1,721,251 research outputs found
Data for "Temperature induced modal changes of high power rod-type Yb-fiber amplifiers under various pump geometries and with noisy pump lasers"
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Supercontinuum decoherence due to XPM-assisted Raman amplification in normal dispersion fibers for polarization or wavelength offset pulses
No full textWe report the importance of cross-phase modulation (XPM) on the coherence of a low-energy probe pulse co-propagating with a high-energy pump pulse which generates incoherent supercontinuum in all-normal dispersion (ANDi) fiber due to Raman amplification of quantum noise. By investigating numerous fiber and pulse parameters we show consistently that for weak probe pulses the XPM from the pump is the dominant influence on the degradation of the probe coherence. We show that the faster decoherence at the pump leading edge means that the probe coherence is reduced more significantly when the probe has a higher group velocity, i.e., when an orthogonally-polarized probe is aligned to the fast (lower refractive index) axis of the fiber or when a co-polarized probe has a longer central wavelength. Simulations show that this effect occurs for both polarization maintaining (PM) and non-PM ANDi fibers and can result in a probe decoherence rate which is higher than that of the pump. These previously unreported results extend our earlier scalar simulations showing incoherent supercontinuum within a single pulse
Limits of coherent supercontinuum generation in normal dispersion fibers
Full text linkWe study the largely unexplored transition between coherent and noise-seeded incoherent continuum generation in all-normal dispersion (ANDi) fibers and show that highly coherent supercontinua with spectral bandwidths of one octave can be generated with long pump pulses of up to 1.5 ps duration, corresponding to soliton orders of up to N = 600. In terms of N, this corresponds to an approximately 50 times increase of the coherent regime compared to anomalous dispersion pumping. In the transition region between coherent and incoherent spectral broadening we observe the manifestation of nonlinear phenomena that we term incoherent cloud formation and incoherent optical wave breaking, which lead to a gradual or instantaneous coherence collapse of SC spectral components, respectively. The role played by stimulated Raman scattering and parametric four-wave mixing during SC generation in ANDi fibers is shown to be more extensive than previously recognized: their nonlinear coupling contributes to the suppression of incoherent dynamics at short pump pulse durations, while it is responsible for non-phasematched parametric amplification of noise observed in the long pulse regime. We further discuss the dependence of SC coherence on fiber design, and present basic experimental verifications for our findings using single-shot detection of SC spectra generated by picosecond pulses. This work outlines both the further potential as well as the limitations of broadband coherent light source development for applications such as metrology, nonlinear imaging, and ultrafast photonics, amongst others
The development of high power, pulsed fiber laser systems and their applications
Full text linkRare-earth doped silica fibers have been used for many years to create continuous-wave lasers, and Er-doped fiber amplifiers are now widely used in telecommunications. In addition, cladding pumped fiber allows the efficient conversion of multimode radiation from high power, low cost, broad-stripe semiconductor laser diodes into the single-mode emission of fiber lasers. With its broad gain bandwidth and high optical conversion efficiency, Yb-doped silica fiber represents an attractive medium for the generation and amplification of high energy ultrashort optical pulses. However, these potential advantages of Yb-doped silica fiber as a gain and nonlinear medium for mode-locked lasers and ultrashort pulse amplifiers have been less well studied, and it was not until 1999 that significant research interest first appeared in Yb-fiber chirp pulse amplifier (CPA) systems. This thesis describes the development of the first practical and stable, femtosecond, Yb-fiber oscillator, and of an Yb-fiber amplifier based CPA system (pulses ~10 µJ, <500 fs). Novel aspects of the system include the use of a high extinction ratio Electro-Optic modulator for pulse selection, and the development of a compact chirped-fiber-Bragg-grating (CFBG) pulse stretcher that provides both 2nd and 3rd order chirp compensation. Recently published theoretical results have demonstrated that the asymptotic solution for ultrashort pulses in a high gain fiber amplifier is a linearly chirped pulse, which can therefore be recompressed with a standard grating compressor. This thesis reports the first experimental comparison of nonlinear pulse evolution towards the asymptotic form using a cascaded amplifier system. The "direct amplification" system was constructed by removing the CPA stretcher grating, which also enabled the use of a less dispersive and more compact compressor. Further system development should lead to the generation of ultrashort pulses at high average power levels and >100 kHz repetition rates. Holey fiber (HF) is a recently developed technology that uses rings of air holes around a solid core to confine the optical field by average-index effects. Fibers are highly suitable for applications using nonlinear optics because of the tightly confined mode and long interaction lengths. The increased mode confinement possible using HF means that small-core, high air-fill fraction HF are an attractive nonlinear medium. Furthermore, the high index contrast in such fibers can create a strong (anomalous) waveguide contribution to the dispersion, and such HFs can have anomalous dispersion at wavelengths <1.3 µm, where conventional fiber has normal dispersion. Therefore HFs can support solitons in new wavelength bands. This thesis reports the first demonstration of linear dispersion compensation, soliton transmission, and visible continuum generation seeded by a 1.06 µm Yb-fiber source. In addition, an experimental study is reported that used HF seeded from a Ti:Sapphire laser to generate continuum in distinct transverse spatial modes of a HF. Numerical simulations suggested that the observed enhancement in UV generation from a higher order mode could be due to differences in the dispersion profiles of the fundamental and higher order transverse modes. Finally, the development of a novel source of <200 fs pulses, continuously tuneable in wavelength from 1.06-1.33 µm, based on the soliton self-frequency-shift principle, is described. The source was constructed from a diode-pumped Yb-doped HF amplifier, and the Yb-fiber oscillator described above. The diode pump power controlled the output wavelength
