Refractive index of liquids at high pressures

In this age of laser technology, the importance of studies on piezo– and elasto‐optic properties of liquids cannot be over-emphasized. In many applications such as acousto‐optic modulators, acoustic probes, high speed optical scanners and deflectors, etc., in the field of communications, a precise knowledge of the elasto‐optic coefficient of the liquids would be of immense help in the proper choice of the suitable acousto‐opticmaterials, as well as in the various design considerations. Besides being of immediate use in the various applications mentioned above, precise determinations of the piezo‐optic and elasto‐optic coefficients for liquids have a special importance in relation to the theory of optics. It is well known that the Lorentz‐Lorenz refraction formula does not accurately give the refractive index of a liquid in terms of the index for the vapor; the deviations from the formula are even more striking when we consider the changes in the refractive index of a liquid produced by changes of temperature or pressure. The explanation of these failures is a matter of considerable interest, and various attempts have been made to formulate theories giving better results. It is obvious that reliable experimental data regarding variations of refractive index under precisely defined physical conditions would be of value in testing such theories, and especially in determining the extent to which the refractivity of a dense fluid is a function of temperature independently of any changes in volume. Furthermore, it appears that these measurements can also be used to critically evaluate the various equations of state for liquids.