1,720,982 research outputs found
High Power Fiber Lasers for Industrial Applications
No full textFiber lasers can be considered a revolutionary technology in the laser field thanks to their unique properties, such as high efficiency, simplicity, compactness and robustness. These features have allowed in the last ten years their outstanding growth both in scientific and industrial applications, eroding the market share of traditional laser sources like solid-state and gas lasers. Fiber lasers power scaling to the kilowatt range is now well established and, thanks to the fiber confinement, excellent output beam quality can be obtained, with a remarkable benefit for applications. Today, high power laser sources are based on ytterbium doped, large mode area fibers because ytterbium can be efficiently pumped in the range 915nm − 975nm (where pump sources are widely available), generating laser action at 1060nm − 1090nm. With this configuration, impressive power scaling has been demonstrated in the last few years. This Ph.D. thesis has been focused on the design and development of high power fiber lasers for a wide range of industrial applications, like cutting, wending, drilling and micro-machining. Both continuous and pulse wave fiber lasers have been demonstrated and particular attention has been devoted to the development of critical technological de-vices like fused fibers combiner, strategic components either for pump light coupling into the laser active fiber (pump combiner) and for power scaling through the beam combining of several fibers lasers (signal combiner). Ytterbium doped fiber lasers have been developed during the Ph.D activity and, in particular, after a theoretical analysis devoted to the modeling of fiber laser cavities and amplifiers, a continuous wave fiber laser and two pulsed laser systems have been demonstrated. The CW fiber laser has been developed with a modular approach: 7 laser modules, capable of emitting hundreds of Watts each, have been coupled together thanks to a fused fiber combiner. A multi-kilowatts output power has been demonstrated. The photo-darkening effect in the active fiber of the laser modules has also been exper-imentally investigated. The pulsed architectures are instead a Q-switched MOPA and a Seed MOPA fiber lasers. The first system is based on a fiber laser oscillator operating in the Q-switching regime, followed by a power amplifier. This laser is capable of delivering 100ns pulses with 10W average power (2kW maximum peak power). The Seed MOPA consists instead of a current modulated laser diode followed by two amplification stages; 2W output average power with adjustable pulse widths from 10 to 100ns has been demonstrated. In the last part of the activity, a preliminary version of a thulium doped fiber laser emitting at about 2000nm (i.e. in the so-called eye-safe region) has been developed. The laser is a Seed MOPA system that has been tested in cw regime but in the near future the pulsed behavior will be investigate
Power Combiners with Feedthrough for Pumping of Fiber Lasers and Amplifiers
No full textIn a fiber laser, as well as in fiber-based master oscillator power amplifier (MOPA), pumping of the cavity is performed with low brightness, high power semiconductor laser diodes that deliver the pump light through a large core multimode fiber. The research hereby presented has been devoted to the development of a simple yet reliable procedure for packing a bundle of fibers that includes the feedthrough and fusing it to realize a power combiner for pumping high power fiber lasers
Investigation of collimating and focusing lenses impact on laser diode stack beam parameter product
Full text linkThe paper presents a new expression for determining the beam parameter product of a multi-emitter laser diode module made by stacking several single emitter chips. The proposed formula takes into account the effect of collimating and focusing lenses and has been validated experimentally, obtaining excellent agreement between theoretical expectations and measurements. A practical application to optimize the lenses' configuration for the design of a fiber-coupled multi-emitter module is also reporte
Application of Gaussian beam ray-equivalent model and back-propagation artificial neural network in laser diode fast axis collimator assembly
Full text linkThe paper presents the development of a tool based on a back-propagation artificial neural network to assist in the accurate positioning of the lenses used to collimate the beam from semiconductor laser diodes along the so-called fast axis. After training using a Gaussian beam ray-equivalent model, the network is capable of indicating the tilt, decenter, and defocus of such lenses from the measured field distribution, so the operator can determine the errors with respect to the actual lens position and optimize the diode assembly procedure. An experimental validation using a typical configuration exploited in multi-emitter diode module assembly and fast axis collimating lenses with different focal lengths and numerical apertures is reporte
Artificial neural network assisted laser chip collimator assembly and impact on multi-emitter module beam parameter product
No full textA new tool based on artificial neural networks to assist in the accurate positioning of the lenses used to collimate the beams emitted by the individual chips forming multi-emitter diode laser modules is presented. An alternative expression for the evaluation of the obtained beam quality is disclosed and the impact of different choices on the overall module performance in terms of beam quality and coupling efficiency into a collecting fiber is analyzed. Experimental validations with different combinations of lenses are reported to prove the effectiveness of the proposed approach
Development of a 300W 105/0.15 fiber pigtailed diode module for additive manufacturing applications
Full text linkThe paper reports on the design, manufacturing and preliminary characterization of a new compact and high beam quality laser diode multi-emitter module able to deliver about 300 W in a standard 105/125 fiber with 0.22 numerical aperture and 95% of power is in NA 0.15. The layout exploits a proprietary architecture and uses a plurality of 905 nm and 940 nm chips properly combined through spatial, polarization and wavelength multiplexing. Given its small footprint and low ownership costs, the module has been specifically devised as a direct diode laser source for small/mid size metal powder based additive manufacturing machines
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Fabrication of Pump Combiners for High Power Fiber Lasers
No full textA custom fabrication procedure for pump combiners matched to a wide variety of double-clad fibers used in high power fiber lasers has been developed. Both combiners with and without feedthrough can be fabricated with an improved repeatability thanks to a specific mechanical setup that simplifies placing the fibers in their proper location within the input bundle before the tapering and fusion processes. Extensive characterization results on 7-to-1 and on (6+1)-to-1 combiners are confirming the validity of the proposed approac
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