Fiber laser beam combining and power scaling progress: Air Force Research Laboratory Laser Division

Wagner, Torrey

doi:10.1117/12.912154

Cited by 18 publications

(5 citation statements)

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“…8 Phased array configurations of laser fiber amplifiers have been demonstrated in the laboratory. 9,10,11,12,13 A phased array design requires a control scheme to ensure that individual beams are in phase in the far-field. In a standard approach, heterodyning systems employ phase feedback based on sampling and comparing the output phase of each emitter to a global reference phase, such as produced by a master oscillator.…”

Section: Laser Phased Array Conceptmentioning

confidence: 99%

Local phase control for a planar array of fiber laser amplifiers

Steffanic¹,

Johannes²,

Sison³

et al. 2015

SPIE Proceedings

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Arrays of phase-locked lasers have been developed for numerous directed-energy applications. Phased-array designs are capable of producing higher beam intensity than similar sized multi-beam emitters, and also allow beam steering and beam profile manipulation. In phased-array designs, individual emitter phases must be controllable, based on suitable feedback. Most current control schemes sample individual emitter phases, such as with an array-wide beam splitter, and compare to a master phase reference. Reliance on a global beam splitter limits scalability to larger array sizes due to lack of design modularity. This paper describes a conceptual design and control scheme that relies only on feedback from the array structure itself. A modular and scalable geometry is based on individual hexagonal frames for each emitter; each frame cell consists of a conventional lens mounted in front of the fiber tip. A rigid phase tap structure physically connects two adjacent emitter frame cells. A target sensor is mounted on top of the phase tap, representing the local alignment datum. Optical sensors measure the relative position of the phase tap and target sensor. The tap senses the exit phase of both emitters relative to the target normal plane, providing information to the phase controller for each emitter. As elements are added to the array, relative local position data between adjacent phase taps allows accurate prediction of the relative global position of emitters across the array, providing additional constraints to the phase controllers. The approach is scalable for target distance and number of emitters without loss of control.

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Section: Laser Phased Array Conceptmentioning

confidence: 99%

Local phase control for a planar array of fiber laser amplifiers

Steffanic¹,

Johannes²,

Sison³

et al. 2015

SPIE Proceedings

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“…A class of phase locking methods that similar to OHD also utilize heterodyne beats are synchronous multidither approaches and variants thereof [17,18,[23][24][25][26][27]. The application of multidither methods for phasing arrays of high-power lasers was fully conceived by the 1970s in the context of atmospheric propagation [23], although the lack of high-speed modulators and sensing electronics severely limited the performance.…”

Section: Synchronous Multidithermentioning

confidence: 99%

“…The main disadvantage of multidither is its relative electronic complexity and cost, which has at present limited demonstrations to 32 channels [17] despite clear potential for multihundred channel scalability based on signal-to-noise considerations [18]. Minimization of the beat signals in the combined beams corresponds to the condition where all beams are in-phase.…”

Section: Synchronous Multidithermentioning

confidence: 99%

Engineering of Coherently Combined, High‐Power Laser Systems

Goodno

Rothenberg

2013

Coherent Laser Beam Combining

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In recent years, much effort has been expended toward scaling electric lasers to CW power levels on the order of 100 kW or greater [1]. The key challenge in such scaling is maintaining near-diffraction-limited (DL) beam quality (BQ) to enable tight focusing onto a distant target. Despite the maturation of scalable, diode-pumped laser amplifier technologies such as zigzag slabs [2] or fibers [3], thermal effects or optical nonlinearities currently limit near-DL output from single lasers to an order of magnitude lower power, around 10 kW.Actively phase-locked coherent beam combination (CBC) of N laser amplifiers seeded by a common master oscillator (MO) represents an engineerable approach toward scaling laser brightness B (loosely defined here as B $ power/BQ 2 ) beyond the limits of the underlying single-element laser technology. Ideally, the combined output behaves as if it were a single beam, and B is thereby increased by a factor of N over an unphased array or by a factor of N 2 over any individual laser [4].A compelling architectural advantage of CBC systems in comparison to singleaperture lasers of comparable power is the graceful degradation in response to failure of any gain element. This feature can be elucidated from the scaling of B $ N 2 , so the relative rate of change in brightness as individual lasers fail is 1/B(dB/dN) ¼ 2/N. Hence, for large arrays, the drop in brightness is gradual. For example, failure of 1 out of N ¼ 100 lasers would still allow a CBC system to continue operating at 98% of its original brightness.Active CBC with servo-based phase locking can be straightforwardly engineered for very high channel counts and for very high-power laser gain elements. Recently, Northrop Grumman Aerospace Systems adopted an actively phaselocked approach to combine seven 15 kW Nd:YAG slab amplifier chains to demonstrate the world's first 100 kW electric laser with record-setting brightness [5]. As of this writing, work is underway to extend this technology to achieve similar power levels in a CBC array of fiber lasers with improved BQ and efficiency as well as reduced size and weight [6,7].

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“…The LOCSET technique can be operated in a self-referenced or self-synchronous context [282,283]. Various research has been conducted on CBC laser systems based on the LOCSET technique [169,175,181,186,187,192,278,[284][285][286].…”

mentioning

confidence: 99%

Towards Ultimate High-Power Scaling: Coherent Beam Combining of Fiber Lasers

2021

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Fiber laser technology has been demonstrated as a versatile and reliable approach to laser source manufacturing with a wide range of applicability in various fields ranging from science to industry. The power/energy scaling of single-fiber laser systems has faced several fundamental limitations. To overcome them and to boost the power/energy level even further, combining the output powers of multiple lasers has become the primary approach. Among various combining techniques, the coherent beam combining of fiber amplification channels is the most promising approach, instrumenting ultra-high-power/energy lasers with near-diffraction-limited beam quality. This paper provides a comprehensive review of the progress of coherent beam combining for both continuous-wave and ultrafast fiber lasers. The concept of coherent beam combining from basic notions to specific details of methods, requirements, and challenges is discussed, along with reporting some practical architectures for both continuous and ultrafast fiber lasers.

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Fiber laser beam combining and power scaling progress: Air Force Research Laboratory Laser Division

Cited by 18 publications

References 0 publications

Local phase control for a planar array of fiber laser amplifiers

Local phase control for a planar array of fiber laser amplifiers

Engineering of Coherently Combined, High‐Power Laser Systems

Towards Ultimate High-Power Scaling: Coherent Beam Combining of Fiber Lasers

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