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The four-wave mixing process during a single-color femtosecond filamentation in the molecular gas is observed experimentally. The role of the seed is represented by the selfshifted to infrared region Raman bullet and the new blue-shifted component burns up as a result of the interaction between the Raman bullet and the reservoir radiation. The blueshifted component propagates along the beam axis. The theoretical analysis of the four-wave mixing process synchronism shows that the on-axis forward propagation of the blueshifted component occurs when the plasma concentration is higher than a certain threshold (3.3 × 10 16 cm −3 at the fundamental wavelength of 800 nm).

High-intensity (∼1 TW/cm2 and higher) region formed in the propagation of ∼60 GW, 90 fs Ti:Sapphire laser pulse on a ∼100 m path in air spans for several tens of meters and includes a plasma filament and a postfilament light channel. The intensity in this extended region is high enough to generate an infrared supercontinuum wing and to initiate laser-induced discharge in the gap between the electrodes. In the experiment and simulations, we delay the high-intensity region along the propagation direction by inserting metal-wire meshes with square cells at the laser system output. We identify the presence of a high-intensity region from the clean-spatial-mode distributions, appearance of the infrared supercontinuum wing, and occurrence of the laser-induced discharge. In the case of free propagation (without any meshes), the onset of the high-intensity zone is at 40–52 m from the laser system output with ∼30 m extension. Insertion of the mesh with 3 mm cells delays the beginning of the high-intensity region to 49–68 m with the same ∼30 m extension. A decrease in the cell size to 1 mm leads to both delay and shrinking of the high-intensity zone to 71–73 m and 6 m, respectively. Three-dimensional simulations in space confirm the mesh-induced delay of the high-intensity zone as the cell size decreases.