Obituary:Professor George Series

George William Series, physicist: born 22 February 1920; Lecturer, St Edmund Hall, Oxford 1953, Fellow 1954-69 (Emeritus); Professor of Physics, Reading University 1968-82 (Emeritus); FRS 1971; William Evans Visiting Professor, University of Otag o 1972;married 1948 Annette Pepper (three sons, one daughter); died Oxford 2 January 1994.

Freshmen arriving at university to read physics often have a sense of wonder and excitement at the prospect of learning the secrets of nature. George Series, one of the outstanding atomic spectroscopists of his generation, maintained this feeling unabated throughout his life.

His teaching and lecturing were at once fascinating and disturbing, being carried out with a missionary zeal so intense as to make the less committed feel distinctly uncomfortable. As a scientist, he will be remembered as much for his enthusiasm and his delight in the subject as for his contributions, substantial though these were. As a man, he will be remembered for his kindness, courtesy, and outstanding conscientiousness and integrity. He gave "family" as his recreation in Who's Who, and indeed family and physics were the two great passions of his life.

Born in 1920, he won scholarships first to Reading School then in 1938 to St John's College, Oxford, where his studies were interrupted by the Second World War. He served in Egypt, Italy and Yugoslavia from 1940 to 1946 with the Friends' Ambulance Unit, then returned to Oxford to take a First in 1947. He was based in Oxford until 1968, becoming a University Lecturer in 1951 and a Fellow of St Edmund Hall in 1954. He then took a Chair at Reading University, where he remained until his retirement in 1982.

His early research was on optical spectroscopy of simple atoms, notably hydrogen. Hydrogen, as a testing ground for theory and a source of fundamental constants, fascinated Series, who became a world authority on the subject. In those pre-laser days, he pushed classical interferometry to its limit in studying optically the recently discovered Lamb shift, a crucial piece of evidence in the development of quantum electrodynamics (QED), the quantum theory of electromagnetic interactions. Later, he took part in a measurement of the Rydberg constant, an important combination of fundamental constants. He wrote a book, The Spectrum of Atomic Hydrogen, in 1957, and edited a second, The Spectrum of Atomic Hydrogen: Advances (1988).

In the Fifties and Sixties, however, he achieved international recognition in a different field. Alfred Kastler's group in Paris had found a new way of applying radio-frequency techniques to atoms, combining them with optical excitation. This gave an enormous gain in resolution by comparison with conventional optical spectroscopy. Series saw at once the potential of the approach and exploited it, extending the method and contributing to the theory, but he realised also that coherent excitation of different states could produce interference effects (now known as quantum beats) if one examined the fluorescent light as a function of time. To quote one of his papers: "We looked, and it was so." This general principle of time-dependence was exploited by Series and his colleagues in a series of beautiful and innovative experiments, backed up by theory, and became an established spectroscopic tool.

In the final phase of his experimental research, Series turned to high-resolution techniques based on the newly developed tunable dye laser, drawing on this expertise in quantum beats and line-narrowing.

He was interested not so much in solutions to problems as in beauty and simplicity, and so found much that others missed. He acknowledged the success of QED, but found the semi-classical theory, in which the atom is treated as a quantum mechanical systembut radiation is not, to be much more aesthetically pleasing. He cherished the ambition, never, alas, realised, to explain without recourse to QED how an atom comes to radiate spontaneously. However, his reflections on this process produced many insights: he pointed out, for example, that the radiation width of a spectral line, which had always been assumed to set a resolution limit, can be reduced by selecting atoms which take longer to decay.

George Series had a number of gifted students, but he also attracted distinguished visitors from all over the world. He had a particular affinity with the group of J.N. Dodd at the University of Otago, where he was William Evans Visiting Professor in 1972. His regard for the work of S. Pancharatnam gave him a tie with the Indian Academy of Sciences, which awarded him a Raman Visiting Professorship in 1982, made him an Honorary Fellow in 1984, and published in the same year a selection of his papers, Laser Spectroscopy and Other Topics.

An effective speaker, Series was much in demand for conferences. The energy, commitment and attention to detail he showed in research were also evident in his other activities. The tradition for excellence of the Optics Practical Teaching Course in Oxford, which he developed with Heinrich Kuhn, has lasted until the present day. He edited two journals and was a member of several editorial boards. He chaired and served on Research Council and Institute of Physics committees. He was a Fellow of the Former Physical Society, and a founder member of the European Group for Atomic Spectroscopy. He was elected to the Royal Society in 1971, and received the Meggers Award and Medal of the Optical Society of America in 1982.

Derek Stacey