Equality of X-Ray and Light Scattering Measurements of Coherence Lengths at the Nematic-Smectic- A Phase Transition

We have measured by light scattering the divergence of the elastic constants K₂ and K₃ at the nematic-smectic-A transition in the liquid crystals 8OCB, -8S5, and 8CB over a reduced temperature range 10^-5<t<10^-2. We find critical exponents ν_∥ and ν_⊥ and power-law coefficients ξ_∥⁰ and ξ_⊥⁰ which agree with values obtained from x-ray scattering within experimental error.