Optical Heterodyne Measurement of Xenon Isotope Shifts

Isotope-shift measurements with a precision of two parts in ${10}^9$ of the optical transition frequency were made for the $2.02-\mu$ line of the three even isotopes of xenon: ${\mathrm{Xe}}^{132}$, ${\mathrm{Xe}}^{134}$, and ${\mathrm{Xe}}^{136}$. This shift is extremely small due to the large xenon mass, the proximity of the xenon isotopes to the neutron magic number $N=82\mathrm{}$, and the weak interaction of the nucleus with the $5d$ and $6p$ electron states. The measurements were 500 ± 300 kHz (0.17 ± 0.01 × ${10}^{-3\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$) for ${\mathrm{Xe}}^{132}$-${\mathrm{Xe}}^{134}$ and 1500 ± 300 kHz (0.050 ± 0.01 × ${10}^{-3\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$) for ${\mathrm{Xe}}^{134}$-${\mathrm{Xe}}^{136}$, where the lighter isotope had the larger transition frequency in each case. These two shifts are sufficiently different to suggest that nuclear field effects contribute to the results.