Iodine-stabilized extended cavity diode laser at /spl lambda/=633 nm

An extended cavity diode laser at 633 nm has been frequency stabilized to I/sub 2/-Doppler-free absorption signals of the P(33)6-3 transition using a third-harmonic detection technique. The frequency was measured by the beat-frequency technique with an iodine-stabilized He-Ne laser as reference. A minimum value for the two-probe relative standard uncertainty of 1/spl times/ 10/sup -11/ (5 kHz) is reached after 100 s. We also report measurements of the hyperfine splittings of the P(33)6-3 transition and laser frequency dependence on modulation amplitude and iodine pressure.