The ultra-fast control of materials by light is a major challenge. By using a femtosecond laser flash, it is thus possible to generate spectacular changes in the physical properties of materials (ferroelectricity, conductivity, magnetism, photochromism, etc.) on ultra-fast time scales (fs or ps). The development of time-resolved experimental techniques makes it possible to follow in real time the dynamics of the elementary constituents of matter or of various degrees of freedom – such as electronic, molecular, crystalline structures or even symmetry – which are at the origin of the emergence of many functions. Moreover, it is possible to selectively excite a specific degree of freedom to optimize the photoinduced transformation process, non-equilibrium by nature. It is therefore essential to combine complementary techniques sensitive to these different degrees of freedom to gain a global understanding of their dynamics and their couplings, leading to a multi-scale transformation from molecule to material.
Institut de Physique de Rennes, Univ Rennes, CNRS – UMR 6251, F-35000 Rennes, France