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Smith A.V.,AS Photonics LLC | Smith J.J.,AS Photonics LLC
IEEE Journal on Selected Topics in Quantum Electronics | Year: 2014

We offer an overview of the concepts, numerical methods, and applications of our model of stimulated thermal Rayleigh scattering in large mode area fiber amplifiers. This overview is intended to consolidate and summarize our studies of modal instability thresholds and how to maximize them. Several movies of thermal grating evolution and modal power evolution are presented for the first time. © 1995-2012 IEEE. Source


Smith A.V.,AS Photonics LLC | Smith J.J.,AS Photonics LLC
Optics Express | Year: 2012

Using numerical simulations of thermally induced mode coupling we show how the instability threshold can be substantially reduced if the pump or injected signal is modulated in the kHz range. We also show how the mode coupling gain varies with the frequency offset of the parasitic mode. We model thresholds when the source of detuned light is quantum background, amplitude modulation of the pump power, and amplitude modulation of the signal seed. We suggest several key experimental and modeling tests of our model. © 2012 Optical Society of America. Source


Smith A.V.,AS Photonics LLC | Smith J.J.,AS Photonics LLC
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

We show by detailed numerical modeling that stimulated thermal Rayleigh scattering can account for the modal instability observed in high power fiber amplifiers. Our model illustrates how the instability threshold power can be maximized by eliminating amplitude and phase modulation of the signal seed light and the pump light and by careful injection of the signal seed light. We also illustrate the influence of photodarkening and mode specific loss. © 2013 Copyright SPIE. Source


Smith A.V.,AS Photonics LLC | Smith J.J.,AS Photonics LLC
Optics Express | Year: 2013

We present a detailed description of the methods used in our model of mode instability in high-power, rare earth-doped, large-mode-area fiber amplifiers. Our model assumes steady-periodic behavior, so it is appropriate to operation after turn on transients have dissipated. It can be adapted to transient cases as well. We describe our algorithm, which includes propagation of the signal field by fast-Fourier transforms, steadystate solutions of the laser gain equations, and two methods of solving the time-dependent heat equation: alternating-direction-implicit integration, and the Green's function method for steady-periodic heating. © 2013 Optical Society of America. Source


Smith A.V.,AS Photonics LLC | Smith J.J.,AS Photonics LLC
Optics Express | Year: 2011

For powers exceeding a sharp threshold in the vicinity of several hundred watts the beam quality from some narrow bandwidth fiber amplifiers is severely degraded. We show that this can be caused by transverse thermal gradients induced by the amplification process. © 2011 Optical Society of America. Source

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