1. For a recent review, see, e.g., H. Walther, ed., Laser Spectroscopy of Atoms & Molecules, Springer-Verlag, Heidelberg, 1976.
2. T. W. Hansch and A. L. Schawlow, Opt. Comm.,13, 68 (1975).
3. S. L. Kaufman, Opt. Comm.17, 309 (1976).
4. Similar line narrowing was observed in molecular ions by W.H. Wing, G.A. Ruff, W.E. Lamb, Jr., and J. J. Spezeski, Phys. Rev. Letters36, 1488 (1976), using collisional detection.
5. G. Moruzzi, K.-R. Anton, S.L. Kaufman, W. Klempt, R. Neugart, E.-W. Otten, and B. Schinzler, contributed paper at Int. Conf. on Physics of Electronic and Atomic Collisions, Orsay, 1977.