Uncertainty in Frequency Measurements at 88 THz Made with the NRC Frequency Chain: Frequency of the NRC HeNe/CH4Laser

Improvements to the NRC HeNe/CH 4 laser have produced a stable infrared source at 88 THz suitable for checking the stability of the CO 2 laser frequencies in the NRC phase-locked frequency chain. About 30 000 1 s average readings of the 88 THz laser frequency were obtained over the period 89-03-29 to 91-05-10. The Allan deviation σ y (1 s) of each CO 2 laser frequency in the chain was determined to be less than 2,5 × 10 -12 (82 Hz), when a new NRC hydrogen maser was used as a reference. The standard deviation of the mean of samples containing between 592 and 1 390 1 s average readings of the HeNe/CH 4 frequency, obtained on a given day, ranged from a fractional value 7,1 × 10 -14 to 3,0 × 10 -13 . The weighted standard deviation of 34 determinations of the HeNe/CH 4 laser frequency, obtained at various times over this period, was 73 Hz (8,3 × 10 -13 ), and the mean frequency relative to the frequency derived from the International Atomic Time scale (TAI) was 88 376 181 599 431(73)Hz. Other tests showed no significant systematic errors in the phase-locked CO 2 laser frequencies.