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Contains fulltext : 19299_impuinofh.pdf (Publisher’s version ) (Open Access) This thesis describes research on the interaction between electromagnetic radiation and matter. In most situations, a photon picture is used in describing the interaction between radiation and matter; radiation is considered a stream of photons with an energy determined by the wavelength of the light. During the interaction between light and matter, these photons are absorbed or created. In our experiments, ultra short light pulses have been generated with a pulse duration of 0.5-1 picoseconds consisting of one single half-cycle. The matter, we have chosen, are Rydberg atoms, in which the outer electron is excited to a highly excited state. The roundtrip time of the Rydberg electron around the core is long (picoseconds). Hence, the interaction between the half-cycle pulse and a Rydberg atom is shorter than the electron orbiting time and this interaction is described as impulsive. The half-cycle pulse kicks the electron in the direction defined by the electric field of the light. In contrast to other situations, the energy absorbed or liberated is not only determined by the field strength of the half-cycle pulse but also by the velocity direction of the electron at the moment of the kick. The electric field strength is crucial and not the photon energy. This impulsive character makes a description of the interaction of a half-cycle pulse with a Rydberg electron in classical Newtonian mechanics possible. We have used these half-cycle pulses to manipulate the electron motion in atoms, and created a special kind of electronic wave packet. We have combined half-cycle pulse excitation with a technique to measure the velocities of the electrons when these are kicked out of the Rydberg atom. The technique is called velocity map imaging, a University of Nijmegen invention. This combination has made it possible to determine directly the wave function of the Rydberg electron in momentum space 127 p. |
