Pulsed laser deposition of thick multilayer garnet crystal films for waveguide laser devices
The main aim of this project was to use the technique of pulsed laser deposition (PLD) to fabricate thick multilayered garnet crystal planar waveguides with rare-earth ion doped cores for use as planar waveguide laser devices. Planar waveguides are of interest because of the implications of their structure, which allows for lasing, pumping and heat dissipation to each have a unique axis of operation, and the confinement properties of planar waveguide lasers result in lower pump power thresholds, higher gains per unit pump power and higher efficiencies than their bulk counterparts. Thick planar waveguide lasers are desirable because they can be pumped by high power diode laser arrays, and suffer less from the detrimental effect of particulates (a practically unavoidable side effect of the PLD technique). The use of multilayers allows a device with a high numerical aperture to be fabricated and the careful choice of the cladding layer thicknesses and refractive indices allows good beam quality output to be produced using diode pumping. Other aims of the project were to fabricate a self-imaging waveguide amplifier and explore other applications of thick garnet crystal films such as the possibility of using a highly doped thick film as a thin-disk laser device. Now that the technique of thick garnet crystal film deposition via multiple growth runs has been established, the potential of thick garnet crystal films needs to be exploited. Multilayer structures with more ideal geometries need to be fabricated to make optimal waveguide laser devices and difficulties resulting from thermal expansion mismatch need to be addressed so that side-pumping can be performed with diode laser arrays.