Electric Birefringence and Dichroism in Critical Binary Mixtures

In near-critical fluids the critical fluctuations interact via a dipolar interaction in stationary electric field and the structure factor becomes uniaxial. As a result electric birefringence and dichroism are enhanced on approaching to criticality. A general formula for the effects is presented in the steady case for arbitrary wavelength of probing light. Another formula for transient electric birefringence can well explain a nonexponential decay observed by experiments. The nonlinear dielectric constant in stationary field is also calculated.