Speed of Light from Direct Frequency and Wavelength Measurements of the Methane-Stabilized Laser

Abstract

The frequency and wavelength of the methane-stabilized laser at 3.39 \ensuremath{\mu}m were directly measured against the respective primary standards. With infrared frequency synthesis techniques, we obtain $\ensuremath{\nu}=88.376181627(50)$ THz. With frequency-controlled interferometry, we find $\ensuremath{\lambda}=3.392231376(12)$ \ensuremath{\mu}m. Multiplication yields the speed of light $c=299792456.2(1.1)$ m/sec, in agreement with and 100 times less uncertain than the previously accepted value. The main limitation is asymmetry in the krypton 6057-\AA{} line defining the meter.