Recommendation 1 of the 16th CCL (2015)

Updates to the list of standard frequencies

The Consultative Committee for Length (CCL),

considering that

a common list of “Recommended values of standard frequencies for applications including the practical realization of the metre and secondary representations of the second” has been established;

the CCL-CCTF Frequency Standards Working Group (WGFS) has reviewed several candidates for updating the list;

recommends

that the following transition frequencies shall be included in the list of recommended values of standard frequencies:

• Absorbing molecule ¹²⁷I₂, saturated absorption a₁ component, R(36)32-0 transition.
  
  The values
  f_a1 = 564 074 632.42 MHz
  
  λ_α1 = 531 476 582.65 fm
  
  with an estimated relative standard uncertainty of 1 × 10⁻¹⁰ apply to the radiation of a frequency-doubled diode DFB laser, stabilized with an iodine cell external to the laser.


• Absorbing atom ⁸⁷Rb crossover between the d and f hyperfine components of the saturated absorption at 780 nm (D2 transition)
  
  The values
  f_{d/f crossover} = 384 227 981.9 MHz
  
  λ_{d/f crossover} = 780 246 291.6 fm
  
  with an estimated relative standard uncertainty of 5 × 10⁻¹⁰ apply to the radiation of a tunable External Cavity Diode Laser, stabilized using the 3rd derivative technique.

Note: The value of the standard uncertainty is assumed to correspond to a confidence level of 68 %. However, given the very limited number of available data there is a possibility that in hindsight this might not prove to be exact.

and asks the CIPM for approval.

DOI : 10.59161/CCL2015REC1E