Standard frequencies - TITLE H1

Recommended values of standard frequencies

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All the radiations in the list (apart from the 87Rb 6.8 GHz and 176Lu+ 353.6 THz transition) may be used for the practical realization of the definition of the metre.

The information is available in PDF format below or in machine-readable form from our API service.

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Please also find the data associated with the 2021 and 2025 adjustments of standard frequencies.

Supplementary documentation for the 2021 calculation

Supplementary documentation for the 2025 calculation

info - s

The radiations marked [SRS] may be used as secondary representations of the second.

 

Procedure for updating the CIPM list of frequencies (CCTF 2017)

 

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Standard Frequency [SRS]

1267 THz  –  115In+
Wavelength ≈ 237 nm

Standard Frequency

1233 THz  –  H
Wavelength ≈ 243 nm

Standard Frequency [SRS]

1129 THz  –  199Hg
Wavelength ≈ 265 nm

Standard Frequency [SRS]

1121 THz  –  27Al+
Wavelength ≈ 267 nm

Standard Frequency [SRS]

1065 THz  –  199Hg+
Wavelength ≈ 282 nm

Standard Frequency [SRS]

688 THz  –  171Yb+
Wavelength ≈ 436 nm

Standard Frequency [SRS]

642 THz  –  171Yb+
Wavelength ≈ 467 nm

Standard Frequency

582 THz  –  I2
Wavelength ≈ 515 nm

Standard Frequency

564 THz  –  I2
Wavelength ≈ 531 nm

Standard Frequency

563 THz  –  I2
Wavelength ≈ 532 nm

Standard Frequency

552 THz  –  I2
Wavelength ≈ 543 nm

Standard Frequency

520 THz  –  I2
Wavelength ≈ 576 nm

Standard Frequency [SRS]

518 THz  –  171Yb
Wavelength ≈ 578 nm

Standard Frequency

495 THz  –  86Kr spectral lamp
Wavelength ≈ 606 nm

Standard Frequency

490 THz  –  I2
Wavelength ≈ 612 nm

Standard Frequency

474 THz  –  I2
Wavelength ≈ 633 nm

Standard Frequency

474 THz  –  unstabilized HeNe
Wavelength ≈ 633 nm

Standard Frequency

468 THz  –  I2
Wavelength ≈ 640 nm

Standard Frequency

456 THz  –  40Ca
Wavelength ≈ 657 nm

Standard Frequency [SRS]

445 THz  –  88Sr+
Wavelength ≈ 674 nm

Standard Frequency [SRS]

429 THz  –  87Sr
Wavelength ≈ 698 nm

Standard Frequency [SRS]

429 THz  –  88Sr
Wavelength ≈ 698 nm

Standard Frequency [SRS]

411 THz  –  40Ca+
Wavelength ≈ 729 nm

Standard Frequency

385 THz  –  85Rb
Wavelength ≈ 778 nm

Standard Frequency

384 THz  –  87Rb
Wavelength ≈ 780 nm

Standard Frequency

353.6 THz  –  176Lu+

Standard Frequency

194 THz  –  13C2H2
Wavelength ≈ 1.54 µm

Standard Frequency

88.4 THz  –  CH4
Wavelength ≈ 3.39 µm

Standard Frequency

29.1 THz  –  OsO4
Wavelength ≈ 10.3 μm

Standard Frequency

Spectral lamps

Standard Frequency [SRS]

6.835 GHz  –  87Rb