We have performed calculations of attosecond laser-atom interactions for laser intensities where interesting two and three photon effects become relevant. In particular, we examine the case of hole burning in the initial orbital. Hole burning is pres
ent when the laser pulse duration is shorter than the classical radial period because the electron preferentially absorbs the photon near the nucleus. We also examine how 3 photon Raman process can lead to a time delay in the outgoing electron for the energy near one photon absorption. For excitation out of the hydrogen $2s$ state, an intensity of $2.2times 10^{16}$ W/cm$^2$ leads to a 6 attosecond delay of the outgoing electron. We argue that this delay is due to the hole burning in the initial state.
We present direct measurements of the hyperfine splitting of Rydberg states in rubidium 87 using Electromagnetically Induced Transparency (EIT) spectroscopy in a room-temperature vapour cell. With this method, and in spite of Doppler-broadening, line
-widths of 3.7 MHz FWHM, i.e. significantly below the intermediate state natural linewidth are reached. This allows resolving hyperfine splittings for Rydberg s-states with n=20...24. With this method we are able to determine Rydberg state hyperfine splittings with an accuracy of approximately 100 kHz. Ultimately our method allows accuracies of order 5 kHz to be reached. Furthermore we present a direct measurement of hyperfine-resolved Rydberg state Stark-shifts. These results will be of great value for future experiments relying on excellent knowledge of Rydberg-state energies and
