A lineshape study of resonant multiphoton ionisation process: Effect of laser bandwidth on the power broadening

The spectral broadening of the two-photon resonant, three-photon ionisation is investigated in sodium. A simple model, involving Bloch-type equations, is found to compare favourably with the experimental results. The effect of power broadening combines with both the finite laser bandwidth and the lifetime broadening, making the selectivity of the ionisation process critically dependent on the laser monochromaticity. © 1995.