1. P.M.W. French and J.R. Taylor, Laser Focus Feb. 1989 gives a recent review, and P. Georges, F. Salin and A. Brun, Opt. Lett. 1A, 785 (1989).
2. W.H. Knox, Postdeadline paper PD31, CLEO 1989, Baltimore, MD
3. W.H. Knox, G.E. Doran, B. Tell, K.W. Goossen, G. Hasnain, J. Cunningham and D.S. Chemla, IEEE JQE 2. 5, 2586 (1989).