Abstract

We demonstrate enhancement by 1 order of magnitude of the high-order harmonics generated in argon by combining a fundamental field at $1300\mathrm{nm}$ (${10}^{14}\mathrm{W}{\mathrm{cm}}^{-2}$) and its orthogonally polarized second harmonic at $650\mathrm{nm}$ ($2\times {10}^{13}\mathrm{W}{\mathrm{cm}}^{-2}$) and by controlling the relative phase between them. This extends earlier work by ensuring that the main effect is the combined field steering the electron trajectory with negligible contribution from multiphoton effects compared to the previous schemes with $800/400\mathrm{nm}$ fields. We access a broad energy range of harmonics (from $20\mathrm{eV}$ to $80\mathrm{eV}$) at a low laser intensity (far below the ionization saturation limit) and observe deep modulation of the harmonic yield with a period of π in the relative phase. Strong field theoretical analysis reveals that this is principally due to the steering of the recolliding electron wave packet by the two-color field. Our modeling also shows that the atto chirp can be controlled, leading to production of shorter pulses.

© 2010 Optical Society of America

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