Karl G. Kessler

Wave-Lengths of Mercury 198

The wave-lengths of 26 visible and ultraviolet radiations from H80198g have been measured to eight figures relative to 5460.7532A, provisionally adopted for the green line. A water-cooled electrodeless lamp containing two milligrams of artificial H80198g served as a light source when excited with radio waves of 100 Mc frequency. This lamp illuminated a Fabry-Perot interferometer and a large quartz spectrograph with which the interference patterns were photographed. Measurements of these patterns yielded relative wave-lengths with probable errors usually less than 0.0001A. In addition to demonstrating that H80198g 5460.7532A provides a practically perfect primary standard of length, this paper presents preliminary values of 27 superior spectroscopic standards which show that differences among vacuum wave numbers recur within the accuracy of the measurements, and that all the existing dispersion curves for air are incorrect.

Large-Aperture Grating Spectrograph Utilizing Commercial Camera Components*†

A compact, large-aperture spectrograph utilizing commercially available optical components has been designed and constructed. Light is admitted through an adjustable bilateral slit and is collimated by a 300-mm f/4.5 telephoto camera lens. The dispersive element is a 102 × 102 mm, 600-lines per mm plane reflection grating with a first-order blaze at 1.0 μ. The spectrum is photographed with a single-lens reflex 35-mm camera equipped with a 75-mm f/1.5 lens. One frame covers a spectral range of approximately 8000 A with a dispersion of about 200 A/mm in the first order.

Kr 86 and Atomic-Beam-Emitted Hg 198 Wavelengths

Vacuum wavelengths are given for the Hg198 2537- and 3132-A lines and the Kr86 6013- and 5651 A lines, referred to the Kr86 primary standard line 6057 A. The light sources were an Hg198 atomic-beam and a Kr86 hot-cathode lamp. A vacuum Fabry-Perot interferometer was employed for the measurements. The wavelength of the Hg198 3132 A line was also determined by using the Hg198 2537-A line as the reference standard. The accuracy of measurement of the Hg198 lines is about a factor of 5 higher than that of the Kr86 lines.

Sealed-Off Hg 198 Atomic-Beam Light Source

A sealed-off atomic-beam light source which utilizes the single isotope Hg198 is described. The emitted 2537 A line was investigated interferometrically with Fabry-Perot interferometers. Interferograms are shown for retardations of 0.4, 1.53, and 2.04 m with order numbers 1.6, 6.0, and 8.1 million, respectively. For each retardation, the theoretical contour of the observed fringes is shown. Theoretically predicted fringe contours are shown for retardations up to 6 m, the approximate limit of interference. It is concluded from the interferograms that the Hg198 2537 A line has a half-width of 0.0016 cm−1, as compared to 0.012 cm−1 for the Kr86 6056 A line proposed as the new primary standard of length. Owing to the small half-width and the extremely low level of pertubation in the atomic beam, this Hg198 line would be suitable for the primary standard of length.

ANALYSIS OF ATOMIC SPECTRA WITH ELECTRONIC DIGITAL COMPUTERS

A method has been developed for the analysis of atomic spectra with high speed electronic digital computers. The conversion of wavelength in air to vacuum wave numbers, the search for spectral terms, and the construction of square arrays are performed by machine computation. These techniques are applied to the analysis of the arc spectrum of ruthenium.

Correction for Systematic Wavelength Shifts in Atomic Beam Devices

Light emitted or absorbed by atoms in an atomic beam is shifted in frequency relative to the frequency for a stationary atom if the light ray is not normal to the trajectory of the atom. The magnitude of this shift is calculated and several devices which correct for this effect are described. For photoelectric recording of interference fringes, complete compensation can be achieved. In the case of photographic recording, it is shown that the residual error is negligible.

The Optics Program in the Optical Physics Division at NBS

Optics has been an important part of the research programs at the National Bureau of Standards since its first laboratories began operating in 1904, and we appreciate the opportunity to present to the readers of Optical Engineering some samples of our current work in optics.

Wavelengths of Mercury 198

The international standard of length, a platinum‐iridium bar located in a vault at the International Bureau of Weights and Measures near Paris, was measured relative to the wavelength of the red cadmium line by Michelson in 1892, and the value he derived for the wavelength of the red cadmium radiation has been provisionally adopted as the international standard of length.