ATOMIC EMISSION LINES AS WAVELENGTH STANDARDS FOR THE 1- TO 6-MICRON REGION: CURRENT SITUATION

$^{1}$ Curtis J. Humphreys and Edward Paul, Jr., Program of Atomic Spectroscopy, Argonne National Laboratory, p 22 (1961). $^{2}$ Curtis J. Humphreys and Edward Paul, Jr., NOLC Report 464, NAVWEPS Reports 7190 and 7205. $^{3}$ Curtis J. Humphreys and Edward Paul, Jr., Program of the Optical Society of America, Abstract TB 11, Washington, D. C., March 1961. $^{4}$ E. Paul, Jr. and Curtis J. Humphreys, J. Opt. Soc. An 51, 1465A (1961), NAVWEPS Report 7205. $^{5}$ Curtis J. Humphreys and Edward Paul, Jr., HAVWEPS Report 7214.Author Institution: U. S. Naval Ordnance Laboratory, Corona, CaliforniaThe subject is reviewed in the light of developments during the three-year period following a presentation under a similar title at this symposium in 1959. These developments include actions of international commissions, or work performed under the sponsorship of these bodies, and new interferometric wavelength determinations that have the effect both of increasing the number of available standards and the range of coverage. The noble atmospheric gases are regarded as the most useful source elements for the production of atomic line-emission standards in terms of number and wavelength distribution of lines, absolute accuracy of wavelength determinations, and adaptability of available sources to observing requirements. Fairly $recent^{1,2}$ establishment of the values of the 2s and 3d levels (Paschen notation) of Ne I and Ar I by interferometric measurements in the lead sulfide region, taken in conjunction with precise knowledge of the other low levels of the s-, p- and d-series, obtained previously from photographic interferometric measurements, has permitted calculation of several hundred wavelengths as Ritz Combinations. These calculated wavelengths are of absolute accuracy comparable with the original interferometric determinations. They include nearly all lines of significant intensity in routine scans. Ritz Combinations of greater wavelength at least as far as $6\mu$ are expected to be practical with appropriate detectors. Recent interferometric determination of the 4f combinations of Ar $I^{3}$ has made available several additional lines, of which about ten are intense. The strong lines of natural krypton in the 1- to 2-micron region have been $re-observed^{4}$ by our interferometric technique, making more than 20 standards available. New observations are to be made using $Kr^{86}$ sources. The possibility of interferometric observation of the intense 2p-3d combinations in Xe I beyond $3\mu$ has been demonstrated, but the problem of dispersion of phase change at reflection has delayed precise establishment of wavelengths. Other possible sources of standards, including Ge I,$^{5}$, will be discussed