| We proposed and demonstrated a new scheme to produce single, isolated attosecond pulses using laser pulses containing multiple-cycle oscillations. Such laser pulses are much easier to generate and control than the few-cycle pulses that have been used so far. When atoms are driven by multiple-cycle fields, a train of attosecond pulses are emitted. The temporal spacing between the successive pulses is one half of an optical cycle. In our scheme, a weak second harmonic field is added to the driving field to increase the spacing to a full optical cycle. Then a polarization gating is applied to switch out one attosecond pulse from the train. The gate width is two times longer than conventional polarization gating, which significantly reduces the depletion of the ground state making the multiple-cycle driving feasible. |
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