Robust phase retrieval using group-delay-dispersion-scanned second harmonic generation demonstrated in a femtosecond fiber chirped-pulse amplification system
No full textWe propose and demonstrate a phase retrieval method using a novel variant of the dispersion scan (‘d-scan’) technique via both simulations and experimental measurements on a femtosecond fiber laser. The method combines a map of group-delay-dispersion-scanned (d-scan) second-harmonic generation (SHG) spectra together with the fundamental spectrum as inputs. In order to ensure the technique is robust when pulse-to-pulse fluctuations are present, we use only the wavelengths of the resulting SHG peaks, and avoid the areas with low signal in the borders of the data trace. Simulations confirmed the phase-retrieval is accurate even with high levels of laser fluctuation. The trade-off is that pulses which have abruptly changing or highly modulated phase profiles are not retrievable. The d-scan uses the compressor gratings intrinsic to the fiber chirped-pulse amplification (CPA) systems so the method is low cost. For experimental verification, we used a 470 fs ytterbium-fiber CPA system, so the method is applicable to measurements on industrial fs fiber laser systems which generally have an order of magnitude less bandwidth than the Ti:sapphire lasers used to test earlier variants of the d-scan approach
Dataset for Robust phase retrieval using group-delay-dispersion-scanned second harmonic generation demonstrated in a femtosecond fiber chirped-pulse amplification system
No full textThis dataset supports the article entitled " Robust phase retrieval using group-delay-dispersion-scanned second harmonic generation demonstrated in a femtosecond fiber chirped-pulse amplification system", to be submitted to Journal of Quantum Electonics</span
Sub-microsecond pulsed pumping as a means of suppressing amplified spontaneous emission in tandem pumped fiber amplifiers
Full text linkWe propose a new tandem pumping scheme in three-level rare-earth doped optical fibers where energy storage in a pump fiber laser enables much shorter (~500 ns) pump pulses than is possible with pulsed diode laser pumping. This has the effect of reducing the time during which the final amplifier has high inversion and hence reduces the ASE when compared to continuous wave (c.w.) tandem pumping. We simulate the gain and ASE dynamics in a pulse-pumped Yb-doped fiber amplifier and show that the ratio of amplified signal to ASE background can be improved by up to 2 orders of magnitude over a large range of pulse energies compared to c.w. tandem pumping. Sub-micro-second pulsed tandem pumping offers a relatively straightforward, as yet experimentally untried, way to substantially reduce undesirable ASE compared to the levels in diode-pumped fiber amplifiers
Dataset for 'Overlapped pulsed pumping of tandem pumped fiber amplifiers to increase achievable pulse energy'
No full textDataset for the article:
A. Malinowski, J. H. V. Price and M. N. Zervas, "Overlapped Pulsed Pumping of Tandem Pumped Fiber Amplifiers to Increase Achievable Pulse Energy," in IEEE Journal of Quantum Electronics, vol. 53, no. 2, pp. 1-8, April 2017.
doi: 10.1109/JQE.2017.2657334
It has been reported previously that in the regime appropriate for amplifying femtosecond pulses using the chirped pulse amplification technique in Yb-fiber sources that sub-micro-second pulsed tandem pumping not only provides the thermal benefits of c.w. tandem pumping, but also enables strong suppression of ASE. In that case, the pump pulse preceded the signal pulse train. Here, we propose a tandem pumping scheme in rare-earth-doped fiber amplifiers, where a train of signal pulses is amplified by a pump pulse, which is almost exactly temporally overlapped. Simulations demonstrate that this can be used to create uniform gain across the signal pulse train, even at very high total pulse energies, where there would be significant gain shaping in the previous case. In addition, the pump is absorbed in a much shorter length, which increases the threshold for nonlinear effects and gain of greater than 26 dB is shown to be readily achievable in an amplifier as short as 1.5 m. This results in increased extractable energy before reaching the threshold for limiting nonlinear effects, such as stimulated Raman scattering. These attributes should be attractive for high energy, high average power, ultrashort pulse, coherently combined fiber laser systems.</span
Overlapped pulsed pumping of tandem pumped fiber amplifiers to increase achievable pulse energy
Full text linkIt has been reported previously that in the regime appropriate for amplifying femtosecond pulses using the chirped pulse amplification technique in Yb-fiber sources that sub-micro-second pulsed tandem pumping not only provides the thermal benefits of c.w. tandem pumping but also enables strong suppression of ASE. In that case, the pump pulse preceded the signal pulse train. Here we propose a tandem pumping scheme in rare-earth-doped fiber amplifiers, where a train of signal pulses is amplified by a pump pulse which is almost exactly temporally overlapped. Simulations demonstrate that this can be used to create uniform gain across the signal pulse train, even at very high total pulse energies where there would be significant gain shaping in the previous case. In addition the pump is absorbed in a much shorter length, which increases the threshold for nonlinear effects and gain of greater than 26 dB is shown to be readily achievable in an amplifier as short as 1.5 m. This results in increased extractable energy before reaching the threshold for limiting nonlinear effects such as stimulated Raman scattering. These attributes should be attractive for high energy, high average power, ultrashort pulse, coherently combined fiber laser systems
Sub-microsecond pulsed pumping as a means of suppressing amplified spontaneous emission in tandem pumped fiber amplifiers - Data in the figures
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