recent years. In this paper, stepper motor rotary table and CCD camera are integrated into Michelson interferometer system and compose an experimental platform of measuring refractive index of transparent materials. Based on this platform, this paper presents a method of measuring CSBN's refractive index.2) A new Michelson interferometer compensation method was investigated to modify refractive index using digital image processing technology.3) Improved experimental platform to investigate photorefractive effect of CSBN50 crystal based on digital image processing method. Photorefractive effect is the phenomenon that the crystals'refractive index changes with imposed optical frequency electric field. In recent yeas, investigation of crystals'photorefractive effect gets increasing interest. This paper studies the behavior of refractive index changes with polarized light written-in and read-out while external electric field is imposed or not imposed. The following conclusions were obtained:(1) Under laser irradiation (wavelength 632.8nm and power 1.5mW), CSBN50's photorefractive effect does not change significantly in 80 minutes without external electric field. (2) Under external electric field along optical axis, CSBN50's photorefractive effect is significant with following characteristics. (a) The bigger the external electric field is, the greater the refractive index changes. (b) Refractive index change directions of e-polarization and o-polarization are the same. (c) E light refractive index is more significant than o light refractive index. (d) Reversing the direction of external electric field CSBN50's refractive index changes in the opposite direction.