Paul Soleillet

Paul Soleillet (1902-1992) is a little-known French physicist that made seminal contributions to fluorescence anisotropy and polarimetry in his PhD dissertation.

This is the title Paul’s Soleillet PhD dissertation. It is published in Annales de physique 12, 23 (1929) [check in your library because I don’t think it can be found online].  Despite he is an almost unknown scientist, this publication  can be considered the foundational work of Mueller matrix polarimetry. Notably  this was many years before that Hans Mueller at MIT popularized his matrices! Soleillet’s thesis can be also considered as one of the founding works (together with several other publications by his friend Francis Perrin) of fluorescene anisotropy. In fact, Francis Perrin should be also considered as one of the fathers of Mueller matrix polarimetry with his great  paper F. Perrin, “Polarization of light scattered by isotropic opalescent media,” J. Chem.Phys. 10, 415–427 (1942).

There is at least one book  [C. Brosseu in E. Wolf, Progress in Optics, volume 54, 2009] that erroneously attributes this photo to “our” Paul Soleillet. This image corresponds to his uncle, the explorer Paul Soleillet.

I have not been able to find any photo of “our” P. Soleillet. If you have one please share it with me (oarteaga’at’, I would like to include it here.

Below I post the original and the translation of a biographical note about P. Soleillet published in 1994 by the Association des anciens élèves et amis de l’ENS and authored by J. C. Pecker. I apologize from the beginning because this  is not a very good translation.

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Soleillet (Paul), born in Marseille March 13, 1902, died in Paris on 4 August 1992. -Promotion of 1919.

Soleillet Paul was born in Marseille, March 13, 1902. He sometimes joked: “This century had two years “. … A family of teachers, … and explorers. His father was teacher in technical education, his mother taught mathematics. An uncle, Paul Soleillet, which he was given the first name, was a brave explorer of the Sahara and Ethiopian.

After graduating high school in Marseille, he joined rue d’Ulm in 1919, in one of those promotions after the first World War, where, with the joy of life, found himself the passion of education and of research […]. Soleillet, discreet and optimistic, then shared the passions of his classmates, especially physicists: Auger, Couderc, Kirrmann, from his promotion, or the following promotions, Morand, Bayen, Kastler, until aggregation of Physics in1923.

Optics is what ultimately occupied his entire career in various forms. He become – he had this chance! –  associate-trainer at the school. He mostly worked with Henry Abraham and Eugene Bloch. His thesis, dedicated to Paul Langevin, deals with the polarization of the light in the phenomena of fluorescence. This work was mainly theoretical, but Soleillet in this hot atmosphere of the school labs, “experimeted” too. This brilliant thesis is defended on April 11th, 1929, under the chairmanship of Jean Perrin. The “Examiners” are Eugene Bloch and Leon Brillouin. Paul Soleillet was immediately appointed lecturer in Strasbourg, in mathematical Physics, then, in 1937, professor at the University of Poitiers. During the winter of 1940, Soleillet helped organize a laboratory of photoelectricity in the CNRS. Then he chose Paris in 1945, first as lecturer,  in the PCB, an obliged purgatory, then as a professor at the Sorbonne in 1952, in the chair of Physics Quanta … In 1953 he directed different direct thesis work, and settled in the group of Daniel Chalonge at the Institut d’Astrophysique, until his official retirement in 1972. But could he leave this wonderful world of research? He tirelessly continued his work until the lastdays in the laboratory of Atomic and Molecular Physics of the Collège de France by his friend Francis Perrin, and then the Particle Physics laboratory of Professor Marcel Froissart, in the same institute.

He did teaching activities at Strasbourg, Poitiers, Paris and also, but for a few time, he was examiner of Physics at the entry examination to the Ecole Polytechnique, and the initiator of a certificate of applied mathematical physics (“LDCs”) at the Sorbonne. The writer this has not had the chance to follow courses by Paul Soleillet, but at least he had the opportunity to browse through the notes and “Handouts” of Paul Soleillet on quantum mechanics and relativity. Soleillet loved teaching, it can be feel from the first lines in the notes. And he was loved by students who appreciated his good nature, and its wide availability. Sadly he never wanted to make a complete treatise from his classes, and his teaching work has in fact never been published!

