Systematic study of high-order harmonic optimal control by temporal pulse shaping of laser pulses

We explore experimentally and numerically the physics underlying the optimization of high-order harmonic generation by intense laser pulses, whose temporal profile is tailored by a learning genetic algorithm. Based on a large set of optimization data obtained under different generation parameters, we show that the algorithm converges toward a class of very special profiles on the leading edge of the pulse. The behavior of the harmonic signal is then compared with theoretical simulations based on the time-dependent Schrödinger equation, allowing one to identify separately the role of microscopic and macroscopic phenomena in the temporal dynamics of high-harmonic generation and optimization.