The growth of the group in the 1960s

It is important to remember that, at that time, nearly all funding sources available for preparing a doctoral thesis (as CNRS research interns or university assistants) were temporary and offered no possibility for promotion. After obtaining their degrees, new doctors had to seek positions elsewhere (this situation would change with the establishment of third-cycle doctoral programs and assistant professor positions). Additionally, there was a long-standing tradition in universities of appointing professors in provincial institutions before they could apply for positions in Paris. Thus, the first five doctors mentioned, up until 1960, left the laboratory after completing their theses.

From the beginning of the 1960s, a new phenomenon emerged that would significantly contribute to the development of the group: an increase in the creation of researcher positions at the CNRS and teaching positions in universities. This was a response to the societal changes that led the children of the middle classes to pursue university studies in large numbers and to support the larger generations emerging after the Liberation. Claude Cohen-Tannoudji and Marie-Anne Bouchiat were the first to benefit from this evolution, which allowed them to secure stable positions at the laboratory.

Thus, Claude and Marie-Anne took on young “tricyclists” or doctoral students after their third cycle, supervising their work and no longer depending on Jean Brossel. This marked the beginning of a structured team approach, which would become systematic by the end of the 1960s and the beginning of the 1970s.

Many of the ongoing studies continued the earlier work: double resonance, pumping, relaxation in all types of collisions, level crossings… Following the methods of electronic bombardment (by Pébay-Péroula and Descoubes), an ion bombardment was attempted, where much heavier projectiles were less disturbed by magnetic fields (Jean-Pierre Faroux with Claire Lhuillier and Nicolas Billy).

However, it was in the second half of the 1960s that a diversification of research topics began to take shape. Lasers were utilized for coherent optical pumping (Bernard Decomps and Michel Dumont built their own helium-neon lasers) and for diffusion studies (Marie-Anne Bouchiat and Pierre Lallemand returned from the United States in 1966 with a thesis prepared under Bloembergen).

The highlight of this era was, of course, the year 1966, with the award of the Nobel Prize in Physics to Alfred Kastler. It was a great joy for all members of the laboratory. Kastler’s joy was tempered by his regret that the prestigious jury did not understand the indistinguishability—or rather the “non-separability”—of the two laboratory leaders and did not associate Brossel’s name with his. He would repeat this on many occasions, both public and private, with a sincerity that excluded any suspicion of false modesty.

A few days after the announcement of the Prize, Kastler organized a new collective photography session. However, the small room used in 1956 was far too small. Everyone had to squeeze onto the wide porch of the building on Rue Lhomond. Thirty people surrounded Kastler and Brossel, including about ten engineers and technicians, and around twenty physicists. The only three individuals missing from this photograph were Jean-Claude Lehmann (whose thesis was nearing completion), Jacques Meunier, and Michèle Glass-Maujean; they were among the youngest.

Overall, it was a young population. Of this group of twenty physicists, only three were already state doctors (Claude Cohen-Tannoudji, Marie-Anne Bouchiat, and Bernard Cagnac, who returned to the laboratory after five years of “exile” in Orsay). Excluding four young “tricyclists” (Haroche, Ducloy, Dupont-Roc, Pottier), the vast majority were in the process of completing their doctoral thesis (including two nearing completion: J.P. Descoubes and F. Hartmann), although some had already obtained their third-cycle degrees. For reference, third-cycle doctoral programs began to replace higher education diplomas starting in 1960.

Of the approximately twenty doctoral students working in the laboratory in 1966, about half later dispersed to Orsay (Françoise Grossetête), Nice (Nicole Polonsky-Ostrovsky), Grenoble (Hartmann, then Romestain), or Paris-Nord (Decomps, Dumont, Ducloy together in 1973, and later Barbé). A large portion remained at the laboratory longer, ensuring the supervision of new members and the transmission of knowledge and techniques acquired during their theses. However, further dispersals occurred later, depending on the evolution of research themes. By the year 2000, only a third of these doctoral students were still part of the laboratory. This is a very different situation from the early years (up to 1960): the dispersion rate dropped from 100% to around 45% after obtaining a doctorate. However, it could reach as high as 70% in the long term. What is the desirable rate of dispersal to ensure the continuity of acquired knowledge while avoiding the risks of excessive inbreeding?

The excitement surrounding the Nobel Prize led to a negative consequence during the year 1967, fortunately temporary. Alfred Kastler fell victim to the overwhelming availability to everyone, which was one of the characteristics of his personality. His exquisite politeness did not provide any barrier to the swarm of journalists or organizers of various meetings who came to solicit him, overloading him and leading to a certain exhaustion.

To reduce this overload, Kastler decided—despite his passion for teaching—to leave his position as a professor at the university for a position as a research director at the CNRS starting on October 1, 1968. Thus, he never taught his last courses (on thermodynamics, that year) at the university. When he returned from a scientific tour abroad after Easter 1968, it was already May and the time of student revolution. Nonetheless, he managed the impressive feat of obtaining a calm, attentive, and serene atmosphere in a frenzied and overcrowded lecture hall. He projected a photo of Boltzmann’s grave in the Vienna cemetery as an illustration of his final message about the role and values of science. This was a moment of respite amidst the university turmoil of 1968. It is certain that this “tour de force” would not have been possible without Kastler’s recognized commitment to defending the great causes and values of our society.