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 5p states of krypton and the 6p', 7p, 8p, and 4f states of xenon. Multiphoton ionization spectra are also obtained and compared with the photon-detected excitation spectra. In krypton coherent emissions from the 5p states to the 5s are observed, and for xenon many p{→}s, d{→}p, and f{→}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 p{→}s emissions are not understood at present. Interference effects due to coherent cancellation between competing excitation pathways may be occurring.