Lineshapes and optical selectivity in high-resolution double-resonance ionization mass spectrometry

Lineshapes expected in high-resolution double-resonance ionization spectroscopy are calculated using the density matrix formalism, integrated over experimentally realistic conditions including atomic velocity and angular distributions as well as laser intensity profiles. The results of these calculations are compared with experimental measurements on the system 4s(2) S-1(0) --> 4s4p P-1(1) --> 4s4d D-1(1) --> ion for calcium. The measurements of lineshape, with a dynamic range of > 10(6), reveal and confirm subtle effects predicted by theory. These include the shape, position and intensity of the laser-induced structure in the spectra and the simultaneous presence of coherent and incoherent excitation processes. The calculations are able to accurately predict isotopic selectivities achieved in experimental resonance ionization measurements and are used to evaluate these values for the detection of minor calcium isotopes, including the radionuclide Ca-41. (C) 1999 Elsevier Science B.V. All rights reserved.