Plasma channels produced in air through femtosecond laser filamentation1, 2, 3, 4 hold great promise for a number of applications, including remote sensing5, attosecond physics6, 7 and spectroscopy8, channelling microwaves9, 10, 11, 12 and lightning protection13. In such settings, extended filaments are desirable, yet their longitudinal span is limited by dissipative processes. Although various techniques aiming to prolong this process have been explored, the substantial extension of optical filaments remains a challenge14, 15, 16, 17, 18, 19, 20, 21. Here, we experimentally demonstrate that the natural range of a plasma column can be enhanced by at least an order of magnitude when the filament is prudently accompanied by an auxiliary beam. In this arrangement, the secondary low-intensity ‘dressing’ beam propagates linearly and acts as a distributed energy reservoir22, continuously refuelling the optical filament. Our approach offers an efficient and viable route towards the generation of extended light strings in air without inducing premature wave collapse or an undesirable beam break-up into multiple filaments2.
At a glance
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