Linear and nonlinear absolute phase effects in interactions of ultrashort laser pulses with a metal nano-layer or with a plasma layer

It has been shown that in the scattered radiation, generated by an ultrashort laser pulse impinging on a metal nano-layer, non-oscillatory wake-fields appear with a definite sign. The magnitude of these wake-fields is proportional with the incoming field strength, and a sign of them is governed by the cosine of the carrier-envelope phase difference of the incoming pulse. At relativistic laser intensities the target is considered as a plasma layer in vacuum, produced from a thin foil by a pre-pulse, which is followed by the main high-intensity laser pulse. The nonlinearities stemming from the relativistic kinematics of the surface current density (representing the plasma electrons) lead to the appearance of higher-harmonics in the scattered spectra. In general, the harmonic peaks are down-shited due to the presence of an intensity-dependent factor. Certain regions of these spectra are very sensitive to the variation of the carrier-envelope phase difference. The spectra has a long tail where the heigths of the peaks vary practically within one order of magnitude forming a quasi-continuum. By Fourier synthetising the components from this plateau region attosecond pulses have been obtained.