Tribute to Professor Rodney Loudon, 1934-2022

Professor Rodney Loudon was a world-renowned physicist best known for his work on light and quantum optics. He helped found the Physics Department at the University of Essex and received numerous international awards for his outstanding work. Here Professor David Tilley remembers his friend and colleague.

Rodney was born in 1934 in Prestwich, Lancashire, and passed away on Christmas Day 2022 in Ipswich Hospital. After school in Bury he gained admission to Brasenose College, Oxford where he graduated with Double First Class Honours in Physics in 1956. After his first degree he continued with research at the university physics laboratory, the Clarendon Laboratory, obtaining his PhD in 1959. His PhD supervisor was a young lecturer called Roger Elliott, who later attained considerable fame in posts including President of the Royal Society and Chairman of the Oxford University Press.

When Rodney started his PhD the laser had just been invented. The intense, monochromatic beam opened the door for the experimental study of the weak process of inelastic scattering of light. Here, inelastic means a slight frequency shift on scattering. With Roger’s guidance, Rodney found all of the scattering processes that would occur, and indeed those that would not occur, in crystals of various symmetry. A detailed account of these and later results is given in Rodney’s famous book with Bill Hayes, Light Scattering by Crystals (Oxford University Press, 1978). The results were of lasting value, and indeed the book is still on research workers’ desks today.

After Oxford Rodney took up a postdoctoral position for a year at Berkeley, University of California. This was a happy time, not least because he met and married his wife of 62 years, Mary. Having completed his postdoctoral time, Rodney returned to this country in 1960 to take up a post at the Royal Radar Establishment (RRE) in Great Malvern. This was the era of the big industrial and Government research laboratories, and Rodney’s work was of sufficient applied interest that he often collaborated with colleagues in research laboratories.

Rodney left RRE in 1965 to work for a year at the highly prestigious Bell Telephone Laboratories, New Jersey. He was then recruited in 1966 to set up the theoretical side of the Physics Department at the new University of Essex. He started as a Reader, but after a year, in 1967, he was promoted to Professor, a post he held for the rest of his life. He continued to pursue his interest in light scattering in crystals, notably extending his work to magnetic crystals during a sabbatical period in 1970 at Bell Laboratories in New Jersey. He continued to develop his interest in the interplay between the wave and particle properties of light, and made the results accessible in successive editions of his book Quantum Theory of Light (Oxford University Press, 1973, 1982 and 2000).

Rodney and Mary created a very full and satisfying life for themselves in the village of East Bergholt, where they were able to buy an excellent plot of land and build a lovely house to their own specification. Here, over the years, Mary designed and developed a beautiful garden. By the time they moved into their house, they had two children, Ann and Peter, whom they brought up there.

Rodney’s illustrious achievements in research could easily be allowed to obscure his distinction as a university teacher, but that would not be right because he was an excellent lecturer and teacher at all levels. I remember on more than one occasion warning undergraduates that just because Rodney made something look easy in lectures they might not themselves find it that easy. Allocating lecture courses as Chairman is rather like placing the field in an old-fashioned cricket team: the more portly fielders have to be placed somewhere rather remote where the ball might hit them and thus avert a boundary. Rodney, by contrast, was the sprightliest member of the team and was always entrusted with the most important courses.

Rodney’s human qualities shone through in the compassionate and thoughtful way in which he always treated his friends and colleagues. I shall never forget the words of comfort he spoke to me when my father dies unexpectedly in 1968, which in fact was not long after Rodney’s own father had died.

By the mid-1970s the focus in condensed-matter physics was increasingly on confined volumes, particularly films and other systems with surfaces and interfaces, and Rodney extended his previous research work in both light scattering and quantum optics to include surfaces explicitly, something that had not been done before and was of considerable importance.

Rodney’s increasing eminence led to the award of a number of prestigious prizes, notably the Institute of Physics Young medal (named after the early 19th century polymath Thomas Young, often described as the last man to know all there was to know) in 1987, the Max Born Award of the Optical Society of America in 1992 and the Humboldt Research Prize of the German Physical Society in 1999. In recognition of his achievements he was elected Fellow of the Royal Society in 1987, and in fact he was one of three founding members of the Physics Department to be thus recognised.

Although Rodney’s heart was in physics and physics research, he was sought after for various committees concerned with the organisation of physics, notably as a member of the Institute of Physics Council. His most important work of this kind was with the Opto-Electronics Group of Rank Prize Committee, on which he served for a lengthy period from 1988 to 2011. The Rank Prize is awarded annually at a week-long meeting in Grasmere, Cumberland, for an outstanding piece of research. For many years the Rank meeting has been right at the forefront of condensed-matter research, and it was the guidance of committee members like Rodney that ensured that it kept this position.

