Laser Emission in Ionized Mercury: Isotope Shift, Linewidth, and Precise Wavelength*

The 6150-Å laser transition in Hg ii generated in a pulsed hollow cathode discharge, has been studied under high resolution. The line shows structure corresponding to the expected shifts from the even isotopes, with a spacing of approximately 26.5 mK (800 Mc/sec) between adjacent components, in rough agreement with earlier results. The fullwidth at half-maximum of each component has been measured as 500 Mc/sec. The wavelength has been compared to that of thorium secondary wavelength standards and it has been determined that the vacuum wavelength of the 202Hg component is 6151.1650 Å. The possibility of the mercury hollow cathode laser as a laboratory wavelength standard is pointed out.