2,501 research outputs found
Increased mode instability thresholds of fiber amplifiers by gain saturation
We show by numerical modeling that saturation of the population inversion
reduces the stimulated thermal Rayleigh gain relative to the laser gain in
large mode area fiber amplifiers. We show how to exploit this effect to raise
mode instability thresholds by a substantial factor. We also demonstrate that
when suppression of stimulated Brillouin scattering and the population
saturation effect are both taken into account, counter-pumped amplifiers have
higher mode instability thresholds than co-pumped amplifiers for fully
Yb doped cores, and confined doping can further raise the thresholds.Comment: 13 pages, 8 figure
Frequency dependence of mode coupling gain in Yb doped fiber amplifiers due to stimulated thermal Rayleigh scattering
Using a numerical model we study the frequency dependence of mode coupling
gain due to stimulated thermal Rayleigh scattering in step index, Yb doped,
fiber amplifiers. The frequency at the gain peak is shown to vary with core
size, doping size, population saturation, thermal lensing, fiber coiling,
direction of pumping, photodarkening, and pump noise spectra. The predicted
frequencies are compared with measured values whenever possible.Comment: 13 pages, 12 figure
Maximizing the mode instability threshold of a fiber amplifier
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 and
the pump, and by careful launch of the signal seed. We also illustrate the
influence of photodarkening and mode specific loss on the threshold.Comment: 7 pages, 7 figure
Modeled fiber amplifier performance near the mode instability threshold
We numerically model fiber amplifier performance near and slightly above the
mode instability threshold. These results are compared with recently published
experimental work. Using weakly amplitude modulated pump light we obtain
qualitative agreement with the measured instability thresholds, mode switching
ranges, pixel power modulations, and modal amplitude modulations.Comment: 8 pages, 5 figure
Spontaneous Rayleigh seeding of stimulated Rayleigh scattering in high power fiber amplifiers
We estimate the Stokes wave starting power for stimulated thermal Rayleigh
scattering (STRS) produced by thermal fluctuations in the fiber core that
transiently alter the refractive index profile in the core. A transverse
temperature gradient creates a transverse refractive index gradient via the
thermo optic effect, and if the fluctuation frequency lies in the STRS gain
band, it can couple light from mode LP to LP to seed STRS. This
spontaneous Rayleigh seed may be stronger than the quantum background and may
affect the mode instability thresholds of fiber amplifiers. This new seed
estimate can be incorporated in STRS models to improve threshold calculations.Comment: 7 pages, 1 figure. Accepted for publication by IEEE Photonics Journa
Steady-periodic method for modeling mode instability in fiber amplifiers
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, steady-state 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.Comment: 19 pages, 2 figure
Influence of signal bandwidth on mode instability threshold of fiber amplifiers
We show how signal linewidth affects the gain of stimulated thermal Rayleigh
scattering (STRS) which is responsible for mode instability in fiber
amplifiers. The gain is reduced if the coherence time of the signal is less
than the group velocity induced walk off between modes LP and LP.
We derive equations for short pulses, linear chirps, and general periodic
cases.Comment: 3 figure
When Ideal-based Zero-divisor Graphs are Complemented or Uniquely Complemented
Let be a commutative ring with nonzero identity and a proper ideal of
. The {\it ideal-based zero-divisor graph} of with respect to the ideal
, denoted by , is the graph on vertices for some , where distinct vertices and
are adjacent if and only if . In this paper, we classify when an
ideal-based zero-divisor graph of a commutative ring is complemented or
uniquely complemented.Comment: 6 Page
Mode instability thresholds for Tm-doped fiber amplifiers pumped at 790 nm
We use a detailed numerical model of stimulated thermal Rayleigh scattering
to compute mode instability thresholds in Tm-doped fiber amplifiers. The
fiber amplifies 2040 nm light using a 790 nm pump. The cross-relaxation process
is strong, permitting power efficiencies of 60%. The predicted instability
thresholds are compared with those in similar Yb-doped fiber amplifiers
with 976 nm pump and 1060 nm signal, and are found to be higher, even though
the heat load is much higher in Tm-doped amplifiers. The higher threshold in
the Tm-doped fiber is attributed to its longer signal wavelength, and to
stronger gain saturation, due in part to cross-relaxation heating.Comment: 18 pages, 11 figures, 3 table
Thermo-optic and thermal expansion coefficients of RTP and KTP crystals over 300-350 K
We report new measurements of the thermal expansion and thermo-optic
coefficients of RbTiOPO (RTP) and KTiOPO (KTP) crystals over the
temperature range 300-350 K. For RTP/KTP our coefficients of linear thermal
expansion at 305 K are: /K,
/K, /K.
Our normalized thermo-optic coefficients at 632.8 nm and 305
K are: /K, /K, /K.Comment: 12 pages, 5 figures, 9 table
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