Name: Pascal Salières
Nationality: French
Date of birth: 23 June 1967
Short CV:
1991: Diploma of Engineer of ESPCI, Paris
1995: PhD in Physics, Pierre and Marie Curie University – Paris
2005: Habilitation, Paris-Sud University – Orsay
Current position:
Program leader in Attosecond Science, Laboratory Interactions, Dynamics and Lasers, CEA-Saclay.
When I started my PhD on high-order harmonic generation with Anne L’Huillier in Saclay in 1992, the field was brand new (there was not even an interpretation for this spectacular process) and very challenging! Things went fast from the very beginning: one month later I was performing experiments in Lund (Sweden) on the “cutoff rule”, and 6 months later I settled for one year in Livermore, California. Under the invitation by the National Laboratory, we performed a series of experiments ranging from fundamental studies of the HHG process (ellipticity dependence, spatial profiles) to the first attempt ever to use it as a source in atomic spectroscopy. This was successful behind our expectations since we used up to the 69th harmonic (100 eV!) but led to a massive disappointment when the paper bounced back from a “high-impact factor” journal. This taught me that you should never take for granted that people understand the importance of what you are doing J. This stay in Livermore was an extraordinary experience, both scientific and personal: the lab hosted the most energetic laser in the world and the environment offered everything one could dream of.
Back in France, after two years of continuous experimental work, I turned to simulations to understand all these results. I had the unique opportunity to work simultaneously with Maciek Lewenstein, invited scientist (and soon hired by Saclay), and Anne L’Huillier, and benefited much from these two giants of our field. Studying the interplay between the microscopic and macroscopic responses, I discovered the importance of the dipole phase in determining the spatial and temporal coherence of the harmonic beam. These phase effects have now become central in the field and, with less pride than real satisfaction, I would advise students: “Look at the phase!”
After my PhD defense in 1995, I was appointed by Saclay on a full researcher position to continue this promising research together with Bertrand Carré (Anne L’Huillier leaving for Lund). After optimizing the conversion efficiency up to the microjoule level, we performed a number of characterization and application experiments (such as XUV interferometry for plasma diagnostic) and in parallel, pushed theoretical investigations towards the emerging field of Attophysics. With Philippe Antoine, we studied how attosecond pulses could be generated in a macroscopic medium, and the dipole phase, again, turned out to be a key element. We also performed a series of investigations to identify and control the different quantum-path contributions.
When Pierre Agostini (at that time in Saclay) and Harm Muller measured the first attosecond pulses in Palaiseau in 2001, I soon proposed them to investigate attosecond pulse generation over a much broader spectral bandwidth, as allowed by the Saclay harmonic beamline, developed and optimized over the years together with Hamed Merdji. This led us to the discovery of the atto-chirp in 2003. This atto-chirp is still today the limiting factor for the duration of the attosecond pulses: if compensated, we could generate close to zeptosecond pulses! This also started an exciting series of experiments that extends up to now where we use characterized and optimized attosecond pulses to investigate ultrafast electronic and nuclear dynamics in matter.
Recently, we generated attosecond pulses in aligned molecules with Thierry Ruchon. This turned out to be extremely fruitful since this allows not only a coherent control of the attosecond emission but also a reconstruction of the radiating orbital by quantum tomography. With the latter, in collaboration with theorists at LCPMR-Paris, we demonstrated that it is indeed possible to combine Angström-spatial resolution with attosecond temporal resolution. This opens wide perspectives for this high harmonic spectroscopy.
In parallel, we performed photoionization spectroscopy, e.g., measuring the molecular-frame electron angular distribution to fully characterize the harmonic polarization, with ISMO-Orsay; the painfully-long acquisition times for these coincidence measurements were worth it since they evidenced for the first time a depolarization in the emission. We also investigated with UAM-Madrid resonant ionization with attosecond resolution allowing us to see, in real time, the buildup of a Fano resonance! All these results are opening exciting perspectives!
The above-mentioned achievements are the result of a remarkable team work between the permanent researchers and the students and postdocs, who were the driving force and brought their enthusiasm: Laurent Le Déroff, Jean-François Hergott, Milutin Kovacev, Yann Mairesse, Armelle de Bohan, Marco De Grazia, Willem Boutu, Stefan Haessler, Zsolt Diveki, Antoine Camper, Nan Lin, Bastian Manschwetus, Vincent Gruson, Sébastien Weber, Lou Barreau; many of them are today key players in our field!