Incoherent Combining and Atmospheric Propagation of High-Power Fiber Lasers for Directed-Energy Applications

Sprangle, P.; Ting, A.; Peñano, Joseph; Fischer, Richard; Hafizi, B.

doi:10.1109/jqe.2008.2002501

Cited by 128 publications

(56 citation statements)

References 6 publications

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“…The first vibration overtone of the O-H bond in water has an absorption wavelength of 1.92-1.94 mm, which can be used for laser surgery 5 . The atmospheric transmission window also includes the 2-mm region, unlocking the way to energy delivery 6 or free-space communications 7 . Recently, the potential of hollow-core photonic bandgap fibers 8 combined with thulium-doped fiber (TDF) amplifiers 9 for fiber optical telecommunication in the 1910-2020 nm band was reported.…”

Section: Introductionmentioning

confidence: 99%

Isolator-free unidirectional thulium-doped fiber laser

Kharitonov

Brès

2015

Light Sci Appl

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We report the first demonstration of a unidirectional, isolator-free 2-mm thulium-doped fiber (TDF) laser, relying on the properties of the theta cavity (ring resonator with S-shaped feedback). The core pumped theta cavity TDF laser provides sub-Watt output power with a slope efficiency of 25%, a 2 dB flat tuning range of 1900-2050 nm, and a linewidth of 0.2 nm, and achieves the extinction ratio of 18-25 dB (depending on the feedback value) between the favored and suppressed lasing directions. It is shown that these characteristics are competitive with, if not superior to, those of conventional ring cavities. The simulation results of the linear and Kerr-nonlinear theta cavities are also presented, explaining certain unexpected features of the laser behavior and establishing the importance of the doped fiber nonlinearity on the spectral shaping of the emitted signal.

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Section: Introductionmentioning

confidence: 99%

Isolator-free unidirectional thulium-doped fiber laser

Kharitonov

Brès

2015

Light Sci Appl

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“…With either approach, he says, "when you're propagating over long ranges through atmospheric turbulence, you get approximately the same power on the target". In 2009, his group confirmed this theory by using mirrors to combine 4 fibre-laser beams into a 5-centimetre spot on a target more than 3 kilometres away 3 . Building on Sprangle's work, the US Office of Naval Research has developed the 30-kW LaWS, which incoherently combines six commercial fibre-lasers.…”

Section: Strength In Numbersmentioning

confidence: 97%

Military technology: Laser weapons get real

Extance¹

2015

Nature

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“…The combined beam is then propagated many kilometers through a turbulent atmosphere. Recently, much effort has been expended in coherent beam combining [2][3][4][5][6][7]. Coherent beam combining refers to matching the phases of multiple lasers either in the transmitter plane [2,3] or the target plane [4].…”

Section: Introductionmentioning

confidence: 99%

Atmospheric Propagation and Combining of High-Power Lasers

Nelson¹,

Sprangle²,

Davis³

2015

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Standard Form 298 (Rev. 8-98)Prescribed by ANSI Std. Z39.18Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing this collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden to Department of Defense, Washington Headquarters Services, Directorate for Information In this paper we analyze the beam combining and atmospheric propagation of high-power lasers for directed-energy (DE) applications. The large linewidths inherent in high-power fiber, and to a lesser extent, slab lasers cause random phase and intensity fluctuations occurring on sub-nanosecond time scales. To coherently combine these high-power lasers would involve instruments capable of precise phase control and operating at rates greater than ~10 GHz. To the best of our knowledge, this technology does not currently exist. This presents a challenging problem when attempting to phase-lock high-power lasers, which is not encountered when phase-locking low-power lasers, for example mW power levels. Regardless, we demonstrate that even if instruments are developed that can precisely control the phase of high-power lasers; coherent combining is problematic for DE applications. The dephasing effects of atmospheric turbulence typically encountered in DE applications will degrade the coherent properties of the beam before it reaches the target. Through simulations, we find that coherent beam combining in moderate turbulence and multi-km propagation distances has little advantage over incoherent combining. Additionally, in strong turbulence and multi-km propagation ranges, we find nearly indistinguishable intensity profiles and virtually no difference in the energy on the target between coherently and incoherently combined laser beams. Consequently, we find that coherent beam combining at the transmitter plane is ineffective under typical atmospheric conditions. AbstractIn this paper we analyze the beam combining and atmospheric propagation of high-power lasers for directed-energy (DE) applications. The large linewidths inherent in high-power fiber, and to a lesser extent, slab lasers cause random phase and intensity fluctuations occurring on subnanosecond time scales. To coherently combine these high-power lasers would involve instruments capable of precise phase control and operating at rates greater than ~10 GHz. To the best of our knowledge, this technology does not currently exist. This presents a challenging problem when attempting to phase-lock high-power lasers, which is not encountered when phaselocking low-power lasers, for example mW power levels. Regardless, we demonstrate that even if instruments are developed that can precisely control the phase of high-power lasers; coherent combining is problematic for DE applications. The dephasing ...

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Incoherent Combining and Atmospheric Propagation of High-Power Fiber Lasers for Directed-Energy Applications

Cited by 128 publications

References 6 publications

Isolator-free unidirectional thulium-doped fiber laser

Isolator-free unidirectional thulium-doped fiber laser

Military technology: Laser weapons get real

Atmospheric Propagation and Combining of High-Power Lasers

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