It is quite clear that in those circum­ ALFRED KASTLER stances, one gets large population dif­ ferences between the Zeeman | m > J. Brossel, Paris sublevels of the excited state, which can (University of Paris VII be destroyed by many different proces­ ses including collisions and a radiofre­ quency field inducing transitions bet­ of Daure who had just retired. In 1941, G. ween the | m > substates. This opened Alfred Kastler, who died recently in the possibility — this is the so-called Bandol, southern France, was born in Bruhat called him to the Ecole Normale Supérieure in Paris (to take over the "double resonance" method 1) which Guebwiller, Alsace, in May 1902. was described in 1949 2) and demons­ As a young boy, he went to school in teaching duties of P. Auger who had left for the USA and Canada as a refugee) trated experimentally at M.l.T. the same Colmar, and followed a typical cursus of year — of extending the methods of German education (1914-1921). Until the where he was to stay until he retired in 1968. (A few years before his retire­ radiofrequency spectroscopy to the age of 19, he used the German language study of atomic excited states. The and spoke no French. In 1921, at the end ment, he resigned from Paris University to become a Directeur de Recherche at method does not require a high optical of the first world war, he became a stu­ resolution, even though an enormous dent at the Ecole Normale Supérieure in the Centre National de la Recherche Scientifique.) gain in precision is obtained because Paris and chose to become a physicist. one substitutes the natural line width to His teachers, there, were H. Abraham Between 1938 and 1951, Kastler wor­ ked on the Raman effect of mono-crys­ the Doppler width. A similar situation is and E. Bloch and they exerted a great obtained when atomic excitation is scientific influence on him until their tals and on the emission of the NaD line in the light of the night-sky. His PhD achieved with a directed beam of low death during the second world war. energy electrons (or ions, or neutrals). Bloch, in particular, introduced Kastler to work in 1936 on the polarization of the atomic physics, a field he never left. fluorescence of Hg vapour appears now Considering then the case of an atom Over five years (1926-1931), Kastler to have been a very important step in the with a paramagnetic ground state (with taught physics at the high school level in direction of what was to become "opti­ Zeeman substates | µ > ), Kastler descri­ Mulhouse, Colmar and Bordeaux, deve­ cal pumping". bed in 1950 the "optical pumping cycle" loping through this experience, a great Kastler knew in great detail Sommer- 3): submitted to an optical excitation talent for teaching. All his life, he remain­ feld's book Atombau und Spektrallinien with circularly right polarized light, the ed convinced that high quality teaching and he had been extremely interested in atomic system goes from | µ > to | m > was essential for young people hearing the Chapter in which the principle of where m = µ+1. Falling back to the for the first time of a new domain in angular momentum conservation is ap­ ground state through spontaneous science. plied to the interaction between the emission, it is then transferred from | m In October 1931, Kastler became an electromagnetic field and an atomic sys­ > to ground states with magnetic quan­ assistant to P. Daure at the University of tem. This had led Rubinowicz to explain tum numbers m—1, m, m + 1 (via  + ,  Bordeaux and in 1936 obtained his Doc­ the selection and polarization rules in the and  - polarizations), i.e. to states | µ >, torat ès sciences (Paris University), Zeeman effect. Kastler applied the idea | µ +1 > and | µ +2 > : on the average becoming soon after professor at the to calculate the polarization of the fluo­ then angular momentum increases, and University of Clermont-Ferrand. Two rescence following the excitation with a macroscopic polarization < Mz > ap­ years later (1938), he was appointed at polarized light of resonance radiation pears in the ground state : there is a con­ the University of Bordeaux to the chair and stepwise excitation. tinuous transfer of angular momentum from the ( + polarized) pumping beam to the atomic vapour. This polarization (or alignment in the case of a  pumping beam) can be destroyed by collisions, resonant RF fields, etc. Clearly, optical signals can be built on an auxiliary detecting beam to monitor a number of observables (longitudinal as above, or transverse (like < Mx >) as has been shown later on). Optical pumping, in the broad sense, has brought about a complete renewal of atomic physics and has been develo­ ped successfully over the last 30 years. The 1966 Nobel Prize in Physics was awarded to Kastler on this account and the gold medal of the Centre National de la Recherche Scientifique in 1966. These methods of optical pumping were developed at the Ecole Normale Supérieure in Paris and in many places the world over. They proved to be a very At the opening of the 1st EPS General Conference in Florence in 1969 with from left to right: powerful tool to study the interaction A. Kastler, V.K. Weisskopf, P.M.S. Blackett, G.H. Stafford (present EPS President), L. Jansen between the e.m. field (multiple quanta (then Secretary of EPS), L. Cohen (Treasurer) and the founding President G. Bernardini. transitions and associated non-lineari- 14 ties, light shifts, etc.) and many relaxa­ tion problems. Optical pumping magnetometers and atomic clocks