The carrier envelope phase (CEP) is a crucial parameter for a few-cycle laser pulse since it substantially determines the laser waveform. Stepping forward from infrared (IR) to extreme ultraviolet (EUV) pulses, we propose a strategy to directly characterize the CEP of an isolated attosecond pulse (IAP) by numerically simulating the tunneling ionization of a hydrogen atom in a combined IAP and phase-stabilized circularly polarized IR laser pulse. The fine modulation of the combined laser fields, due to the variation of the CEP of the IAP, is exponentially enlarged onto the distinct time-dependent tunneling ionization rate. Electrons released at different time with distinct tunneling ionization rates are angularly streaked to different directions. By measuring the resulting photo-electron momentum distribution, the CEP of the IAP can be retrieved. The characterization of the CEP of an IAP will open possibilities of capturing sub-EUV-cycle dynamics.

© 2016 Optical Society of America

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