Isotope-selective ionization utilizing molecular alignment and non-resonant multiphoton ionization

We demonstrate laser nitrogen isotope separation, which is based on field-free alignment and angular-dependent ionization of 14N2 and 15N2 isotopologues. A linearly polarized short laser pulse (λ ~ 795 nm, Δτ ~ 60 fs) creates rotational wave packets in the isotopologues, which periodically revive with different revival times as a result of different moments of inertia. Another linearly polarized short laser pulse (λ ~ 795 nm, Δτ ~ 60 fs) ionizes one of the isotopologues selectively as a result of their different angular distributions. In the present experiments, the ion yield ratio R [=I(15N2+)/I(14N2+)] can be changed in the range from 0.85 to 1.22, depending on the time delay between the two laser pulses.