The research by Paul Soleillet deal in his first part of his scientific career was about  the physics of optical resonance. If his thesis was mainly theoretical, we should not forget that his manual dexterity was great, and he was a great experimenter. […] Soleillet was one of the first users of light amplifiers to electron multiplication. The purpose of the research was still studying the mechanisms essential of resonance. What was the life of the excited atoms? Two methods were used: the evolution of emission by a collimated jet of atoms (in this case Cd and Zn); and degree of polarization of the light emitted, in a initially zero magnetic field . The controversy generated by the work of Soleillet added prominent difficulties to the  work, but were the conclusions of Soleillet those that eventually imposed. Then, Soleillet studies the influence of the magnetic field and the Zeeman components, he specifies the probability of transition from one level to another and found a low value for the probability of intercombination lines […]. We may note here the opinion of two masters of physics at the time: Yves Rocard said: “In this field trial, Paul Soleillet has pioneered … but we must assert the importance of his work in the theoretical domain … Can say that the work of Perrin and Alfred Kastler rely heavily on results obtained by Soleillet “. Jean Cabannes presents him as “One of the best physicists that the École Normale has given between the wars. ” Its publications are few (twenty notes to the Proceedings of the Academy ofScience, presented by Aimé Cotton, by Peter Weiss, by Francis Perrin, Frédéric Joliot … and some articles in the Journal of Physics). But these articles show a precise and penetrating mind.

On the occasion of his meetings with other physicists, the creative imagination of Soleillet flied free. One diaphragm interposed in a plane conjugate to the slit of a spectrograph was  baptized as “soleillet”, with small “s”. […] The soleillet allowed the calibration spectrophotometric spectra. The soleillet, widely used by Chalonge and Barbier, was one of the strengths of the success of the absolute spectrophotometry of Chalonge,  that was paragon of precision for 1950-1970’s astronomers – before the CCD was routinely used.  Moreover, Soleillet was one of the first to use the … soleillet, during a mission with the team Chalonge  to the Jungfraujoch Observatory, in the Alps.

The work with his last student, Martha Spitzer-Aronson, opened a new area of investigation for Soleille.In 1960 she had defended a thesis, under the direction of Soleillet, about optical resonance where she studied with the selective reflection  with vapors of zinc and cadmium. Martha received one day remains of stained glass from excavations of the church of Saint-Victor de Marseille. Soleillet was amused at first. Had he not been baptized in this church? Then he really got interested. For twenty years, his research in collaboration with Mrs. Spitzer-Aronson, is concentrated on the application to the study of works of art, methods of resonance optical, but also many other physical techniques. They studied  stained glass, but alsoceramics (mainly Hispanic-Moorish), ancient bronzes …

We know the importance of this kind of research today, in detecting the fake, in dating, in the authentication, as in the work of restoration.

His lasts months were painful. He was not well diagnosed at the beginning of this period, he had to undergo several successive surgeries, and he died in Paris on 4 August 1992.

Paul Soleillet was little known to our physicists today. Although his work made he won a price in 1937,  under the report by Paul Langevin: the Hughes Award from the Academy of Sciences. We sometimes sometimes met Soleillet  in the corridors of the Institut d’Astrophysique, then in those of the Collège de France. He was always affable and charming, he had always had high modesty and a great discretion. His life had been marked, I believe that in Strasbourg, by a very cruel family drama. Is this fact that led him to withdrawn into himself? He never put himself forward, he never wanted to impose. But his great charm, humor, smiling, his natural kindness, his enthusiasm still juvenile, remain in the memory of those who, like me, have had the rare opportunity of working with him, and to know him.

Jean-Claude PECKER