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Non-linear cumulative self-organization dynamics of femtosecond laser-induced surface relief ripples was for the first time experimentally revealed on a silicon surface as their primary appearance, degradation and revival, reflecting ultrafast non-linear dynamics of corresponding optical interference surface patterns. Such dynamics were revealed by electrodynamic modeling to be directly driven by related instantaneous surface optical patterns, which are sensitive not only to cumulative ripple deepening (steady-state feedback factor), but to laser-induced instantaneous variation of surface dielectric function, providing either positive or negative fluence-dependent optical feedbacks.

Filamentation of focused UV and IR femtosecond laser pulses and plasma channel formation governed by variable wavefront distortions was experimentally and numerically studied. A deformable mirror was used to control the plasma channel length by introducing a spherical aberration into the initial transverse spatial distribution of a femtosecond laser pulse. An at least double increase of the plasma channel length was observed with increasing deformation of the mirror. Numerical calculations show that the hat-like phase shape of the aberration ensures that the energy of the initial laser pulse remains confined for a longer distance within the limited transverse size of the filament.

We report the results of theoretical and experimental study of the characteristic time for three-body attachment of electrons produced by 100 fs UV laser pulse in the atmosphere air in the external DC electric field ranged from 0.2 to 10 kV/cm.

One-dimensional transverse (perpendicular to the laser polarization) gratings with periods Λ ≈ 50–60 nm were observed on a titanium surface within 150 nm wide, micrometer-long regular surface modification longitudinal stripes fabricated by multiple 744 nm Ti:sapphire femtosecond laser shots, occurring at a repetition rate of 10 Hz. In the center of the surface laser spot these stripes are oriented strictly perpendicular to the laser polarization, in accordance with the plasmon-polaritonic model, and appear as ablative longitudinal trenches centered along the main stripe axes, which are precursors of longitudinal common ripples with a 500 nm period. At the low-fluence periphery of the laser spot, the stripes appear not as ablative longitudinal trenches, but as linear arrays of sub-ablative transverse nanoripples with periods down to 50 nm. The appearance of such superfine transverse nanoripples is related to incomplete spallation of the laser–molten surface layer, periodically modulated at the nanoscale through coherent sub-surface cavitation.

Femtosecond laser modification of titanium surfaces was performed to produce microstructured hydrophilic and biocompatible surface layers. Biocompatible nano/microcoatings were prepared for the first time by dry femtosecond laser imprinting of hydroxylapatite nano/micropowder onto VT6 titanium surfaces. In these experiments HAP was first deposited onto the titanium surfaces and then softly imprinted by multiple femtosecond laser pulses into the laser-melted surface metal layer. The surface relief was modified at the nano- and microscales depending on the incident laser fluence and sample scanning speed. Wetting tests demonstrated that the wetting properties of the pristine Ti surface can be tuned through its laser modification in both the hydrophobic and hydrophilic directions.

Non-self-sustained electric discharge and electric breakdown were triggered and guided by a train of picosecond ultraviolet (UV) pulses overlapped with a long free-running UV pulse of a hybrid Ti:Sapphire-KrF laser facility. Photocurrent sustained by this train is two orders of magnitude higher, and electric breakdown distance is twice longer than those for the discharge triggered by the long UV pulse only.