Controlling isotopic effects in the resonance ionisation mass spectrometry of krypton

We have investigated and characterised possible sources of variation in measured isotope ratios in the resonance ionisation mass spectrometry of krypton using resonant transitions at 116.48 and 558.04 nm and ionisation at 1064 nm. Variation arises when the spectral width of the hyperfine structure of the odd isotopes is comparable to the laser bandwidth and from the alignment of the first excited state, which depends on the relative polarisations of the laser pulses exciting the resonant transitions.