Enhancement of bichromatic high-order-harmonic generation with a high-frequency field - art. no. 023415

Using a high-frequency field superposed to a linearly polarized bichromatic laser field composed by a wave with frequency omega and a wave with freque ncy 2 omega, we show it is possible to enhance the intensity of a group of high harmonics in orders of magnitude. These harmonics have frequencies abo ut 30% higher than the monochromatic-cutoff frequency, and, within the thre e-step-model framework, correspond to a set of electron trajectories for wh ich tunneling ionization is strongly suppressed. Particular features in the observed enhancement suggest that the high-frequency field provides an add itional mechanism for the electron to reach the continuum. This interpretat ion is supported by a time-frequency analysis of the harmonic yield. The ad ditional high-frequency field permits the control of this group of harmonic s leaving all other sets of harmonics practically unchanged, which is an ad vantage over schemes involving only bichromatic fields.