Light drag in a ring laser: An improved determination of the drag coefficient

The light drag in a rotating fused-silica disk inserted in a He-Ne ring laser was measured at $\lambda =633\mathrm{}$ nm and found to be ${\alpha }_e=0.5424\mathrm{}$ with an rms error ($1\sigma$) of ±2 × ${10}^{-4\mathrm{}}$, including the known error sources. This constitutes a tenfold improvement in accuracy over a previous result. While the given error margin does not include the value given by the Lorentz drag in a linear arrangement, ${\alpha }_{\mathrm{LO}}=0.54182\mathrm{}$, the measured difference of $2\sigma$ is deemed too small to claim a discrepancy.