All-optical frequency-resolved optical gating for isolated attosecond pulse reconstruction

We demonstrate an all-optical approach for precise characterization of attosecond extreme ultraviolet pulses. An isolated attosecond pulse is produced from high-order harmonics using an intense driving pulse with a proper gating technique. When a weak field is synchronized with the driver, it perturbs the harmonics generation process via altering the accumulated phase of the electron trajectories. The perturbed harmonic spectrum can be formulated as a convolution of the unperturbed dipole and a phase gate, implying the validity of complete reconstruction of isolated attosecond pulses using a conventional frequency-resolved optical gating method. This in situ measurement avoids the central momentum approximation assumed in the widely used attosecond streaking measurement, providing a simple and reliable metrology for an isolated attosecond pulse.