Isotope-selective laser molecular alignment

We experimentally demonstrate isotope-selective alignment in a mixture of ¹⁴N₂, ¹⁵N₂ isotopes. Following a strong ultrashort laser pulse rotational excitation, the angular distributions of the isotopes gradually become different due to the mismatch in their moments of inertia. At predetermined times, the desired isotope attains an aligned state while the other component is antialigned, facilitating further selective manipulations by polarized light. By a properly timed second laser pulse, the rotational excitation of the undesired isotope is almost completely removed.