The end of the 20th century

It is important to mention the year 1972, marked by the retirement of the CNRS research director, Alfred Kastler. Since he continued to frequent the laboratory regularly—and considering the “inseparability” of the two heads—this change did not alter daily life in any way. Perhaps, as noted in the activity reports that followed, there was a clearer emphasis on structuring into teams.

A significant date was 1984. Indeed, in the autumn of 1983, we found Alfred Kastler very fatigued by worsening heart failure, which was considered inoperable given his age. He then retired to Bandol, at the home of his eldest son, Daniel (a professor of theoretical physics at the University of Marseille-Luminy). He passed away there on January 7, 1984. A year later, a symposium was jointly organized by the ENS and the CNRS (the M.P.B. department – Basic Mathematics and Physics – then headed by Jean-Claude Lehmann). The event gathered around one hundred scientists from around the world whose work had been connected to that of Alfred Kastler, on January 9, 10, and 11, 1985. The Prime Minister at the time, Laurent Fabius, personally attended the solemn closing session held on the morning of Saturday, January 12, in the grand amphitheater of the Sorbonne, in the presence of several hundred students.

However, what also made 1984 an important turning point for the Laboratory was the retirement of its director, Professor Jean Brossel. The structure lost both of its founding fathers that same year. Jacques Dupont-Roc bravely took over the direction of what was still the Hertzian Spectroscopy Laboratory of the ENS. Among the small changes that occurred due to this succession, a laboratory council was established following CNRS regulations, which had not existed before. Nevertheless, the structure maintained its vitality and its potential for branching out and renewal.

In 1986, Jean-Claude Lehmann left for research at Saint-Gobain (after his time as head of the M.P.B. department). His disciple, Jacques Vigué, replaced him as head of the Reactive Collisions team until his move to Toulouse with Bertrand Girard in 1990 and 1991. Gérard Gouédard joined the University of Cergy-Pontoise (Michel Broyer had already moved to Lyon shortly after his thesis). Michèle Glass remained the only one in the laboratory interested in molecules. She would, in turn, branch out at the end of the 1990s to take over the Jussieu collision laboratory on the fifth floor of Tower 12.

In 1987, the majority of the Light Diffusion teams branched off to form a new laboratory of statistical physics under the direction of Pierre Lallemand, with Jacques Meunier and Dominique Langevin. At the same time, Anne-Marie Cazabat joined Pierre-Gilles de Gennes’ laboratory at the Collège de France, while Claire Lhuillier moved to the Liquid Physics Laboratory at Jussieu, of which she would become the director a few years later.

In contrast, three new teams were created during the same period:

– The Nonlinear Optics team with Gilbert Grynberg, who returned from the Quantum Optics Laboratory at the École Polytechnique (Palaiseau) in 1983. Unfortunately, Gilbert was struck by the growth of a tumor that led to blindness, a battle he fought with extraordinary courage before passing away in 2003.
– The Dynamics of Coulomb Systems team with Jean-Claude Gay and Dominique Delande, established the same year, but whose development was hindered by the illness and eventual passing of Jean-Claude Gay in 1992.
– The Quantum Optics team with Claude Fabre and Elisabeth Giacobino. Established in 1986, it played with Heisenberg’s uncertainty principle to reduce the quantum noise of photons, eventually creating twin photons… The significance and variety of new themes emerging in this research area quickly led to its division into two distinct groups.

One clear observation from this entire history is that the evolution of research themes over the past twenty years had led to a drastic reduction in the use of radio frequencies. Lasers now provide electromagnetic waves as coherent as radio waves in the 1950s and offer the same potential for applications. This was one of the reasons Jacques Dupont-Roc prepared for the laboratory’s name change, which became the Kastler Brossel Laboratory on January 1, 1994.

It was noted that the laboratory was open to welcoming women. This was emphatically confirmed by the appointment of the next two directors: Michèle Leduc and then Elisabeth Giacobino. The latter passed the baton to Franck Laloë when she became director of the S.P.M. – Physical and Mathematical Sciences – department of the CNRS in 2001.

We will not elaborate on the last fifteen to twenty years in as much detail. Indeed, those more recent years can still be considered not entirely part of the past. Their history will have to be written in turn a little later. We will conclude with the most important event of the last decade: the awarding of the Nobel Prize to Claude Cohen-Tannoudji in 1997, thirty-one years after Alfred Kastler. The dressed atom has demonstrated its power by allowing the calculation of subtle effects that slow atoms down, cool them to extremely low temperatures (a millionth of a degree), enable them to be manipulated in various ways, and truly trap them in light traps. This story is just beginning.