Externally refuelled optical filaments

Journal name:
Nature Photonics
Year published:
Published online


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


  1. A dressed filament considerably protracts the longevity of an optical filament.
    Figure 1: A dressed filament considerably protracts the longevity of an optical filament.

    a, A pulsed Gaussian beam (shown in the top inset) with sufficient energy will undergo self-focusing collapse and form a filament that propagates a distance L1. b, If, however, this same beam is appropriately dressed with a convergent annular beam (bottom inset), the filament range can be extended by an additional distance L2. Yellow arrows in the inset represent the transverse Poynting vector for the energy influx into the filament core.

  2. Experimental investigation of dressed optical filaments.
    Figure 2: Experimental investigation of dressed optical filaments.

    a, Experimental set-up. The input beam is unevenly divided into two parts. The lower-energy portion is focused by a convergent lens with a focal length of 2 m and produces a short plasma filament in air. The higher-energy beam is passed through a shallow axicon lens and assumes the role of the dressing beam. Plasma generation in air is quantified using a capacitive plasma probe. b, Intensity profile of the primary and dressing beams together, observed just before the interaction zone. c, Experimental demonstration of an extended filament when the primary beam carries an energy of 0.87 mJ and the accompanying dressing beam 3.50 mJ. In this arrangement, the light string propagates for 220 cm, which corresponds to an 11-fold improvement over the unaided filament. Data points were obtained by averaging over 100 laser shots, and error bars represent the corresponding standard deviation. d, Plasma density as obtained from numerical simulations for the three cases in c. This also corroborates an 11-fold extension of the filamentation process with the aid of a dressing beam.

  3. Plasma density generated by the application of a Bessel beam for different values of laser energy.
    Figure 3: Plasma density generated by the application of a Bessel beam for different values of laser energy.

    The length of the plasma filament in this case falls short of that achieved in the dressed filament scenario (shown in Fig. 2c), even when the energy in the Bessel beam is about twice the energy in the Gaussian and dressing beams combined. Data points were obtained by averaging the plasma densities of 100 pulses. The resulting error bars represent the standard deviation of these measurements.

  4. Dressed optical filaments in long-range settings.
    Figure 4: Dressed optical filaments in long-range settings.

    a, Numerical simulation of the peak on-axis intensity for a collimated Gaussian beam starting with 2 mm FWHM and 2 mJ of energy. The string decays after ~3 m. b, Maximum on-axis intensity when a dressing beam with 26 mJ of energy propagates alone. Even with this large amount of energy, a filament never forms because the dress maintains a low intensity throughout propagation and only refuels the pre-existing filament. c, On-axis intensity when the central beam in a is aided by the same co-propagating dressing wave in b. Here, the dressed filament propagates over 45 m, a 15-fold improvement over the previous result. d, Propagation dynamics when all 28 mJ of energy are packed in a Gaussian beam that propagates alone. High on-axis intensity is maintained for only 13 m. eh, Intensity cross-sections as a function of propagation distance corresponding to ad, respectively. In each case, the propagation varying FWHM of the central beam is indicated by a pair of yellow lines. In f, the intensity of the dressing beam propagating alone is considerably lower during propagation. In g, the filament maintains an intensity FWHM of ~100 µm over a distance of 45 m (Supplementary Section 9).


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Author information

  1. These authors contributed equally to this work

    • Maik Scheller &
    • Matthew S. Mills


  1. The College of Optical Sciences, The University of Arizona, 1630 East University Boulevard, Tucson, Arizona 85721, USA

    • Maik Scheller,
    • Weibo Cheng,
    • Jerome V. Moloney,
    • Miroslav Kolesik &
    • Pavel Polynkin
  2. CREOL, College of Optics and Photonics, University of Central Florida, PO Box 162700, Orlando, Florida 32816-2700, USA

    • Matthew S. Mills,
    • Mohammad-Ali Miri &
    • Demetrios N. Christodoulides
  3. Department of Physics, Constantine the Philosopher University, Trieda A. Hlinku 1, 94974 Nitra, Slovakia

    • Miroslav Kolesik


M.S.M., M.K. and D.N.C. suggested the idea of dressed filaments. M.S.M., M.-A.M. and D.N.C. produced the manuscript, figures and accompanying Supplementary Information. M.S.M. explored the theoretical aspects of the paper and simulated the process using M.K.'s code. M.S., W.C., J.V.M. and P.P. carried out the experiments reported in this study.

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