Away from physics, Rodney enjoyed woodwork and singing in choirs, both offering a break from the cerebral nature of his professional work. Visitors to the house in East Bergholt could not fail to be impressed by the beautiful harpsichord, the splendid dining table and the remarkable Library Steps that Rodney so carefully and exactly constructed. For many years he sang as a bass with the University of Essex choir and the East Bergholt Church choir, indeed until advancing years and frailty made him retire. Rodney always enjoyed classical music concerts and as a ‘cultured gentleman’ he was knowledgeable on a range of topics, including literature, painting, good food and wine and particularly church architecture.

Rodney’s funeral will be held at East Bergholt parish church on Wednesday 8 February. Many friends and former colleagues will gather to say farewell to one of the kindest and gentlest people we have known.

If you would like to submit a tribute to Professor Loudon please email comms@essex.ac.uk and it will be added below this article.

Tributes

I first met Rodney Louden in the wild days of the early 1970’s as a young undergraduate at Essex University. Rodney taught me Quantum Mechanics, something I had never encountered before, and I must say that I enjoyed it. Later, in my final year, I was doing a project supervised by Professor Alan Gibson that concerned the interaction of laser light with semiconductors in high electric fields. During the evolution of my experimental work, it became evident that something was quite different to what had been expected and we needed to resort to some significant mathematics in order to understand it.

Put simply, not being that mathematical at this stage, I became very hopelessly stuck. I recall later, one long afternoon in the lab, Alan Gibson came to see how I was getting on, I explained the problem, best I could, only having a rudimentary understanding of the theory. In his finest way, Alan tried to "think it through with me” accompanied with much fiddling with his pipe and matches. After 10 minutes like this, Alan swung around rapidly to walk away, a gesture that those who know him will remember well. After about four steps he turned and said “ask Rodney” and then walked away. So, I went to Rodney’s office and was invited inside with much consideration. Rodney asked me to work through the mathematics, and I struggled painfully through a few steps. The problem required rather heavy tensor mathematics, and Rodney patiently watched my try to fight this beast the best I could.

The purpose of relating this memory is in the way that Rodney dealt with it. All those who knew Rodney know instinctively that he was very, very intelligent. This was accompanied with a rare sense of elegance and calm. He took a scrap of paper and started to try to solve, quickly reaching my impasse. After a few tries he found an unusual and unique operator approach and then the answers became much clearer. In the 10-15 minutes that this took, he watched me carefully, as I must have looked rather uncomfortable and well out of my depth. After slowly explaining his approach, he did something remarkable. He screwed up the paper and threw it towards the waste paper bin. I did what any student might do in such circumstances, thanked him, went immediately back to the lab and copied down as much as I could remember, in my lab book. And in the end it all turned out all right. The ease, grace and care of his approach was distinct and notable. The solution was left to me.

A few years after graduating, I returned to Essex to undertake an MSc in photonics and electronics, running into Rodney one evening whilst I was working in the Long Laser Lab, he greeted me with “you came back then!”. Later, I worked at Bell labs, and have spent much of my working life in The Bay Area and until today a substantial part of my work has been Quantum Mechanics and Photonics. Rodney was a very considerate and kind gentleman, who had the distinct advantage over most of us, in his exceptional intelligence. For all of his students and there must be many thousands, he was quietly inspiring, not only in his technical ability, which was outstanding, but for his special care and calmness. His “way” was to carry things through with such finesse and elegance. These are great memories, and I feel many others will share similar ones.
Steve Moffatt, Applied Materials Inc, Santa Clara, California

With great sadness I read that my teacher and friend Professor Rodney Loudon passed away on 25 December 2022. During my time as a PhD student at Essex I remember him as an extraordinary person, always kind and ready to help in everything, both academic and personal matters, in addition he also had a great sense of humour. I took with him a course based on his book "The Quantum Theory of Light", this is one of the most cherished memories I have of my time in Essex. I will never forget when during the first lecture he said: "I recommend my book not because it is very good, but because since it is the one I wrote it is the one I understand the best". Everybody laughed! And, I may add that his book is one of the finest and very best books written on the subject of quantum optics. At that time I was also a member of Essex Choir where I had to opportunity of sharing this passion with Professor Loudon. The truth is that I have great memories from my time at Essex Physics Department. I also have a great deal of gratitude to many friendly and kind people such as Professor Rodney Loudon.
Prof. Dr. Vicente Aboites, FInstP

