Experimental Methods of Determining the Photoelastic Constants

  • T. S. Narasimhamurty


The earliest attempts to study quantitatively the change of the optical properties of solids under the influence of a mechanical stress were made by Neumann [871]. He described the optical changes in amorphous solids by introducing two constants p and q. These constants (which may be called the strain-optical constants due to Neumann) are defined in terms of a linear strain, say ε zz , thus:
$$\Delta n_z = n_z - n = - n^2 q\varepsilon _{zz} ,\,\Delta n_x = n_x - n = - n^2 p\varepsilon _{zz}$$
Here p and q relate the strain ε zz to the change produced by it in the index of refraction for light vibrations perpendicular and parallel to the direction of the linear strain; n is the refractive index of the solid in its undeformed state. It is the difference (pq) that can be determined using a Babinet compensator. Their individual values can be determined by interferometric methods, though not to a high degree of accuracy. The ratio p/q can be determined by ultrasonic methods (Bergmann and Fues [107]; Hiedemann and Hoesch [514–516]), and combining the values of (pq) and p/q, one can get the individual values of p and q.


Elliptic Vibration Biaxial Crystal Dark Fringe Photoelastic Constant Brillouin Component 
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Copyright information

© Plenum Press, New York 1981

Authors and Affiliations

  • T. S. Narasimhamurty
    • 1
  1. 1.Osmania UniversityHyderabadIndia

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