Paper 6.3: N. Bloembergen, “The influence of electron plasma formation on superbroadening in light filaments,” Optics Comm. 8, 285–288, 1973.

During the spring of 1973, I spent a sabbatical leave in my native country, the Netherlands. I was the Lorentz guest professor at the University of Leiden, where I presented a special course on nonlinear optics. My host at the Lorentz institute for Theoretical Physics was Professor Peter Mazur. Professor C.J. Gorter was still directing the Kamerlingh Onnes Laboratory, while Professor Johan van der Waals had an active research group at the new Huyghens laboratory. I also interacted with many other colleagues whom I had known since my stay at Leiden as a research fellow in 1947 and 1948.

Active research in nonlinear optics was carried out at the Philips Research Laboratories in Waalre, near Eindhoven by a group which included B. Bolger, D. Polder, C.J.E. Schuurmans, Q.H.F. Vrehen and J.P. Woerdman and several others. At the invitation of G.W. Rathenau, who was one of the directors of the Philips lab, I served as a consultant. During our discussions of the recent literature, the problem of frequency broadening by self-phase modulation came up. It occurred to me that the creation of a plasma following electric breakdown by short intense light pulses would cause rapid changes in the index of refraction. This note was written during my employ of four months at the Philips Laboratories in Waalre.