Oscillation spectra in He-Zn II and He-Cd II hollow cathode metal vapor lasers

This paper reports the measurement for the oscillation spectra in He-Zn II lasers at the 492.4 nm line and He-Cd II lasers at the 533.7 and 537.8 nm lines of the hollow cathode (HC) type with natural zinc or cadmium. The oscillation width of these lasers, which amounts to more than 2000 MHz, is unexpectedly broad in comparison with the theoretical gain profile; and the isotope shifts of the spectra which are caused by any two isotopes whose mass numbers differ by unity (
\DeltaM = 1
) can be estimated to be as much as 300-500 MHz to explain such a broadened oscillation width. The dominant reason for the large isotope shifts is not so much the mass effects as the volume effects. The behavior of the spectra at the axial mode competition is also measured. The extraordinary appearances of the mode competition can be attributed to the influence of the isotope shifts upon the oscillation spectra. Moreover, the axial mode separation at the beginning of the mode competition is nearly coincident with the decay rate of the upper laser level.