Strong-field molecular ionization: determination of ionization probabilities calibrated with field-free alignment

International audienceWe report an original optical method providing the probability of molecular ionization induced by femtosecond laser pulses. The approach consists of exploiting molecular alignment in order to extract reliable information about ionization. The cross defocusing technique implemented for this purpose reveals a sensitivity with respect to post-pulse alignment, as well as to free electron density induced by the ultra-short laser pulse. The analysis of the resulting signal gives thus access to absolute single-ionization probabilities calibrated through the degree of alignment provided that free electrons are mainly produced from single-ionization. The relevance of the method is assessed in N2