Ultrafast dynamics in solids

An ultrafast broadband spectroscopic technique (350 to 900 nm) is employed to measure the dielectric function of GaAs in response to a 70-fs laser pulse excitation. We observe drastic changes in the dielectric function within 1ps of the excitation, which we attribute to an ultrafast non-thermal structural transition. These broadband measurements provide extensive information on the initial electronic excitation and the dynamics of the subsequent phase transition.

In this talk we present the coherent excitation and coherent control of the A1 phonon mode in Te. First, the underlying theory about the excitation of the A1 phonon mode, and only this, in a certain class of materials is discussed. The theory, called Displacive Excitation of Coherent Phonons (DECP), predicts the excitation of the A1 phonon mode as a result of electronic excitation following absorption of an ultrashort laser pulse by the material. Since there is no symmetry breaking mechanism in the electronic excitation through absorption the effect can only take place in materials which... Read more about Ultrafast Phase Transitions in Solids

Time is of philosophical interest as well as the subject of mathematical and scientific research. Even though it is a concept familiar to most, the passage of time remains one of the greatest enigmas of the universe. The philosopher Augustine once said: "What then is time? If no one asks me, I know what it is. If I wish to explain it to him who asks me, I do not know." The concept time indeed cannot be explained in simple terms. Emotions, life, and death - all are related to our interpretation of the irreversible flow of time. After a discussion of the concept of time, we will review... Read more about Stopping time