Number 75 (Story #1), April 10, 1992 by Phillip F. Schewe and Ben Stein A TWO-PHOTON OPTICAL LASER has been developed by Thomas Mossberg at the University of Oregon (Physical Review Letters, 27 Jan. 1992). In this laser system, a beam of barium atoms is pumped by a laser beam tuned to excite the atoms to special doublet states. A separate trigger laser beam, parallel to the main cavity and at right angles to both the barium beam and the pump beam, initiates a laser action in which the barium atoms emit not one but two photons simultaneously. A plot of the two-photon power intensity as a function of time shows a small, unexplainable oscillation. (Physics World, April 1992.)