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The sesquioxides yttria, scandia and lutetia have been identified as promising host materials for high power lasers due to their excellent thermal properties, their ability to incorporate RE-ions and their resulting spectroscopic properties [1]. However, the melting points of these materials exceed 2400°C and are therefore problematic to grow from the melt. Pulsed laser deposition (PLD) is an alternative method of growing thin crystalline films of these materials, avoiding the requirement for such high temperature growth.

Pulsed waveguide lasers are interesting sources for a wide range of applications ranging from medicine, industrial processing and defence. Waveguides offer monolithic integrated structures with a natural geometric compatibility with high-power diode laser pump sources allowing compact devices. Additionally, if propagation losses can be kept low, the optical confinement can lead to low laser thresholds, high efficiencies, and low power requirements for passive Q-switching or mode-locking via saturable absorbers (SAs). Rare-earth-doped sesquioxide materials, such as yttria, possess physical and spectroscopic properties that make them very interesting for high-power solid-state lasers, and we have recently reported Q-switched operation of a pulsed laser deposited (PLD)-grown Yb:Y2O3 waveguide using a graphene-covered output coupler as an SA. The output power of this laser was limited by damage to the graphene layer, which is directly in the path of the laser beam. However, waveguides also offer the opportunity of coupling the laser beam to the saturable absorber via evanescent-field coupling and this in turn offers the possibility of high-power pulsed operation.In this paper, we demonstrate an Yb:Y2O3 waveguide laser Q-switched using evanescent-field interaction with graphene. 310 nJ pulses at an average power of 456 mW were obtained from a graphene-covered Yb:Y2O3 waveguide, which represents more than an order of magnitude improvement when compared to previous Q-switched waveguide lasers using end-butted graphene.

The concentration dependence of energy transfer upconversion in Nd:YAG is investigated via the z-scan technique. The ETU coefficient is determined to increase from 35×10-18 cm3/s to 90×10-18 cm3/s when the concentration increases from 0.3 at.% to 1.1 at.%.

Thin film sesquioxide waveguide layers fabricated via pulsed laser deposition are characterised by XRD. We show that the crystal growth orientation affects the crystalline structure and the optical propagation performance of the waveguides.