have been developed : the Laboratoire de I'Horloge Atomique was set up in Paris by the Centre National de la Recherche Scientifique to investigate, at Kastler's request, how important this line of research might be. Kastler succeeded in creating a very favourable climate for basic research. He was very open minded, his knowledge of physics was very broad and deep. He put forward a great number of clever John Adams (second from left) in perhaps his finest hour as the SPS starts up. ideas. In the community of French physi­ cists, he stood as a person of great origi­ nality and, many times, as unconventio­ An Engineer Amongst Physicists nal. In a large measure, this was due to Europhysics News records with regret exploitation of the highly successful PS the fact that he had a deep and complete the death in March, at the age of 63, of and CERN's subsequent machines. In knowledge of French and German cultu­ another founder member of EPS — Sir European physics this was a new depar­ res. John Adams. Three times a Director- ture, the start of big centralised science He was deeply committed to interna­ General of CERN and Director of the on a continental scale for which CERN tional cooperation in the scientific and "300 GeV" proton synchrotron project still acts as the pole-star. political fields: his interest in the Interna­ (SPS), member of Council and the Whilst in England, Adams established tional Centre for Theoretical Physics in Scientific Policy Committee, as well as the thermonuclear fusion laboratory at Trieste and his participation in the many numerous international consultative Culham and after the euphoric period of activities of the EPS are two examples of committees, he had a major impact on the early 60s supervised its subsequent this involvement. He was among the European physics. Yet his instincts were contraction as his own unyielding logic very first to enrol as an Individual Ordi­ (in English terminology) essentially as government advisor on science policy nary Member and was a member of the those of an engineer, and he had no time was applied to his former creation. organizing committee of the 1st General for the single-minded unworldliness that Although a subtle advocate of the pro­ Conference, in Florence, chairing the he saw in some of his "purer" collea­ jects he believed in — a master of the sessions on quantum electronics and gues. understatement and throw-away line — optics. Later, he was a delegate for the He came to the accelerator field from he was not comfortable in the corridors Individual Ordinary Members on the radar development and worked on the of politics, lacking the patience to sup­ Council, and the first chairman of EGAS Harwell 180 MeV synchro-cyclotron port those he considered inconsistent or which was to become the Atomic Spec­ where his exceptional design talents the total commitment that can some­ troscopy Division and then a Section of were quickly marked by J.D. Cockcroft times be required. the Atomic Physics Division of EPS. His who subsequently encouraged him to His recall to CERN to unscramble the continuous fight for peace, against any be one of the first to join the new problems of the SPS and then to build kind of oppression and for human rights organisation, CERN. There he concen­ the machine in the wake of R.R. Wilson's is well known and was an essential trated on the design of the 25 GeV pro­ scintillating performance at the Enrico aspect of his personality. ton synchrotron (PS), taking over in Fermi Laboratory in the USA, allowed 1954 the Department which built the him to display both his organisational REFERENCES machine. His first appointment as Direc­ and design talents to the full. His style 1. Brossel J. and Bitter F., Phys. Rev. 86 tor-General, 1960-61, came when he was distinct: having kept his options (1952) 308. was already preparing his return to open to the last possible moment, he 2. Brossel J. and Kastler A., C.R. Ac. Sc. Paris England, but during that short period he would then present an imperturbable 229 (1949) 1213. established the committee structure firmness. He drove his staff hard but he 3. Kastler A., J. de Physique 11 (1950) 255. that was to regulate so effectively the had the knack of treating them as people and retaining the common touch and a sense of humour. Not everyone agreed THE FACULTY OF SCIENCE AT THE UNIVERSITY OF with his way of doing things, but none FRIBOURG - SWITZERLAND would gainsay his astonishing grasp of HAS AN OPENING, EFFECTIVE AUTUMN 1984, FOR THE POSITION OF A all aspects of accelerator design and his genius for elegant solutions to engineer­ FULL PROFESSOR IN EXPERIMENTAL PHYSICS ing problems. He was knighted in 1981. The successful candidate is expected to teach in French and/or In recent years, with the SPS perform­ German and to lead experimental research in a field different from ing in a class of its own, Sir John was nuclear, particle and medium energy physics. much occupied with consultancy work Applications should include curriculum vitae, report on scientific related to the scientific and technical activities with list of publications (a few selected reprints) and should be addressed to the: programmes of the European Communi­ Dean of the Faculty of Science ties. Europe is the poorer for the sum­ University of Fribourg, Pérolles, CH - 1700 Fribourg / Switzerland mary curtailment of his services in this Closing date for applications is 31 JULY, 1984. The Dean may be capacity. contacted for further information. E.N. S h aw 15