Controlled Asymmetric Photoelectron Emission using Electron Wavepacket Interference

Two-color ionization is a powerful method for characterizing light fields and investigating atomic and molecular physics with attosecond sources based on High Harmonic Generation (HHG). Depending on the time duration of the light fields, two main techniques have been established: streaking [1], appropriate in the regime where a single attosecond pulse is generated, and RABBIT, used instead when a relatively long fundamental pulse generates an XUV pulse train and the variation between consecutive XUV pulses is negligible [2]. In the regime where high harmonics are generated by a few-cycle fundamental pulse, however, both the amplitude and phase of the few resulting XUV pulses vary significantly, and this variation can be controlled by the CEP of the driving IR field [3]. In this work, we use attosecond pulse trains produced by HHG in argon using a 200 kHz-repetition rate, Carrier-Envelope-Phase (CEP) stable, 6-fs OPCPA laser system [4] and detect emitted photoelectrons from helium by a three-dimensional (3D) momentum spectrometer [5]. With our excitation scheme, where a weak replica of the generating IR is overlapped with the short XUV pulse train for photoionization, we investigate the regime between the two limits represented by streaking and RABBIT.