Design, characterizaion and fabrication of neodymium doping profiles in transparent YAG ceramics.

摘要

Transparent laser ceramics offer significant fabrication advantages over traditional cubic-oxide single-crystal fabrication techniques, such as reduced processing time, scaling to large aperture sizes and reduced fabrication temperatures. Ceramic fabrication also allows a convenient route to engineering spatially-varying rare-earth doping profiles by creating a composition profile in the green-ceramic state. Optimized doping profiles have the potential to simultaneously improve diode-pumped laser efficiency and beam quality.; The ability to arbitrarily engineer the doping profile of laser media opens a very large design space. The process of optimizing the doping profile for improved performance is dependent on the laser geometry (i.e., slab, rod, thin-disk, etc.) and is complicated by the change in thermal conductivity and refractive index of the host with doping level. In addition, spatially varying the rare-earth-ion concentration changes the distribution of thermal load within the gain medium. Without careful consideration, temperature-induced distortions will greatly reduce beam quality. To balance the multiple profile design constraints, a genetic algorithm was used to optimize the power delivered into diffraction-limited spot in the far field. The gain medium was composed of an Nd:Y3Al5O12 (Nd:YAG) zig-zag slab amplifier, edge pumped with 10 kW of diode pump power at 807.5 nm. The resulting doping profile is predicted to increase the power extracted from the laser and delivered into the far field by over 39% compared to the uniformly doped laser media that can be fabricated today.; A simple Nd:YAG-core, YAG-clad planar waveguide structure was also fabricated. For the first time, laser oscillation was demonstrated in a 500-mum-wide doping profile fabricated directly from a green ceramic. However, the use of a reactive sintering method (Al2O3 and Y2O 3 reacted to produce Y3Al5O12 during sintering) to fabricate this structure is shown to transport significant amounts of Nd through the grain boundaries, which greatly distorts the initial profile. Current ceramic fabrication techniques can reliably make large doping profiles, such as the profile outlined above. However, to create practically useful waveguides directly from green ceramics, a new material system or a significant reduction in fabrication temperatures is required.