Toward Optical CYcle DYnamics in Solids
French National Research Agency (ANR)  
Funder: French National Research Agency (ANR)Project code: ANR-19-CE30-0015
Funder Contribution: 698,435 EUR
The goals of the project TOCYDYS (Towards Optical CYcle DYnamics in Solids) are the following : - To carry out an ambitious experimental and theoretical research program, about the ultra-fast dynamics at femtosecond and attosecond time scales, in the domain of solid state physics and laser matter interaction. - Contribute to the sustainability and development of the Equipex Attolab, whose funding expires at the end of 2019, by participating in operating costs and increasing its attractiveness, in particular by offering new experimental tools open to users and visitors. The aim of TOCYDYS' fundamental research program is to investigate the dynamics of solids, with optical cycle resolution, and then to cross the femtosecond limit. We will concentrate on transparent wide band gap dielectrics like silica and quartz (SiO2) or sapphire (Al2O3), but other types of materials, dielectrics, semi-conductor or metallic, can also be integrated in the program. The experiments will be carried out on the recently opened facilities of the Attolab Equipex at LOA and LIDYL. We will have access to phase stabilized and associated ultrashort VUV pulses. The experiment will consist in exciting the samples with pulses of a few optical cycles (intensity of 1012 to 1015 W/cm2) and to probe the dynamics by measurement of reflectivity change, in the IR and visible domains, then with attosecond pulse trains in the VUV. We will have direct access to the physical mechanisms of laser matter interaction and the initial steps of the electronic relaxation of the solid: multiphoton, tunnel or Zener ionization, modulation of the band gap, inelastic diffusion of carriers, impact ionization, Auger effect, etc. During the first part of the program (20 months), measurements will be made in the visible and near IR, with the aim of achieving the resolution of the optical cycle. Then, in the second part, we will build a set-up for reflectivity measurement in the VUV, capable of recording variations of the amplitude of the probe pulse, but also measuring phase shift using spatial interferometry in the VUV domain. In parallel, a theoretical program, able to perform numerical simulations of the pump-probe experiments will be developed. Using ab initio approaches, based on Density Functional Theory and its time dependent counterpart (TDDFT) and the Many-Body perturbation Theory (MBPT), it will take into account the many-body interactions among the electrons of the system, including the screening of the electromagnetic fields due to the microscopic nature of the material and the excitonic effects i.e. interaction between excited electron and the remaining hole. Calculations of increasing difficulties will describe the optical properties of the solid at rest, then modification of the dielectric constant in the excited solid, and finally simulate the pump probe experiments. This project, gathering highly skilled researchers from three different laboratories, namely LOA and LSI at Palaiseau, and LIDYL at Saclay, is a unique opportunity to develop up-to date methods and original methods for solid state physics at the Attolab facility that will be made available for the scientific community. Submitted to the ANR in 2018, the TOCYDYS project has received extremely positive feedback from the referees and was elected on the complementary list. This year we have improved it with a theoretical support that will provide a precious help to interpret the results, understand the physics and guide the future experiments. We sincerely hope that this exciting and innovative research program, which will open new ways for observing and understanding ultrafast phenomena in solids and materials, will receive the necessary founding from ANR.
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