Abstract

Previous investigations have shown that atomic vapours produced by cathodic sputtering in a low pressure rare gas discharge provide a suitable source of ground state atoms, metastable atoms and singly-charged ions for conducting high resolution, Doppler-free experiments in a wide range of atomic systems. In this work we report the application of laser saturation spectroscopy in a sputtered vapour to the measurement of isotope shifts and hyperfine structures in near ultra-violet transitions of Pb I. The transitions studied are 405.8 nm $\left(6{\text{p}}^{\text{2}}{}^3{\text{P}}_{\text{2}}-6\text{p7s}{}^3{\text{P}}_1^0\right)$, 368.3 nm $\left(6{\text{p}}^{\text{2}}{}^3{\text{P}}_{\text{1}}-6\text{p7s}{}^3{\text{P}}_0^0\right)$ and 364.0 nm $\left(6{\text{p}}^{\text{2}}{}^3{\text{P}}_{\text{1}}-6\text{p7s}{}^3{\text{P}}_1^0\right)$ for which the metastable lower levels (³P₁7891 cm^–1, ³P₂10650 cm^–1) are readily populated in a lead hollow cathode discharge at a low pressure of argon. The spectra were obtained using the frequency doubled output from a narrow band cw titanium sapphire laser with an intracavity LiIO₃crystal. In order to minimise the effects of Doppler-broadened background pedestals which can result from velocity changing collisions with rare gas atoms, the pump laser beam is chopped at high frequency (300 kHz) and the discharge operated at low rare gas pressures (0.5 Torr). In the case of the 368.3 nm $6^3{\text{P}}_{\text{1}}-6^3{\text{P}}_0^0$ transition, for which the branching ratio is unity and the upper level lifetime is short, pedestal-free spectra exhibiting Lorentzian lineshapes can be observed over a relatively wide range of chopping frequencies and rare-gas pressures (see Figure 1). This result is in accord with the results of rate equation calculations of saturated absorption spectra in a closed two-level system.^[1]

© 1992 IQEC