Attosecond time-scale intra-atomic phase matching of high harmonic generation

Using a model of high-harmonic generation that couples a fully quantum calc ulation with a semiclassical electron trajectory picture, we show that a ne w type of phase matching is possible when an atom is driven by an optimal o ptical waveform. For an optimized laser pulse shape, strong constructive in terference is obtained in the frequency domain between emissions from diffe rent electron trajectories, thereby selectively enhancing a particular harm onic order. This work demonstrates that coherent control in the strong-held regime is possible by adjusting the peaks or a laser held on an attosecond time scale.