Like Tony Khater, I was one of the first intake of students at the new Essex University in 1964 and was also fortunate to gain a Poulter studentship (in Physics and Archaeology). However, this first required passing the MSc in Quantum Electronics in 1967-68. As an experimental Physicist, I was both enthralled by, but struggled with Quantum Physics. Despite this, Prof. Loudon’s lectures were both a model of clarity and enjoyable. I still vividly remember my amazement at the lecture in which he theoretically derived the charge (or was it the mass?) of the electron to an unbelievable number of significant figures. Leaving the lecture, I felt that I had followed the maths and reasoning from start to finish. As David Tilley has commented, I did not find it that easy on looking over my lecture notes later! I am grateful to Prof. Loudon for being one of those outstanding lecturers who inspired me to pursue a career in Physics.
Dr Chris Mullins, Retired Reader in Soil Physics, Aberdeen University

As an undergraduate and then PhD student in the early days of the Essex Physics Department, I got to now Rodney well - both as a lecturer and as a researcher. His lecturing style was outstanding, bringing clarity to difficult subjects and always judging the pace of introducing new topics and explanations to perfection. Although we did not work directly together, my research on optical properties of semiconductors, under the direction of Prof Alan Gibson, brought me in contact with Rodney on a regular basis. I always recall - both as an undergraduate and subsequently, his extraordinarily modest and respectful nature. When answering a question, he had the knack of implying that you were the expert on the topic and that this was an opportunity for him to learn something as much as for you. After I left the Department, Rodney became interested in a key aspect of the research area upon which my PhD was based - the photon drag effect. In particular, the question 'what really is the momentum of a photon in a dielectric medium?'. This was a topic - which I must admit I treated very naively in my own thesis(!) - that had was proving controversial, with radically different theoretical conclusions in the published literature. Rodney's clarity and insight resolved the debate in his usual elegant style. I cannot finish without mentioning that Rodney was also excellent company socially - spending time with him and Mary was always a great pleasure. Many memorable occasions spring to mind, including visits to Easy Bergholt and a highly stimulating train journey from Edinburgh to London - all too many to list. A great man, sorely missed.
Andy Walker - Emeritus Professor, Heriot-Watt University

With great regret I was aware of the death of professor Roudney Loudon the well known scientist in quantum optic. He was a very nice and lovely human being and as one of his PhD student I never forget his great personality. I should say I learned too much from him in my life. God bless him
Heidar Khosravi

I had the privilege of being Rodney's last PhD student. I still record the little fear I had when starting my new adventure at the University of Essex early 1998 after my master's degree in Physics at the University of Rome La Sapienza. Rodney has been an incredible guide and support to me both at the beginning and throughout the whole three years of PhD studies. He taught me to write clearly and concisely in English, and always encouraged me with enthusiasm in my research. I enjoyed so much working with him. I am proud to have published scientific articles with him, and I am thankful to him for having taught me the theory of Quantum Optics, with clear and elegant equations and explanations. I have very nice memories of my three years in Essex. I also remember the lunches at Rodney and Mary's house who always welcomed me with affection. Certainly having met Rodney during my studies was an incredible fortune, and I owe much to him of the scientist that I have now become.
Ottavia Jedrkiewicz, CNR (Como, Italy)

We had the honour and privilege to work with Rodney at Essex for some years. We were amongst the last people at Essex to collaborate on research with Rodney, but the long list of his collaborators and former students extends around the globe, including the world’s top universities. In addition to being a very distinguished scientist, he was one of the friendliest and most helpful people we have known, very kind and generous with his time. We were always impressed by the combination of Rodney’s towering standing as a scientist and his characteristic modesty (the latter was perfected almost to the level of a martial art). In particular, we recall working with Rodney on an EPSRC research project “Optically-injected multi-section lasers for chaotic encryption systems” (2006-2010). Rodney’s technical input was (of course) outstanding. His natural deep scientific insight and intuition always worked as a guide to keep a research focus on the most essential physics, which is the greatest golden gift of any real scientist. In mentoring, Rodney always gave his encouragement and guidance to the research student and post-doc on the project, whilst at the same time appreciating their contributions, all of which ensured the project’s success. He will be sadly missed, but his legacy will live on in many ways.
Professor Emeritus Mike Adams and Dr Nick Zakhleniuk 

