A photon echo from the allowed 3D-3P transition in Na vapor is spontaneously emitted after a single-pulse one-photon excitation of the 3P state is followed by a single-pulse two-photon excitation of the 3D state. The collisional relaxation cross section of the excited 3D-3P superposition state of Na in Ar is measured.
© 1986 Optical Society of America
T. J. Chen, D. DeBeer, and S. R. Hartmann, "Observation and relaxation of the two-photon-excited trilevel echo in sodium vapor," J. Opt. Soc. Am. B 3, 493-496 (1986)