Propagation of Femtosecond Radiation in Air and the Formation of Subdiffraction Divergence Beams

The results of complex studies of propagation of a wide (5 cm diameter) femtosecond laser beam generated by a titanium-sapphire laser (wavelength 0.78 $\mu\mathrm{m}$, peak pulse power 1 TW) are discussed. Both the location of the domain where filamentation occurs and its structure were changed by introducing controlled distortions of the wave phase at the expense of a multi-element deformable mirror. The advantages of using this mirror (compared to spherical lenses and mirrors) for laser radiation focusing are demonstrated. Focusing femtosecond laser radiation with a bimorph deformable mirror allows the filamentation region to be moved along the entire path and does not (significantly) decrease its length. The spatial position of the high-intensity light channels formed in the laser beam can be configured. The existence of a regime of radiation propagation without ionization is shown, in which ordered sets of high-intensity (1011–1012 W/cm2) weakly diverging (less than 0.01 mrad) light channels are formed. These channels are characterized by a millimeter diameter and large spatial extent (over 100 m).