Two-photon resonant multiphoton ionization and stimulated emission in krypton and xenon.

Forward- and backward-directed, stimulated emissions have been observed following two-photon pumping of the 5{ital p} states of krypton and the 6{ital p}{prime}, 7{ital p}, 8{ital p}, and 4{ital f} states of xenon. Multiphoton ionization spectra are also obtained and compared with the photon-detected excitation spectra. In krypton coherent emissions from the 5{ital p} states to the 5{ital s} are observed, and for xenon many {ital p}{r arrow}{ital s}, {ital d}{r arrow}{ital p}, and {ital f}{r arrow}{ital d} cascade emissions are observed. By analogy to the well-studied alkali-metal and alkaline-earth examples, the emissions are assigned as amplified spontaneous emission. Several intensity anomalies in the xenon {ital p}{r arrow}{ital s} emissions are not understood at present. Interference effects due to coherent cancellation between competing excitation pathways may be occurring.