Recommendation 2 of the 11th CCL (2003)

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 list of recommended radiations 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;
• femtosecond comb-based frequency measurements for certain iodine gas-cell standards on the subsidiary recommended source list have recently been made for the first time, leading to significantly reduced uncertainty;

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

• updated frequency values for the single trapped ⁸⁸Sr⁺ ion quadrupole transition and the single trapped ¹⁷¹Yb⁺ ion octupole transition;
• an updated frequency value for the C₂H₂-stabilized standard at 1.54 µm;
• updated frequency values for the I₂-stabilized standards at 543 nm and 515 nm.

Part b

The Consultative Committee for Length,

considering that:

• the 2001 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 2003 and is available on the website of the International Bureau of Weights and Measures (BIPM);
• the number (five) of proposed changes to the values already contained within the list is small;
• no new radiations are suggested;

proposes that:

• these changes be incorporated into the recommended radiations’s database maintained on the BIPM website in a manner which highlights the updated values relative to the 2001 list;
• these changes also be published as a short supplementary report in Metrologia.

Furthermore, considering that:

• there are a significantly increased number of frequency measurements, from both femtosecond comb measurement and laser heterodyne comparisons, for the important iodine-stabilized 633 nm He-Ne and 532 nm Nd:YAG standards;
• it is not necessary to change the recommended values for these radiations on account of issues related to I₂-cell reproducibility;

proposes that

• updated values for the global mean of the totality of frequency values resulting from BIPM.L-K11 key comparison for the 633 nm and 532 nm standards be maintained by the BIPM in accessible form;
• the recommended operating conditions for the 532 nm standard be:
  • cold point temperature (−15 ± 1) °C*;
  • frequency modulation width, peak-to-peak (1.0 ± 0.2) MHz (for 3f detection cases);
  • saturating beam intensity (17 ± 11) mW cm⁻².

Part c

The Consultative Committee for Length proposes that the International Committee for Weights and Measures adopt the following updated values for existing recommended radiations:

Part I of the list

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

The values

    f = 194 369 569 385 kHz

    λ = 1 542 383 712.37 fm

with a relative standard uncertainty of 5 × 10⁻¹¹, 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:

• C₂H₂-pressure range from 1.3 Pa to 5.3 Pa;
• frequency modulation width, peak-to-peak (1.5 ± 1.0) MHz* (for 3f detection cases);
• one-way intracavity beam power density of (25 ± 13) W cm⁻².

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

The values

    f = 444 779 044 095.5 kHz

    λ = 674 025 590.863 1 fm

with a relative standard uncertainty of 2.2 × 10⁻¹³, apply to the radiation of a laser stabilized to the transition observed with a trapped and cooled strontium ion. The values correspond to the centre of the Zeeman multiplet.

Absorbing ion ¹⁷¹Yb⁺, ² S_1/2 (F = 0, m_F = 0) – ² F_7/2 (F = 3, m_F = 0) transition

The values

    f = 642 121 496 772.3 kHz

    λ = 466 878 090.060 7 fm

with a relative standard uncertainty of 1.6 × 10⁻¹², apply to the octupole transition after correction for the ac Stark shift and second-order Zeeman shift.

Part II of the list

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

The values

    f = 582 490 603 442 kHz

    λ = 514 673 466.368 fm

with a relative standard uncertainty of 1.8 × 10⁻¹¹, apply to the radiation of a laser stabilized to an external iodine cell 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 .

Absorbing molecule ¹²⁷I₂, b₁₀ component, R(106) 28-0 transition

The values

    f = 551 580 162 400 kHz

    λ = 543 515 663.608 fm

with a relative standard uncertainty of 4.5 × 10⁻¹¹, apply to the radiation of a laser stabilized to an external iodine cell and subject to the following conditions:

• cold point temperature (0 ± 2) °C;
• frequency modulation width, peak-to-peak (2.0 ± 0.5) MHz.

* In this Recommendation, for the specification of operating conditions such as temperature, modulation width and laser power, the symbols ± refer to a tolerance, not to an uncertainty.

DOI : 10.59161/CCL2003REC2E