We present here the development of ultra-low NA large mode area neodymium doped alumino-phospho-silica fibers with different clad-to-core ratios for high power laser emission around 910nm. This ratio is determinant in the competition between the 3-level transition at 910nm and 4-level transition of neodymium at 1060nm. The study shows that the 30/130µm (core/cladding) fiber was the most efficient, with a record output power of 83W at 910nm, yielding a 47% slope efficiency and a good beam quality (M²~1.5). Parasitic power at 1060nm was kept lower than 1W and no sign of roll-off was observed at maximum pump power.
We present in this work, the development of a nanosecond pulsed Master-Oscillator Power-Amplifier (MOPA) laser system near 905 nm based on the 3-level transition of Neodymium using a novel low NA polarization-maintaining Nd-doped silica fiber with a 30µm core and 130µm cladding. The MOPA delivered up to 24 W of average power (0.6 mJ energy per pulse) with good beam quality (M²~1.4). Cascaded LBO and BBO crystals are used respectively for second-harmonic generation and fourth-harmonic generation, giving respectively average output powers of 4.9W at 452nm (conversion efficiency of 20%) and 550mW at 226nm (conversion efficiency of 10%).
We present the fabrication by Surface Plasma Chemical Vapor Deposition (SPCVD) and All Solution Doping (ASD) of step-index Nd-doped fibers with a 30/125μm (core/cladding diameters) geometry and a low numerical aperture (NA) near 0.05. A phospho-alumino-silicate (SiO2-Al2O3-P2O5-Nd2O3) core composition was used to reduce the formation of Nd3+ ions clusters while keeping a low refractive index through the peculiar AlPO4 chemical complex. Operated in CW laser regime, a 0.053 NA fiber generated up to 17W of output power at 921nm, limited by the available pump power at 808nm (51W), yielding a 37% power conversion efficiency. The profile of the output beam for a bend diameter of ~12cm is gaussian and nearly diffraction limited (M2 ~1.1). This is in good agreement with the large discrepancy, in terms of calculated bending losses, between the fundamental LP01 and the higher order modes.
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