Enhanced harmonic generation in extended molecular systems by two-color excitation

Numerical simulations of high-order harmonic generation in the molecular ions H₂⁺ and H₃²⁺ show that two-color intense (I10¹⁴W/cm²) short (<1-psec) laser pulse excitation produces harmonics at large internuclear distances with larger efficiencies (intensities) at 6Uₚ, 8Uₚ, and 10Uₚ energies than in single-atom single-frequency excitation. The two-color excitation scheme creates efficient high harmonics by first ionizing electrons with a high-frequency laser pulse and accelerating them with lower frequency towards neighboring atoms. Such two-color schemes should be useful for enhancing high-order harmonic generation in clusters.