Ultrafast light-matter interaction: Measuring and controlling quantum dynamics with attosecond and femtosecond flashes of light
Ultrafast light-matter interaction is an exciting aspect of modern quantum physics, directly resolving the fastest motion of electrons inside and in between atoms and molecules that constitute the matter that is surrounding us, where the coherence times can be as short as femtoseconds (10-15 s) or even attoseconds (10-18 s). Strong laser fields are available as pulsed flashes of light, with durations of only a few optical oscillation periods in the single-digit femtosecond regime, and an electric field strength that becomes comparable to the electromagnetic binding forces within atoms and molecules. These pulses allow one to measure, understand and control the electron dynamics in natural quantum systems at a fundamental level. In combination with new attosecond light sources at extreme ultraviolet and x-ray wavelengths, derived from high-order harmonic generation or at (x-ray) free-electron laser facilities, this allows one to obtain dynamic fingerprints that are very specific for each atomic species (i.e., time-resolved ultrafast x-ray spectroscopy).
In this lecture series I will give a basic introduction into the physics of ultrafast light-matter interaction with strong laser fields. We will discuss the relevant tools needed for this type of research, how attosecond pulses can be produced in a laser laboratory, and how ultrashort intense x-rays can be produced with free-electron lasers at facilities like FLASH/DESY or European XFEL. In particular we will discuss the ultrafast absorption response of atoms and molecules, how absorption spectra develop on the ultrafast timescale (obeying the Fourier time-bandwidth uncertainty), and learn how strong fields can be utilized to control this response. We often use the helium atom as a natural platform for an entangled quantum system with its two active electrons, which allows us to learn more about Fano resonances and femtosecond autoionization dynamics. We will also discuss very new findings such as how a short-lived population inversion of this correlated two-electron system can be achieved with femtosecond pulses from a free-electron laser.