I would like to recall my experiences when I joined George Series when on study leave from the University of Otago in 1959. Like George, we had decided, some years previously, to pursue the line of research opened up by the double-resonance experiment of Brossel and Bitter. Up to that time both groups had been applying the new technique to traditional spectroscopic problems, those of measuring the fine structure, hyperhe structure, g-factors and nuclear moments. But here, in Oxford, was something new and exciting - experiments that studied the nature of light itself, questioning some long-held views. George had come to the view that, in a double-resonance experiment, one could demonstrate the inner coherence that could exist between superposition states of an atom. He, and his students Wilf Fox and Mike Taylor, had already obtained promising evidence; but he needed more definite results if he was going to allay the doubts and suspicions of some others in the Clarendon. At the time, people generally thought that light, being a superposition of radiations from many atoms with no obvious phase relation to each other, was an incoherent wave phenomenon. One could observe small scale coherence (for example, in the Young interference experiment) but it would be largely concealed by the incoherent nature of the radiation from many atoms in a source. In the experiments that had been performed the coherence was introduced between a pair of
excited states (Zeeman sub-states) by the application of an oscillating magnetic field - was it not likely, according to the doubters, that the modulation observed in the fluorescence was due to "pick-up" in the amplifiers from the source of oscillations? George had to prove that this was not the cause. I well remember him saying at the time "I have a hunch that I am correct". That typified his approach to physics. The work of 1959 demonstrated beyond all doubt that substantial coherence, manifested as strong beats in the intensity of the light, could be obtained. The experiments demonstrated this to be the case. We also worked out the theory of the effect.
In the theoretical explanation of the experiments, both George and I were impressed by the success of a semi-classical approach - i.e. by treating the atom as a quantum-mechanical structure and the light as an electromagnetic wave. This viewpoint dominated much of George's work in later times. As he stated in the Memoirs, "I came to the conclusion that the key problem in the interaction of electromagnetic fields and atoms was the nature of spontaneous emission. I accept the quantum field theory as giving an adequate mathematical explanation, but this seems to me to be deficient as a physical explanation". I think it is fair to say that George was always seeking a deeper physical meaning than was provided by a mere mathematical description. This philosophy certainly rubbed off on people who worked with him.
That year, 1959, was also the year when coherence in light beams was being studied in other laboratories across the Atlantic. It was the year the laser was born. There was no doubt then about coherence in light.
I would also like to mention the great regard that George had for S. Pancharatnam who came to work at the Clarendon in 1964. George and Panch spent many hours in discussions. Although they never published anything jointly, George recalled that, if he was doubtful about some point of physics, he would refer to Panch. As he wrote in a moving review for the Pancharatnam Memorial Issue of Current Science (Vol. 67, August 1994), "Panch was not easily moved from the conventional view [of the nature of the interactions of light and atoms]. I was more impetuous; Panch was generally right". George edited the collected works of Pancharatnam; he went to India as a Raman Visiting Professor in 1982 and was made an Honorary Fellow of the Indian Academy of Sciences in 1984.
At Reading [from 1968 to 1982], he increasingly turned to spectroscopy with tuneable lasers, generally with the emphasis on understanding the underlying physics rather than accumulating data. He had a highly original mind, which showed both in his choice of research topics and in his method of approach. He did not follow fashion; his instinct for an interesting problem was at odds with the modem policy of direct funding and the identification of "growth areas". His applications for research grants were often unsuccessful, despite his high international standing and integrity. He was never interested in building up a large research team, and had comparatively few research students, but his enthusiasm and commitment to the quality of his science attracted a succession of overseas visitors to his laboratory. Following my own year at the Clarendon, and some subsequent visits both to Oxford and to Reading, there was a continuing strong association between the Clarendon and Otago Physics that continues until today. George Series was the William Evans Visiting Professor to Otago University in 1972.
He never lost his interest in the fundamentals of physics inspired by his first researches into the structure of the hydrogen atom; he wrote on the Rydberg constant, the physics of spontaneous emission, and on the fine-structure constant α = e2/hc. He donated a garden seat to St Edmund Hall (Oxford), of which he was a Fellow. On it he placed a plaque* in recognition of the ubiquitous nature of this constant; it almost had magical significance for him.
He served physics in many ways outside research. He was for a number of years the Editor of the European Journal of Physics and was also Editor of the Journal of Physics B: Atomic and Molecular Physics, He was also on the Editorial Board of a number of journals. He was elected to Fellowship of a number of physics societies.
The Editorial Board of these Memorial Essays dedicate them to George's memory, and to his wife Annette and his family.
