We use a carrier-envelope-phase stabilized sub-2-cycle laser pulse to generate high-order harmonics and study how the two-dimensional spectrum of harmonics, with the resolutions in temporal frequency and spatial frequency, is shaped by the laser phase. An arrowlike spectrum obtained experimentally when the gas cell is located in front of the laser focus point shows a resolution of full quantum trajectories; i.e., harmonics from different trajectories stand on different positions in this spectrum. In particular, due to the laser phase combined with the classical-like action, the harmonics from short and long trajectories differ maximally in their curvatures of wave fronts in the generation area, and so occupy very different ranges of spatial frequency at the far field. The result directly gives a full map of quantum trajectories in high-order harmonic generation. The conclusion is supported by an analytical model and quantum mechanics simulations.

• Received 27 October 2013

DOI:https://doi.org/10.1103/PhysRevLett.113.073601