According to Albert Einstein (photoelectric effect 1905), the number of photoelectrons emitted from matter is proportional to the light intensity. In our experiment, we study the highly non-linear process of multiphoton ionisation, where an atom or molecule absorbs many photons in one step. This non-linear process is a hot topic in laser research.

The interaction of highly intense radiation with matter and the corresponding non-linear effects have been subject of lively research, both theoretical and experimental [1.-6.], especially in the infrared and visible photon energy regimes. Laser systems capable of producing high intensities also at photon energies in the (soft) X-ray regime open access to novel effects like non-linear Compton effects or simultaneous elastic and inelastic photon scattering, and allow multiphoton-ionisation experiments in a new domain [4.-6.]. However, experiments have so far relied on time-of-flight mass spectrometry or related methods and have been unable to analyse the reaction products with high accuracy, nor were they able to select or prepare products for further studies in a well-defined way.

We are currently setting up a Penning-trap-based experiment for multiphoton-ionisation of confined particles by highly intense and highly energetic laser light.

The particles (atomic or molecular ions) are confined in a cylindrical Penning trap with conical outer electrodes for access also with highly focused laser light and are subjected to the laser light in a controlled manner.