Assessing different forms of the strong-field approximation for harmonic generation in molecules

We analyse three different formulations of the strong-field approximation for high-harmonic generation in diatomic molecules, based on length, velocity and acceleration form for the recombination amplitude. We compare the predictions for the two-centre interference with those from the time-dependent Schrodinger equation. We nd that the velocity form gives the closest agreement with the exact results while being the simplest from a computational point of view.