Hyperfine splittings of two photon 5s -- 6s transitions of Rb

Using a single frequency tapered amplifier diode laser scanning around 993 nm in a Rb cell, we have conducted two photon Doppler free spectroscopy of $^{\mathrm{85}}$Rb and $^{\mathrm{87}}$Rb. Using a wavemeter, we have measured the splittings and absolute positions of the four $\Delta $F$=$0 hyperfine transitions from 5s to 6s to an accuracy of 0.001 cm$^{\mathrm{-1}}$. We are also measuring the dependence of the hyperfine splittings on laser power and on the presence of various values of an applied DC electric field.