Abstract

Interferometrically measured wavelengths are given for 278 thorium lines in the range 2747–4572 Å. The light source is a liquid-nitrogen-cooled hollow-cathode lamp with 1 torr of argon as the carrier gas. Each line is measured from interferograms taken with a Fabry–Perot interferometer having 20-, 40-, and 50-mm spacers, and the results are averaged after making the correction for dispersion of optical path. The combination principle is used as a test of the accuracy of the measurements. The average wavelength error is about one part in 3 to 6×10⁷ and the average root-mean-square deviation is 1.6×10⁻⁴ Å between the results for the different spacers. Our results are compared with those of different investigators and indicate a relative shift of +4×10⁻⁴ Å when the electrodeless discharge tube is compared with the hollow-cathode lamp. The origin of this shift is discussed and attributed partly to differences in the standards used to calibrate the interferometer and partly to differences in the light sources.

© 1969 Optical Society of America

Thorium Lamps and Interferometrically Measured Thorium Wavelengths

Francisco P. J. Valero
J. Opt. Soc. Am. 58(4) 484-489 (1968)

Interferometric Wavelengths of Thorium Lines between 9050 and 2566 Å

T. A. Littlefield and Anne Wood
J. Opt. Soc. Am. 55(11) 1509-1516 (1965)

Interferometric Wavelengths of Thorium Lines between 2650 A and 3400 A*

A. Davison, A. Giacchetti, and R. W. Stanley
J. Opt. Soc. Am. 52(4) 447-451 (1962)

Analysis of Interferometrically Measured Wavelengths and Their Application as Secondary Standards of Length

Francisco P. J. Valero
J. Opt. Soc. Am. 60(12) 1675-1680 (1970)

Proposed Secondary-Standard Wavelengths in the Spectrum of Thorium*

A. Giacchetti, R. W. Stanley, and R. Zalubas
J. Opt. Soc. Am. 60(4) 474-489 (1970)