94 research outputs found
Nested-ring Tm-doped high-power widely tunable fiber laser
No full textA structured thulium-doped nested-ring active fiber was used to build a widely tunable high-power fiber laser. The nested-ring fiber allows high-power cladding pumping along with enhanced thermal management, improvement in the efficiency of the two-for-one process, and enabling single-mode operation. The straightforward tunable cavity design permits remote tuning while ensuring full enclosure of free-space optics and purification with nitrogen to mitigate the effects of water vapor absorption on the lasing process. Our study introduces a tunable Tm-fiber laser capable of emitting in the 1930 to 2090 nm range with a linewidth of 0.2 nm, delivering stable output power up to 70W.</p
Monolithic 272W high efficiency Tm-doped nested-ring fibre laser
No full textThulium fibre lasers represent an important system in applications such as medical treatments, materials processing, remote sensing, non-linear frequency conversion, LIDAR, and defence applications [1]. High-power thulium lasers are mainly based on 790 nm cladding pumping schemes, which allow exploitation of a two-for-one cross-relaxation process with theoretical efficiency up to 80 %. However, power scaling beyond 150 W, in general, requires utilisation of LMA fibres, which suffer from lower efficiencies [2]. The nested-ring fibre was proposed to investigate the power-scaling potential of a novel non-uniform Tm doping profile employed across a small core diameter without pedestal. The confinement of Tm
3+ doping to a thin ring towards the outer edge of the fibre core reduces the spatial overlap between the propagating mode and the doped region. This allows efficient operation at the shorter wavelengths without the onset of parasitic lasing at longer wavelengths. Crucially, this design also reduces pump absorption per unit length, while still maintaining a high Tm
3+ doping concentration within the doped region of the core (4 wt. %), to allow efficient exploitation of the two-for-one cross-relaxation process. This reduces the thermal load density of the fibre, allowing for a greater power extraction before thermally-induced failure [3].</p
Monolithic highly-efficient 272 W nested-ring structured-core thulium fibre laser at 1940 nm
No full textA novel, to the best of our knowledge, thulium-doped silica fiber with a non-uniform core doping profile has been utilized to demonstrate a high-power monolithic laser oscillator system. The fiber laser achieved a continuous-wave (CW) output power of 272W at 1940nm with slope efficiencies of 68% and 71% with respect to launched and absorbed pump power, respectively. This novel Tm fiber design enabled the generation of the highest reported output power from a single-mode, small core (<15µm diameter) non-pedestal fiber. Moreover, the slope efficiency achieved is the maximum reported to date for a single-mode thulium fiber laser operating at >100 W output power level.</p
Coherent beam combining of self-adaptive lasers
No full textThe novel technique of phase conjugate self-organised coherent beam combination is reported. It is demonstrated that due to the spectral mode freedom of a phase conjugate self-adaptive laser that efficient "all-passive" combination of many high quality lasers can be achieved. Efficient combination (>92%) of two modules has been experimentally demonstrated to >30W in continuous wave operation. Recent results demonstrating pulsed operation are also reported
Narrow-band wavelength-tunable thulium fiber ring laser
No full textLaser sources with flexibility in operating wavelength have applications in a number of areas including: remote sensing and monitoring, spectroscopy and metrology. For many of these applications the requirements for wavelength flexibility and good beam quality are very often accompanied by the need for a relatively narrow bandwidth and, in some cases, also by the need for rapid wavelength scanning. Rare earth doped fiber lasers offer versatility in operating wavelength due to the broad linewidths associated with glass hosts, but simultaneously achieving wavelength agility and a narrow lasing bandwidth is rather challenging
Acousto-optic devices for operation with 2 µm fiber Lasers
No full textFibre lasers operating in the 2µm region are of increasing interest for a range of applications, including laser machining and biomedical systems. The large mode area compared to 1µm fibre lasers combined with operation in an “eye-safe” region of the spectrum makes them particularly attractive. When developing fibre lasers at 1µm and 1.5µm manufacturers were able to call upon enabling technologies used by the telecoms industry, but at longer wavelengths, including 2µm, many such components are either unavailable or immature. We report on recent developments of Acousto-Optic Modulators and Tunable Filters that are specifically optimised for use with fibre systems operating at or around 2µm. AO devices are interesting due to their ability to conserve spatial-coherence, making them appropriate for use with single-mode optical fibres. We describe how the choice of interaction medium is an important consideration, particularly affecting the drive power and the polarisation behaviour of the device – the latter being an important parameter when used in a fibre system. We also describe two designs of AO Tunable Filter intended for laser tuning. Both designs have been demonstrated intracavity in 2µm fibre lasers. The first gives exceptionally narrow resolution (δλ/λ<0·1%). The second design is of a novel type of AOTF where a matched pair of AOTFs is configured to give a substantially net zero frequency-shift with little or no loss of pointing stability, any minor deviations in manufacture being self-compensated. Furthermore, small controlled frequency-shifts (up to about 10kHz) may be introduced with little or no detriment to the alignment of the system
Hybrid Ho:YAG laser with 50W radially-polarised output
No full textHolmium doped radially polarised lasers operating in the 2.1 µm spectral region are of great interest as they provide benefits of operation in the atmospheric transmission window (2.1-2.25 µm), absorption in transparent polymers, as well as the materials processing benefits that are beginning to be realised from utilising select higher order modes [1]. We report on the development of a 50W CW radially polarised Ho:YAG laser operating at 2090nm
MLMCLangevin code
No full text<p>Set of C++ classes for integrating the Langevin equation using Monte Carlo integrators with different time stepping methods. Both Standard Monte Carlo and more advanced Multilevel Monte Carlo methods are supported. The code can be used to solve several SDEs:</p>
<ul>
<li>Simple test cases, such as propagation in a quadratic and quartic oscillator potential</li>
<li>Propagation of particles in a turbulent velocity field in the atmospheric boundary layer</li>
</ul>
<p>For more details see https://bitbucket.org/em459/mlmclangevin</p>
<p>The code provided here can be used to reproduce the results in the paper "Multilevel Monte Carlo and Improved Time Stepping Methods in Atmospheric Modelling" by Grigoris Katsiolides, Eike Mueller, Robert Scheichl, Tony Shardlow and David Thomson. (tag 'JCPpaper', SHA a15897e in bitbucket repository)</p>
Holmium doped fibre optimised for resonant cladding pumping
No full textOptimisation of Holmium doped double clad fibre to provide low loss 2μm pump guidance is reported. CO2 laser based cladding shaping and all glass guidance is demonstrated to provide 67% double-clad laser slope efficiency
Multi-watt operation of a holmium doped silica fibre laser at 2.2 µm
No full textLaser sources operating in the atmospheric transmission window between 2.1 and 2.25 µm are of interest for a range of applications (e.g. remote sensing, free-space communication and defence). Holmium fibre lasers provide good coverage of the lower part of this spectral region [1], but operation towards 2.2 µm is much more challenging due to a reduced emission cross-section and higher propagation losses associated with the IR absorption edge of fused silica. Furthermore, OH- -contamination can cause additional absorption around 2.2 µm. Here we investigate the limits of long-wavelength tuning of a holmium-doped fibre laser, and report, to the best of our knowledge, the first watt-level (4.1 W) output from a silica fibre laser operating at 2.2 µm
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