My memories to Stanisław Kielich

Late in the fifties of the last century, as a young student of the Physics Department of Poznan University, I became fascinated with Professor Stanislaw Kielich’s lectures on the nonlinear optical phenomena. At that time, his first theoretical papers on the optical nonlinearity of matter were published. These publications were a consequence of his earliest works on the dielectric saturation of liquids. Just after my graduation from Poznan University, I applied for a post at the Institute of Physics of the Polish Academy of Sciences in Poznan, closely co-operating with the Division of the Experimental Physics at Poznan University. This was why our laboratory took up studies in the field of nonlinear optics. In those days (the beginning of the sixties), the first lasers were constructed at the best world-wide laboratories. Our knowledge on the lasers was residual but our enthusiasm was enormous. This enthusiasm let us construct, at the end of 1963, the first Polish ruby laser which emitted the coherent beam of the red light and so our laboratory was ready to undertake studies on nonlinear optical effects in matter. One of our aims was experimental confirmation of the Kielich’s theory. My PhD thesis, defended in 1969, was devoted to the simplest nonlinear optical effect – second harmonic generation (SHG). I had proposed the generation of the light’s harmonics not in single crystals but in powdered samples. My method of the investigations of SHG was fully original and relatively simple. It was published in Acta Physica Polonica – scientific journal of limited reach. Stanislaw Kielich was one of the scientists who appreciated this method and cited my paper on frequent occasions. I made friends with my former professor and the oldest colleague in 1971, in Bordeaux (France) where I continued with my postdoctoral studies. At that time, Stanislaw Kielich – Staszek for his friends – was Associate Professor at the University of Bordeaux in Talance. Though we were working in different laboratories, our relations were very close and friendly. Naturally I took part in his lectures devoted to recent developments in the theory of nonlinear optical effects; his lectures took place at the biggest conference room of the Centre de Recherches Paul Pascal, which was always filled to capacity. It is necessary to say that the participants of Staszek’s lectures were bombarded with enormous, very long and complicated formulas written on a blackboard just from memory. What an extreme memory it was! In the midst of the audience many professors, younger scientists and PhD students. Novel, yet unpublished concepts, and the original form of Stanislaw’s lectures appealed hugely to the audience. Phenomena and new effects anticipated by theoretical investigations of Staszek were tested by experimenters of the