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Resonant dip of two-photon ionisation and stimulated emission in laser-pumped magnesium vapour

An anomalous resonant dip of two-photon ionisation with 3s3p 1P as an intermediate state and a stimulated emission by the 3s4s 3S-3s3p 3P transition, at 518.37 nm following the pulsed laser excitation near the 3s2 1S-3s3p 1P resonance at 285.21 nm in magnesium vapour are observed and studied. The mechanism of the ionisation dip is attributed to formation and predissociation of the A 1 Sigma +u Mg2 dimer, which transfer the population from the laser-pumped 3s3p 1P level to 3s3p 3P levels. Re-excitation of the produced 3s3p 3P atoms and the subsequent radiative processes are presumed to explain the generation of stimulated emission. A theoretical model is employed to interpret the experimental phenomena.