High harmonic production can be dramatically increased by utilizing an interaction region much longer than a coherence length. Counter-propagating light pulses can be used to disrupt the out-of-phase harmonic emission from selected zones in the focus so that the remaining emission builds constructively. Counter-propagating light creates a standing field modulation repeating over a half laser wavelength in which phase cancellations for harmonic emission occur. A simple power-law model is used to demonstrate how such pulses can be designed to counteract geometrical phase mismatches and improve emission for individual harmonics by more than two orders of magnitude.

We show the both amplitude and spectrum dynamics of few-cycle laser pulses in two-photon Raman-type self-induced transparency in Ar+ ions, that permit to generate half-cycle laser pulses (FWHM) with more high amplitudes and photon energy as well as spectral widths.

The resonance generation and propagation of single as well as double attosecond pulses in Ar+ are presented by the numerical simulations. Two-photon Raman-type self-induced transparency of the pulses is investigated.

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