Ti:sapphire waveguide laser by the thermal diffusion of Ti into sapphire
This thesis reports the first realisation of a Ti:sapphire channel waveguide laser by the thermal diffusion of titanium(Ti) into a sapphire wafer. The Ti-diffused region provides both the optical gain medium and the optical waveguide. These results comprise the first realisation of Ti3+ diffusion in sapphire and the first realisation of optical waveguides in sapphire by diffusion doping. The attraction of the Ti:sapphire laser in a planar waveguide configuration is its potential as a compact, broadly tunable source over 400nm in the near infra-red, which would provide a versatile radiation source for sensing or spectroscopy. The basis for the Ti:sapphire laser formed in a waveguide geometry by diffusion doping is discussed, and a simple model indicates that pump power thresholds less than 100mW are achievable. Previous work on the difhsion of metals into sapphire is reviewed, indicating that temperatures as high as 1950°C are appropriate for initial experimental work. Processes, equipment and characterisation techniques are presented that enable the investigation of Ti diffusion in sapphire. Spectroscopic characterisation of the diffused material indicates that fluorescent Ti3+ ions are incorporated, appropriate for use as an optical gain medium. The diffused Ti distribution is investigated following diffusion at temperatures between 1480°C and 1950°C over diffusion times between 0.2 and 8 hours, achieving depths in excess of 50μm and peak Ti3+ concentrations greater than 0.4wt% Ti2O3 in Al2O3. Following diffusion from a series of stripe sources, a fast lateral diffusion is observed. Slab and channel waveguides are formed in the Ti-diffused sapphire and trends in the effective refractive index, mode intensity profiles and spectral attenuation are reported. Channel waveguides appropriate for the realisation of a miniature laser are identified. Ti:sapphire waveguide lasers are reported for two cavity configurations, with operation at wavelengths between 770nm and 810nm. With 7% output coupling, a pump power threshold of 1.2±0.4W and slope efficiency of 0.5% is achieved. This first realisation of a waveguide laser by the thermal diffusion of titanium into sapphire clearly demonstrates the feasibility of this approach to the realisation of a miniature broadly tunable Ti:sapphire waveguide laser.