Research on birefringence optical path difference superimposition by photo-elastic principle and spectrometric method

Wilhelm's law of stress optics establishes the relationship between stress and refractive index in elastic birefringence effect, and the relationship between birefringence optical path difference (BOPD) and principal stress under uniaxial stress can be given according to it. BOPD can be measured and calculated based on photo-elastic principle and spectrometric method, and now the measurement system of BOPD has been designed and realized for getting quantitative result. In the previous research work of the laboratory, BOPD of single acrylic sample with internal stress was measured and analyzed for evaluating internal stress level, however, there were few studies involving BOPD superimposition issue. BOPD superimposition has been studied by means of the measurement system including quarter wave plate, and it not only can give BOPD result of acrylic sample but also help determine whether internal stress is tensile or compressive after uniaxial stress direction is identified. BOPD superimposition can give more useful information on internal stress. The theoretical analysis of BOPD superimposition is discussed, the verification is illustrated and the application of BOPD superimposition in acrylic sample testing is introduced in this article.