Novel characterization method for an isolated attosecond pulse by using CEP dependence

We demonstrate a new measurement method for characterizing an isolated attosecond pulse. Traditionally, attosecond pulses are measured by photoelectron streaking, which relies on two-photon ionization using a secondary laser pulse. Recently, in situ measurement of attosecond pulses was accomplished by perturbing high harmonic generation process with a weak laser field in the nonlinear medium. Here, we demonstrate a novel attosecond measurement method without the need of a photoelectron source or a secondary laser pulse. Instead, we utilize the strong carrier-envelope-phase (CEP) sensitivity of the attosecond pulse generation process by a few-cycle driver. Effectively, the CEP-dependent modulation on the spectrum of the attosecond pulse can be explained by the time-domain grating diffraction. When a light irradiates few grooves on a grating, the far-field diffraction pattern is extremely sensitive to the groove position. Analogously, the narrow envelope of the few-cycle driver serves as a temporal grating and the CEP implies the relative position of the grating lines. We use this to measure the attosecond pulse. Consequently, we confirm our measurement method in experiment and theoretically show its validity for the measurement of a broadband attosecond pulse.