Fresnel Drag in a Ring Laser: Measurement of the Dispersive Term

Abstract

The Fresnel drag has been measured in a triangular ring laser at a wavelength of 0.6328 \ensuremath{\mu}. The drag coefficient in fused silica is $\ensuremath{\alpha}=0.541\ifmmode\pm\else\textpm\fi{}0.003$, while the theory, including the dispersion term, gives ${\ensuremath{\alpha}}_{\mathrm{theor}}=1\ensuremath{-}(\frac{1}{{n}^{2}})\ensuremath{-}\ensuremath{\beta}(\frac{\ensuremath{\lambda}}{n})$ $\frac{\mathrm{dn}}{d\ensuremath{\lambda}}=0.5423$ with $\ensuremath{\beta}=1$. The coefficient $\ensuremath{\beta}$ is thus determined as $\ensuremath{\beta}=0.87\ifmmode\pm\else\textpm\fi{}0.22$, which includes the classical value $\ensuremath{\beta}=1$. Thus the magnitude of the drag in a ring laser is within the errors equal to that given in an inertial frame of reference (linear drag).