A detailed quantitative model for the strengthening of monolithic alloys and composites due to precipitation strengthening, solution strengthening, grain and subgrain strengthening, strengthening by dislocations and load transfer to ceramic inclusions is presented. The model includes a newly derived description of the effect of a precipitate free zone (PFZ) around the reinforcing phase incorporating strain hardening of the PFZ. The model is successfully applied to model the experimental data for the proof strengths of four Al-Li-Cu-Mg type alloys and composites aged to obtain a wide range of microstructures and all strengthening contributions are quantified. It is shown that PFZ formation in the 8090 MMC causes a drastic reduction in the proof strength (about 100 MPa), but it has little influence on the time required for peak ageing. In all alloys strengthening due to GPB zones is more important than strengthening due to δ' (Al 3 Li) phase.

High-power operation of a broadband superfluorescent fiber source has been achieved via the process of amplified spontaneous emission (ASE) in a double-clad Yb-doped multimode-offset-core fiber by using a novel fiber-end termination geometry to suppress lasing. The fiber was cladding pumped by a high-power diode source at 976 nm and yielded a maximum ASE output of 63 and 47 W from the two ends of the fiber, respectively. The maximum combined ASE output was 110 W with slope efficiency with respect to launched pump power of up to 68%. The wavelength spectrum of the ASE source spanned the range from approximately 1032 to 1120 nm, and the bandwidth (FWHM) of the emission spectrum was 40 nm. The output beam was slightly multimode with a beam-quality factor (M2) of 1.6. The prospects for further improvement in performance are considered.

A novel approach to achieving robust single-spatial-mode operation of cladding-pumped fiber lasers with multimode cores is reported. The approach is based on the use of a fiber geometry in which the core has a helical trajectory within the inner cladding to suppress laser oscillation on higher-order modes. In a preliminary proof-of-principle study, efficient single-mode operation of a cladding-pumped ytterbium-doped helical-core fiber laser with a 30 microm diameter core and a numerical aperture of 0.087 has been demonstrated. The laser yielded 60.4 W of output at 1043 nm in a beam with M2 < 1.4 for 92.6 W launched pump power from a diode stack at 976 nm. The slope efficiency at pump powers well above threshold was approximately 84%, which compares favorably with the slope efficiencies achievable with conventional straight-core Yb-doped double-clad fiber lasers.

High-power operation of a cladding-pumped Tm-doped broadband superfluorescent fiber source in the two-micron wavelength regime is described. Predominately single-ended operation was achieved using a simple all-fiber geometry without the use of a high reflectivity mirror or fiber Bragg gratings. The source produced >11 W of single-ended amplified spontaneous emission output spanning the wavelength range from approximately 1930 nm to 1988 nm for a launched diode pump power of approximately 40 W at approximately 790 nm, corresponding to a slope efficiency of 38% with respect to launched pump power. The wavelength spectrum of the superfluorescent source spanned the range from approximately 1650 to 2100 nm with a bandwidth (FWHM) of > 100 nm for output power levels of < 20 mW.

In this work a volume Bragg grating is used as a wavelength selective element in a high-power cladding-pumped Yb-doped silica fiber laser. The laser produced 138 W of linearly-polarized single-spatial-mode output at 1066 nm with a relatively narrow linewidth of 0.2 nm for approximately 202 W of launched pump power at 976 nm. The beam propagation factor (M(2)) for the output beam was determined to be 1.07. Thermal limitations of volume Bragg gratings are discussed in the context of power scaling for fiber lasers.