I did not come to the Physics Department at the University of Essex until January, 1991, and that is when I met Rodney Loudon for the first time, but I knew of his work long before that. I worked throughout most of my career in the field of solid state spectroscopy, and in the 1960s Rodney published a seminal analysis of infrared and Raman selection rules in simple ionic and semiconductor crystals using the mathematical technique of group theory. This was an important paper for anyone trying to interpret their infrared and Raman spectra of these materials. Rodney published this work before he turned his attention to quantum optics, for which he is best known. After I came to Essex my wife Anne and I had the pleasure of attending many concerts in which Rodney sang in the choir. I remember that when they could no longer drive we also took Rodney and his wife Mary occasionally to concerts at St Mary's church in Stoke by Nayland and to the autumn and winter series of operas at the Regent Theatre in Ipswich by the Moldova Opera Company and ballets by the Russian National Ballet from Novosibirsk. Rodney was clearly brilliant in his chosen field, but he was also a very warm and supportive person. It was a privilege to know him and I consider it an honour to have counted him amongst my friends.
Terry Parker, Essex

How to sum up an association of nearly forty years, my entire academic career? Perhaps I should start at the beginning. I first got to know Rodney from his classic text “The Quantum Theory of Light”, all elegance and lucidity, and perfectly formed for the beginner, such as I. I soon discovered that these attributes were those of the man himself. A seminar by Rodney was all clarity and so easy to follow that I would wonder why I had not seen what he had seen, so ‘obvious’, at least in hindsight, were the steps, so coherent was the line of reasoning. Early in my career Rodney was a mentor and looking back, I can see aspects of my approach to science remaining today that had their origin in Rodney’s example. Rodney became my valued collaborator and friend. Working with him was always enlightening and a pleasure in equal measure. That elegance and clarity, so apparent in Rodney’s book, were there in all his science, as were the charm, good humour, generosity of spirit and gentleness of the man himself. He was such a lovely man.
Stephen Barnett, Glasgow

I began as a student at Essex under Rodney’s supervision in the late 1980s. Although I was a little in awe, from the start he made me feel welcome as a researcher. He was always patient with my naive questions and sometimes foolish answers. In science terms the most important thing that he taught me is that the simple way of doing things is nearly always the best. I know that he imprinted a little of his brain into my way of working. I sometimes catch myself passing on to my students gems that I first learned in his office. After my PhD he became a collaborator for several years and he was always a friend. He was a gentle man and a gentleman – funny, kind, brilliant in the most understated way.
John Jeffers, Strathclyde

I can think of no colleague who earned more respect than Rodney. He generously gave his full considered attention to every matter, the same attention that characterised his scientific work. His two first books, on the Quantum Theory of Light, and on Scattering of Light by Crystals, were outstanding for their rigour, and remained classics long after they were first written. As someone myself who was also involved in the field of light scattering, I never ceased to be amazed how comprehensively Rodney had dealt with the theoretical basis of the topics.

As is well known, Rodney did get involved in an dispute with Karl Popper over the so-called Copenhagen interpretation of quantum mechanics. I recall that Rodney was deeply embarrassed how someone as eminent as Popper could fail to calculate properly the implications of what he was discussing. For Rodney, I felt that this embarrassment was perhaps even more important than the rights and wrongs of the discussion.

I was also often involved with Rodney in singing. It was typical of Rodney that he became Treasurer of the University Choir in its early days, giving great support when he had many other demands on his time.
Stephen Smith, Essex

I met Rodney Loudon at Essex University in 1967 for the first time, as a second year undergraduate student in his class, and later developed my research activities under his supervision for a Ph.D. in theoretical physics, supported by the Poulter Scholarship which Essex University awarded me. I did a M.Sc. with one of his colleagues during the academic year 1968-69, and then changed to work with him for a Ph.D. But Rodney forgot to tell me before leaving to the USA that year, the proposed theme of my thesis, and I had to fly to Bell Labs in New York in the summer of 1969 to discuss this with him. Afterwards, I left New York to go to Montreal in the north, and met him again, accidently, in a Harvard University restaurant at lunchtime, which triggered our laughter. Back at Essex in the fall I started my research work, with him in his office down the corridor.
Out of this period, a notable friendship grew between us despite the differential in age and status, and also between our families and wives later in life. I came back to Essex as a visiting Lecturer in 1977-79, and worked with him and with other colleagues. Our friendship lasted more than fifty years, regardless of where I was as a university professor and researcher, in England, Brazil, Lebanon, and since 1984 in France, through letters, emails, phone calls, and occasional visits. Aside his exceptional scientific achievements which made him a Fellow of the Royal Society, Rodney was a very modest and descent man whom you can trust, and with whom you can enjoy dinner joyfully with a glass of wine. Rodney Loudon was a moral as well as a scientific reference, and a caring humane colleague.
Tony Khater Distinguished University Professor (CE), University du Maine, France