Experimental demonstration of coherent beam combining over a 7 km propagation path

Weyrauch, Thomas; Vorontsov, Mikhail A.; Carhart, Gary W.; Beresnev, L. A.; Rostov, Andrey P.; Polnau, Ernst; Liu, Jony Jiang

doi:10.1364/ol.36.004455

Cited by 145 publications

(49 citation statements)

References 8 publications

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“…Still, most prior applications were for continuous wave fronts, whereas here we deal with sparse ones. These optimization algorithms also have been successfully used as the control algorithms for coherent beam combining of fiber arrays [16][17][18][19]. The convergence rate of the SA algorithm was compared to other optimization algorithms by a number of authors [20,21] and these papers show that the GA is the slowest algorithm, while SA and SPGD have comparable convergence rates.…”

Section: Previous Optimization Approaches For Adaptive Optics Sysmentioning

confidence: 99%

Phasing a segmented telescope

et al. 2015

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A crucial part of segmented or multiple-aperture systems is control of the optical path difference between the segments or subapertures. In order to achieve optimal performance we have to phase subapertures to within a fraction of the wavelength, and this requires high accuracy of positioning for each subaperture. We present simulations and hardware realization of a simulated annealing algorithm in an active optical system with sparse segments. In order to align the optical system we applied the optimization algorithm to the image itself. The main advantage of this method over traditional correction methods is that wave-front-sensing hardware and software are no longer required, making the optical and mechanical system much simpler. The results of simulations and laboratory experiments demonstrate the ability of this optimization algorithm to correct both piston and tip-tilt errors.

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Section: Previous Optimization Approaches For Adaptive Optics Sysmentioning

confidence: 99%

Phasing a segmented telescope

et al. 2015

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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%

“…Coherent combining has proven to be effective in situations with very low-power lasers and weak turbulence [4]. However, these conditions are not applicable for DE systems which require high-power lasers and must be effective in conditions of moderate and strong atmospheric turbulence.…”

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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“…In the presence of a point source target, the N number of beamlets within a tiled aperture can be phased, in piston, using electro-optic modulators, a high-speed optical detector, and high-bandwidth controls [1][2][3][4][5][6][7][8][9][10]. This paper uses a series of simulated wave optics experiments to explore the performance limitations of ideal piston phase compensation [11].…”

Section: Introductionmentioning

confidence: 99%

Piston phase compensation of tiled apertures in the presence of turbulence and thermal blooming

Spencer

Thornton

Hyde

et al. 2014

2014 IEEE Aerospace Conference

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With current phasing technolog y , the individual beam lets within a tiled aperture can be phased in piston to coherentl y combine at the target. In practice, this piston phasing of the optical beamlet trains is accomplished using a point-source target. The reflections from the point-source target act as an idealized beacon, which propagate from the target to the tiled aperture through aberrations induced within the optical beamlet trains. Thus, an ideal reference is achieved to perform piston phase compensation b y exploiting high bandwidth phase loops. This paper investigates piston phase compensation of tiled apertures in the presence of horizontal path turbulence and thermal blooming b y using wave-optics simulations. To represent different arra y fill factors in the source plane, both seven and 19 element hexagonal close packed tiled apertures are used in the simulations along with both Gaussian and flat-top outgoing beam lets. Performance is evaluated b y calculating peak Strehl ratio and power in the bucket in the target plane for all simulation setups and averaging these performance metrics for multiple realizations of turbulence and thermal blooming. The performance metrics are plotted as a function of the Fried coherence diameter, the log-amplitude variance, and the distortion number for comparison purposes. In general, the results show that piston phase compensation does not perform well when the subaperture diameter is greater than the coherence diameter and when the distortion number is greater than 21rad. These results are intuitive; however, the trends are often nonlinear with distinct as y mptotes. With this said, the results presented in this paper should help future conceptual designs.

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Experimental demonstration of coherent beam combining over a 7 km propagation path

Cited by 145 publications

References 8 publications

Phasing a segmented telescope

Phasing a segmented telescope

Atmospheric Propagation and Combining of High-Power Lasers

Piston phase compensation of tiled apertures in the presence of turbulence and thermal blooming

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