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Demonstration of Long-Lived High-Power Optical Waveguides in Air

N. Jhajj, E. W. Rosenthal, R. Birnbaum, J. K. Wahlstrand, and H. M. Milchberg
Phys. Rev. X 4, 011027 – Published 26 February 2014
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Abstract

We demonstrate that femtosecond filaments can set up an extended and robust thermal waveguide structure in air with a lifetime of several milliseconds, making possible the very-long-range guiding and distant projection of high-energy laser pulses and high-average power beams. As a proof of principle, we demonstrate guiding of 110-mJ, 7-ns, 532-nm pulses with 90% throughput over 15 Rayleigh lengths in a 70-cm-long air waveguide generated by the long time-scale thermal relaxation of an array of femtosecond filaments. The guided pulse was limited only by our available laser energy. In general, these waveguides should be robust against the effects of thermal blooming of extremely high-average-power laser beams.

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  • Received 7 November 2013

DOI:https://doi.org/10.1103/PhysRevX.4.011027

This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Published by the American Physical Society

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A Waveguide Made of Hot Air

Published 26 February 2014

The thermal wake left in air by a bundle of intense laser pulses can act as a channel for sending subsequent laser light over long distances.

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Authors & Affiliations

N. Jhajj, E. W. Rosenthal, R. Birnbaum, J. K. Wahlstrand, and H. M. Milchberg*

  • Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742, USA

  • *Corresponding author. milch@umd.edu

Popular Summary

An intense ultrashort pulse of laser light traveling in a gas can distort the atoms or molecules in its vicinity, creating an effective self-lens that moves with the pulse at the speed of light and causes it to focus and partially ionize the gas. The ionized gas causes defocusing, and the interplay between the self-lens focusing and plasma defocusing results in a spatially tight region of high laser intensity, called a filament, that can propagate for kilometer-scale distances—well beyond the so-called Rayleigh range over which diffractive beam spreading typically reduces a beam’s intensity. However, instabilities limit the pulse energy a single, high-intensity filament can carry to about 0.001 joule. As a result, even when a series of filament pulses are generated at a repetition rate of thousands of pulses per second, they can deliver, at most, an average power of several watts.

Here, we demonstrate an approach to guiding pulses with much higher average power. We launch an array of four femtosecond filaments arranged in a square configuration. The filaments act as a distributed array of impulsive heat sources in the air, driving gas hydrodynamics. The relatively higher density of air in the thermal wake of the array’s center acts as a waveguide that can support the propagation of a subsequent high-power pulse of light for up to several milliseconds. As a proof of principle, we show that the thermal waveguide allows us to transmit a nanosecond laser pulse that carries about 100 times more energy than a typical single filament over many Rayleigh ranges.

Our air waveguide can also resist the effects of thermal blooming, in which high-average power beams tend to defocus and spread because they heat the air in their path. This will enable applications that require very high-average power beams to be guided over long distances. One potential application of our air waveguide is the remote detection of harmful chemicals or explosives, in which the waveguide would function as a light pipe that collects remote optical signals.

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Vol. 4, Iss. 1 — January - March 2014

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It is not necessary to obtain permission to reuse this article or its components as it is available under the terms of the Creative Commons Attribution 3.0 License. This license permits unrestricted use, distribution, and reproduction in any medium, provided attribution to the author(s) and the published article's title, journal citation, and DOI are maintained. Please note that some figures may have been included with permission from other third parties. It is your responsibility to obtain the proper permission from the rights holder directly for these figures.

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