Recommendation 2 of the 14th CCL (2009)

Updates to the list of standard frequencies

The Consultative Committee for Length,

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 (FSWG) has reviewed several promising candidates for inclusion into the list,
• the CCTF at its session in June 2009 has already recommended new values for the same reference frequencies;

recommends

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

• the unperturbed optical transition 5s^{2 1}S₀ – 5s 5p ³P₀ of the ⁸⁷Sr neutral atom with a frequency of 429 228 004 229 873.65 Hz and a relative standard uncertainty of 1 × 10⁻¹⁵.

This radiation is already endorsed by the CIPM as a secondary representation of the second.

• the unperturbed optical transition 5s^{2 1}S₀ – 5s 5p ³P₀ of the ⁸⁸Sr neutral atom with a frequency of 429 228 066 418 012 Hz and a relative standard uncertainty of 1 × 10⁻¹⁴.
• the unperturbed optical transition 4s ²S_1/2 – 3d ²D_5/2 of the ⁴⁰Ca⁺ ion with a frequency of 411 042 129 776 393 Hz and a relative standard uncertainty of 4 × 10⁻¹⁴.
• the unperturbed optical transition ²S_1/2 (F=0) – ²F_7/2 (F=3, m_F=0) of the ¹⁷¹Yb⁺ ion with a frequency of 642 121 496 772 657 Hz and a relative standard uncertainty of 6 × 10⁻¹⁴.
• the unperturbed optical transition 6s^{2 1}S₀ (F=1/2) – 6s 6p ³P₀ (F=1/2) of the ¹⁷¹Yb neutral atom with a frequency of 518 295 836 590 864 Hz and a relative standard uncertainty of 1.6 × 10⁻¹³.

DOI : 10.59161/CCL2009REC2E