Recommendation 1 of the 12th CCL (2005)

Revision of the Mise en Pratique list of recommended radiations

Part a

The Consultative Committee for Length,

considering that:

• improved frequency values for radiations of some high-stability cold ion standards already documented in the recommended radiations list have recently become available;
• improved frequency values for the infra-red gas-cell-based optical frequency standard in the optical telecommunications region, already documented in the recommended radiations list, have been determined;
• improved frequency values for certain iodine gas-cell standard, already documented in the subsidiary recommended source list, have been determined;
• frequencies of new cold atoms, of atoms in the near-infrared region and of molecules in the optical telecommunications region have been determined by femtosecond comb-based frequency measurements for the first time;

proposes that the list of recommended radiations be revised to include the following:

• updated frequency values for the single trapped ⁸⁸Sr⁺ ion quadrupole transition, the single trapped ¹⁹⁹Hg⁺ quadrupole transition and the single trapped ¹⁷¹Yb⁺ quadrupole transition;
• an updated frequency value for the Ca atom transition;
• an updated frequency value for the C₂H₂-stabilized standard at 1.54 µm;
• an updated frequency value for the I₂-stabilized standard at 515 nm;
• the addition of the ⁸⁷Sr atom transition at 698 nm;
• the addition of the ⁸⁷Rb atom two-photon transitions at 760 nm;
• the addition of the ¹²C₂H₂ (ν1 + v3) band and the ¹³C₂H₂ (ν1 + v3) and (ν1 + v3 + ν4 + v5) bands at 1.54 µm.

Part b

The Consultative Committee for Length,

considering that:

• the 2003 list of recommended radiations for the realization of the metre, including radiations of other optical frequency standards, was comprehensively reorganized and recently published in Metrologia 2005 and is available on the website of the International Bureau of Weights and Measures (BIPM);
• the number (six) of proposed changes to the values already contained within the list is small;
• only four new radiations are suggested;

proposes that:

• these changes be incorporated into the database’ recommended radiations maintained on the BIPM website in a manner which highlights the updated values relative to the 2003 list;
• these changes also be published as a short supplementary report in Metrologia.

Part c

The Consultative Committee for Length proposes that the CIPM adopt the following updated values for existing recommended radiations:

Part I of the list

Absorbing ion ⁸⁸Sr⁺, 5s ² S_1/2 – 4d ² D_5/2 transition

The values

    f = 444 779 044 095 484.6 Hz

    λ = 674 025 590.863 136 fm

with a relative standard uncertainty of 7 × 10⁻¹⁵ apply to the radiation of a laser stabilized to the unperturbed transition observed with a trapped and cooled strontium ion. The values correspond to the centre of the Zeeman multiplet.

Absorbing ion ¹⁹⁹Hg⁺, 5d¹⁰ 6s ² S_1/2 (F = 0) – 5d ⁹ 6s^{2 2} D_5/2 (F = 2), ∆_mF = 0 transition

The values

    f = 1 064 721 609 899 145 Hz

    λ = 281 568 867.591 968 6 fm

with a relative standard uncertainty of 3 × 10−15, apply to the unperturbed quadrupole transition of a trapped and cooled mercury ion.

Absorbing ion ¹⁷¹Yb⁺, 6s ² S_1/2 (F = 0, _mF = 0) – 5d ² D_3/2 (F =2, _mF = 0) transition

The values

    f = 688 358 979 309 308 Hz

    λ = 435 517 610.739 688 fm

with a relative standard uncertainty of 9 × 10⁻¹⁵, apply to the unperturbed quadrupole transition of a trapped and cooled ytterbium ion.

Absorbing atom ⁴⁰Ca, ¹S₀ – ³P₁; ∆_mJ = 0 transition

The values

    f = 455 986 240 494 140 Hz

    λ = 657 459 439.291 683 fm

with a relative standard uncertainty of 1.8 × 10⁻¹⁴, apply to the radiation of a laser stabilised to Ca atoms. The values correspond to the mean frequency of the two recoil-split components for atoms which are effectively stationary, i.e. the values are corrected for the second-order Doppler shift.

Absorbing molecule ¹³C₂H₂ P(16) (ν1 + ν3) transition

The values

    f = 194 369 569 384 kHz

    λ = 1 542 383 712.38 fm

with a relative standard uncertainty of 2.6 × 10⁻¹¹−11 apply to the radiation of a laser stabilized using the third harmonic detection technique to an external 13C2H2 cell within an enhancement cavity and subject to the following conditions:

• cell pressure (3 ± 2) Pa;
• frequency modulation width, peak-to-peak (1 ± 0.5) MHz;
• one-way intracavity beam intensity of (25 ± 20) W cm⁻².

Part II of the list

Absorbing molecule ¹²⁷I₂, a₃ component, P(13) 43-0 transition

The values

    f = 582 490 603 442 kHz

    λ = 514 673 466.367 fm

with a relative standard uncertainty of 8.6 × 10⁻¹² apply to the radiation of a laser stabilized with an iodine cell external to the laser, and subject to the following conditions:

• cold point temperature (-5 ± 2) °C, corresponding to a I₂ pressure of (2.4 ± 0.5) Pa;
• saturating beam intensity <40 mW cm⁻².

Part d

The Consultative Committee for Length proposes that the CIPM adopt the following radiation values for addition to the list of recommended radiations:

Absorbing atom ⁸⁷Sr, 5s^{2 1} S₀ – 5s 5p ³ P₀ transition

    f = 429 228 004 229 910 Hz

    λ = 698 445 709.612 694 fm

with a relative standard uncertainty of 2 × 10⁻¹³, apply to the radiation of a laser stabilised to Sr atoms.

Absorbing atom ⁸⁷Rb, 5S_1/2 (F_g = 2) – 7S_1/2 (F_e = 2) two-photon transition

    f = 394 397 384 460 kHz

    λ = 760 127 906.05 fm

with a relative standard uncertainty of 1.7 × 10⁻¹⁰.

Absorbing atom ⁸⁷Rb, 5S_1/2 (F_g = 1) – 7S_1/2 (F_e = 1) two-photon transition

    f = 394 400 482 100 kHz

    λ = 760 121 936.0 fm

with a relative standard uncertainty of 4.5 × 10⁻¹⁰. Acetylene transitions referenced by offset from the ¹³C₂H₂ P(16) (ν1+ ν3) recommended transition

• ¹²C₂H₂, (ν1 + ν3) band at 1.54 µm
• ¹³C₂H₂, (ν1 + ν3) and (ν1 + ν3 + ν4 + ν5) bands at 1.54 µm.

DOI : 10.59161/CCL2005REC1E