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

The frequency and wavelength of the methane-stabilized laser at 3.39 μm were directly measured against the respective primary standards. With infrared frequency synthesis techniques, we obtain $\nu =88.376\mathrm{}181627\left(50\right)\mathrm{}$ THz. With frequency-controlled interferometry, we find $\lambda =3.392\mathrm{}231376\left(12\right)\mathrm{}$ μm. Multiplication yields the speed of light $c=299\mathrm{}792456.2\left(1.1\right)\mathrm{}$ m/sec, in agreement with and 100 times less uncertain than the previously accepted value. The main limitation is asymmetry in the krypton 6057-Å line defining the meter.