Some Aspects of the Refractive Behavior of Gases

  • Daniel Bershader


When compressibility effects are present in fluid flow fields, the variation in density produces a corresponding change in optical refractivity. Two aspects of this behavior have been exploited in experimental gas dynamics, especially during the past 25 years. The first of these relates to the angular deflection of light in the presence of a transverse refractivity gradient. Starting from Fermat’s Principle one can show in a straightforward manner (Ref. 1) that, given a medium in which the refractive index n is an arbitrary function of the coordinates, then the radius of curvature R of a light ray at any point (x,y,z) is given by
$$\frac{1}{R} = grad\ log n.\mathop e\limits^\to $$
where e⃗ is a unit vector perpendicular to the light path. This relation is the basis of the well-known schlieren and shadow techniques, now widely used in laboratory studies of fluid dynamic phenomena.


Complex Refractive Index Optical Path Difference Fringe Shift Photon Echo Negative Dispersion 
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Copyright information

© Plenum Press, New York 1971

Authors and Affiliations

  • Daniel Bershader
    • 1
  1. 1.Stanford UniversityUSA

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