We theoretically investigate the generation of intense keV attosecond pulsesin an orthogonally polarized multicycle midinfrared two-color laser field. Itis demonstrated that multiple continuum-like humps, which have a spectral widthof about twenty orders of harmonics and an intensity of about one order higherthan adjacent normal harmonic peaks, are generated under proper two-colordelays, owing to the reduction of the number of electron-ion recollisions andsuppression of inter-half-cycle interference effect of multiple electrontrajectories when the long wavelength midinfrared driving field is used. Usingthe semiclassical trajectory model, we have revealed the two-dimensionalmanipulation of the electron-ion recollision process, which agrees well withthe time frequency analysis. By filtering these humps, intense isolatedattosecond pulses are directly generated without any phase compensation. Ourproposal provides a simple technique to generate intense isolated attosecondpulses with various central photon energies covering the multi-keV spectralregime by using multicycle driving pulses with high pump energy in experiment.
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