Field-free alignment in repetitively kicked nitrogen gas

We demonstrate a high level of laser-induced transient alignment in room temperature and density N-2 with a technique that avoids laser field ionization. Our measured alignment shows an improvement over previous one-pulse or two-pulse experimental alignment results and approaches the theoretical maximum value. We employ eight equally spaced ultrafast laser pulses with a separation that takes advantage of the periodic revivals for the ensemble of quantum rotors. Each successive pulse increases the transient alignment [< cos(2) theta >(t)] and also moves the rotational population away from thermal equilibrium. These measurements are combined with simulations to determine the value of < cos(2) theta >, the J-state distributions, and the functional dependencies of the alignment features.