A single-transverse-mode $Q$-switched Nd-glass laser, which can operate over a variable number of longitudinal modes, has been used to investigate the influence of the temporal nature of the laser pulse on the multiphoton ionization probability of xenon atoms. For a seven-mode laser pulse, the number of ions formed is increased by several orders of magnitude over that produced by a single-longitudinal-mode laser pulse.

• Received 29 October 1973

DOI:https://doi.org/10.1103/PhysRevLett.32.265