Enhanced generation of attosecond pulses in dispersion-controlled hollow-core fiber

We describe theoretically the enhanced generation and propagation of attosecond pulses in a gas medium irradiated by sub-10-fs laser pulses. Both classical and quantum calculations reveal a significant increase in the energy of the attosecond pulse as a result of quasiphase matching in a tapered structured hollow-core fiber. The increasing laser field into the fiber reduces the dependence of the harmonic spectrum on the dispersive phase of the laser pulse and ensures generation and propagation of a single attosecond pulse in a highly ionized transient plasma. For the attosecond pulse radiation this design acts as a phase-locked traveling-wave x-ray laser.