Ytterbium-doped crystals and glasses are used for very high-power lasers and amplifiers and also to generate femtosecond pulses in ultrafast mode-locked lasers at wavelengths near 1 μm. For practical and efficient applications, such materials need to have a spectrally broad and tunable emission together with a high-power and short-pulse output. Disordered Yb-doped borates are ideal candidates, since they display extraordinary spectroscopic properties such as sub-100 fs pulse generation with glass-like broad-wavelength tuning. They can also be highly doped, thus enabling high-power output. To provide new insights into the properties of such materials, the authors of this work did a complete structural description of a 5 at. % Yb-doped GdCB disordered crystal, as well as a 3D modeling showing the atomic surroundings of the disorder-related cationic sites. Unlike other works, this study comprises polarized and low-temperature spectroscopy measurements. Results showed that broadband spectral properties were preserved even for low temperatures with bandwidths of more than one order of magnitude broader compared to ordered crystals. Excellent power-scaling capability is reported, as well as extremely broad and smooth gain spectra with lasing gain bandwiths of about 50 nm. The authors propose that this material has high potential for the generation of sub-50 fs pulses from passively mode-locked Yb-doped GdCB crystal laser, for efficient and power-scalable laser operation for ultrafast amplifiers.

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