WAVELENGTH DEPENDENCE OF HARMONIC-GENERATION EFFICIENCY AT METAL-SURFACES INDUCED BY FEMTOSECOND TI-SAPPHIRE LASER-PULSES

Second and third order harmonics of high intensity (similar to 10(10) W/cm(2)), femtosecond Ti:sapphire laser pulses were generated at a gol d surface. The spectral dependence of the second harmonic generation e fficiency was measured as a function of the fundamental excitation wav elengths (780-850 nm). The efficiency is found to decrease significant ly toward the longer wavelengths. This behavior is consistent with the recently observed very low efficiency of the high order harmonic gene ration at infrared wavelengths (1-3 mu m), while contradicting the sin gle particle perturbative theoretical descriptions of the harmonic gen eration process at the vacuum/metal interface.