Download the CIPM list of recommended radiations complete with source data and related transitions

– or – Select wavelength...    237 nm  (In+) 243 nm  (H) 282 nm  (Hg+) 436 nm  (Yb+) 467 nm  (Yb+) 515 nm  (I2) 532 nm  (I2) 543 nm  (I2) 576 nm  (I2) 606 nm  (Kr) 612 nm  (I2) 633 nm  (I2) 640 nm  (I2) 657 nm  (Ca) 674 nm  (Sr+) 698 nm  (Sr) 778 nm  (Rb) 1.54 µm  (C2H2) 3.39 µm  (CH4) 10.3 µm  (OsO4)      (Spectral lamp)

This list replaces that published in Metrologia, 2003, 40, 103-133 and partially revised in Metrologia, 2005, 42, 323-325.

Latest revisions:
October 2005	282 nm	436 nm	515 nm
	657 nm	674 nm	698 nm
	778 nm	1.54 µm
October 2003	467 nm	532 nm	(674 nm)
	(515 nm)	543 nm	(1.54 µm)

Following a Recommendation of the CCL in 2003 (Recommendation 2c) and its approval by the CIPM in the same year (Recommendation 1 (CI-2003)), the current revised list of recommended radiations is given here. Also provided are the source data used in estimating the wavelengths, frequencies and uncertainties of the recommended radiations.

The CIPM acknowledges the considerable effort put into the preparation of this list by the Consultative Committee for Length (CCL) through its Working Group on the Mise en Pratique (WGMeP), which includes representatives of national metrology institutes and the BIPM. A significant part of the work was related to the estimation of the uncertainties of the values given in the list of recommended radiations, and the CIPM draws attention to this as an example of the importance of making proper estimates of uncertainty in reporting the results of all metrological work.

The list of recommended radiations was first published by the CIPM in 1983 (CI-1983, Recommendation 1) in the mise en pratique of the definition of the metre. This specified that the metre should be realized by one of the following methods:

1. by means of the length l of the path travelled in vacuum by a plane electromagnetic wave in a time t; this length is obtained from the measured time t, using the relation l = c₀ · t and the value of the speed of light in vacuum c₀ = 299 792 458 m s^–1,
2. by means of the wavelength in vacuum of a plane electromagnetic wave of frequency f; this wavelength is obtained from the measured frequency f using the relation = c₀/f and the value of the speed of light in vacuum c₀ = 299 792 458 m s^–1,
3. by means of one of the radiations from the list given here, whose stated wavelength in vacuum or whose stated frequency can be used with the uncertainty shown, provided that the given specifications and accepted good practice are followed.

Notes:

In this list, the values of the frequency f and of the vacuum wavelength should be related exactly by the relation f = c0, with c0 = 299 792 458 m s–1, but the values of are rounded. The data and analysis used for the compilation of this list are set out in the associated source data for each recommended radiation. It should be noted that for several of the listed radiations, few independent values are available, so the estimated uncertainties may not reflect all sources of variability. Some of the listed radiations can be replaced, without degrading the accuracy, by a radiation corresponding to another component of the same transition or by another radiation, when the frequency difference is known with sufficient accuracy. Such radiations are listed in the associated tables of absolute frequency of the other transitions related to those adopted as recommended and frequency intervals between transitions and hyperfine components. It should also be noted that to achieve the uncertainties given here it is not sufficient just to meet the specifications for the listed parameters. In addition, it is necessary to follow the best good practice concerning methods of stabilization as described in numerous scientific and technical publications. References to appropriate articles, illustrating accepted good practice for a particular radiation, may be obtained by application to a member laboratory of the CCL or to the BIPM.