Multiphoton Ionization

Multiphoton ionization happens in an intense light beam when atoms absorb more than one photon. In strong fields an atom may absorb not only the minimum energetically necessary number of photons for ionization, but also excess photons. The last process is the so called “above threshold ionization” (ATI) which as well as “normal” multiphoton ionization (MPI) takes place in the strong laser fields. Both processes are between those responsible for the energy transfer from the laser to the plasma. The paper deals with the quantum mechanical calculation of MPI and ATI of atomic hydrogen. At the moderate intensities of light these processes may be treated by methods of perturbation theory.

Light-modulated reflectance in CdS

Reflectance spectra of CdS modulated by a second, intense light beam, show detailed structure due to excitons. This structure results from screening induced by the free carriers generated by the intense light beam. By maximizing the effect we were able to obtain considerably better resolved spectra than previous photo- or electro-reflectance measurements had given. A good theoretical fit was possible with a choice of reasonable parameters.