We developed a new holmium-doped triple-clad fiber (Ho-3CF), reducing the clad diameter to improve the overlap between pump and doped-core, and the holmium concentration to reduce the influence of ion clustering on the laser efficiency. We illustrate here the performance of this fiber in a laser oscillator configuration. The laser emission is centered at 2.12 µm by a fiber Bragg grating, and the active fiber is pumped in the clad by a 1.94 µm thulium-doped fiber laser. The slope efficiency reaches 60 %, for a maximum signal power of 62 W delivered on a quasi single spatial mode (M 2 =1.2). To the best of our knowledge, this slope efficiency is the highest reported for a high power clad-pumped fiber laser emitting at a wavelength higher than 2.1 µm. We also analyze experimentally the impact of the pump Numerical Aperture (NA), at the input of the Ho-3CF, on the laser efficiency. Finally, we use our numerical simulation to comment on the best choice of pump wavelength.
The X‐ray radiation‐induced attenuation (RIA) growth kinetics are studied online in different single‐mode aluminosilicate optical fibers in the near‐IR (NIR) domain to evaluate their potential in terms of dosimetry. The optical fibers differ by Al contents, core sizes, drawing parameters, and also by a preform deposition process. The data show no dependence of the RIA on all these parameters, a positive result for the design of point or distributed radiation detectors exploiting RIA to monitor the dose. The RIA growth rate is unchanged for dose rates changing from 0.073 to 6.25 Gy(SiO2) s−1, and the RIA linearly increases with the dose up to 2 kGy(SiO2). Small but noticeable RIA changes are observed when the irradiation temperature increases up to 50 °C during successive irradiation runs. Such results, and the post‐irradiation RIA recovery, have to be considered for the application, as they can affect the dose measurement accuracy. Finally, the spectral analysis shows no dependence of the spectral shape on the fiber and irradiation parameters. As a consequence, the data reported at 1310 and 1550 nm give information not only for the RIA kinetics at telecommunications and sensor wavelengths but also for the whole NIR range often used fiber‐based technologies.
We present the first frequency-quadrupled linearly-polarized Q-switched neodymium-doped fiber laser generating > 500 mW average power at 226 nm. For this purpose, an amplified Q-switched oscillator using novel large-mode-area (LMA) fibers and generating up to 24 W average power (15 kW peak power) at 905 nm was developed. Two nonlinear frequency conversion stages using a LBO crystal for SHG and a BBO crystal for FHG generate respectively up to 4.9 W average power in the deep blue at 452 nm and a maximum of 510 mW average power in the deep ultra-violet (DUV) at 226 nm. Performance limitations and further improvements are discussed.
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