Crystalline planar waveguide lasers fabricated by pulsed laser deposition
This work describes the fabrication and performance characteristics of crystalline planar waveguide lasers produced by the pulsed laser deposition technique. This project was undertaken to establish that the pulsed laser deposition technique could be utilised to manufacture crystalline planar waveguide lasers with both rare earth and transition metal dopants. In the first instance a crystalline layer of neodymium doped Gd3Ga5O12 was grown on a Y3Al5O12, substrate. This structure was made to lase at ~1.06µm when pumped at 808nm using a Ti:sapphire laser. This result constitutes the first report of lasing in a pulsed laser deposited film. Further refinement of the deposition procedures resulted in a much improved set of films with waveguide losses as low as 0.5 dB/cm and absorbed pump power thresholds as low as 2.2mW. In the second case layers of Ti:sapphire (Ti doped a-Al203), of around 10 µm thickness, were grown on undoped sapphire substrates. These layers were examined by ion beam channelling and x-ray diffraction techniques which show that they have a level of crystalline perfection equal to the bulk grown material. The fluorescence. spectrum was also shown to be of the same form as that obtained from the bulk. These layers were also shown to be waveguiding. Finally, one such Ti:sapphire waveguide was made to lase around 800nm, when pumped with an argon ion laser. This was done with an absorbed pump power threshold of 0.56W using high reflectivity mirrors. A maximum quasi-CW output power of 357mW was achieved for an absorbed pump power of 3.44W using an output coupler with 35% transmission. True CW operation was also achieved, the first demonstration of CW lasing in a transition metal doped waveguide produced by pulsed laser deposition.