Beam quality and noise properties of coherently combined ytterbium doped single frequency fiber amplifiers

Tünnermann, Henrik; Pöld, J.; Neumann, Jörg; Kracht, Dietmar; Willke, B.; Weßels, P.

doi:10.1364/oe.19.019600

Cited by 27 publications

(9 citation statements)

References 21 publications

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“…When stabilizing the phase using the ytterbium amplifiers, the unity gain frequency was 1 kHz, so this region is not in the control loop bandwidth. Overall, the noise is mostly limited by the single amplifier noise, which was also the case in our free space system [4]. This is quite surprising considering the pump stabilization scheme converts phase noise to power noise.…”

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confidence: 60%

“…Its scalability beyond the usual single amplifier limits due to nonlinearities or thermal effects enables kilowatt class single frequency sources [1] and generation of high energy pulses [2,3]. Because beam quality and noise properties of a single amplifier can be preserved, it is a promising concept for the laser source for third generation gravitational wave detectors [4]. Nevertheless, a major drawback of these systems is the increased complexity due to the multiple paths, required control loops, and actuators.…”

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confidence: 99%

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All-fiber coherent beam combining with phase stabilization via differential pump power control

et al. 2012

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Coherent beam combining enables power scaling beyond the limits of single amplifiers. Therefore, improving the performance and simplicity of coherent combination techniques is of great interest for many high power applications. Here, we show all-fiber coherent beam combining of two ytterbium doped amplifiers with and without a dedicated phase actuator and a total output power up to 25 W. Instead of a dedicated phase actuator, we directly controlled the two ytterbium amplifiers to also stabilize their relative phase. We compared the performance of this method with phase stabilization using two piezo driven fiber stretchers. In both cases, power noise was dominated by the single amplifier.

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confidence: 60%

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confidence: 99%

All-fiber coherent beam combining with phase stabilization via differential pump power control

et al. 2012

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“…(1.4) arise purely from uncorrelated aberrations between beams, the CBC process can be seen to serve as an effective "coherent filter." Due to this coherent filtering effect, CBC appears a promising technology for applications requiring extremely high-quality, high-power beams, such as interferometers for gravity wave detection [15], or resonant cavity-enhanced high-harmonic generation [16]. The physical intuition is that uncorrelated aberrations captured by the terms in Eq.…”

Section: Coherent Beam Combining System Requirementsmentioning

confidence: 99%

Engineering of Coherently Combined, High‐Power Laser Systems

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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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“…There is no solution for this problem known, yet. Thus, alternative power scaling options such as coherent beam combining may have to be implemented in order to overcome these limitations [4].…”

Section: Amplifier Setup and Power Scalingmentioning

confidence: 99%