PLD growth of complex waveguide structures for applications in thin-film lasers: a 25 year retrospective

We have been using PLD to grow doped crystalline films of a range of laser hosts that include garnets (YAG, GGG and other variants), sapphire and, most recently, cubic sesquioxides (Y2O3, Sc2O3, and Lu2O3) for application as optically-pumped waveguide lasers. For the sesquioxides in particular, PLD offers a real advantage in terms of the ~1100K temperature required to grow crystalline thin films in comparison to ~2750K required to grow bulk crystals. We have grown these materials at deposition rates of up to ~5 µm per hour, on cheap and readily available single crystal substrates, which allows rapid production of waveguide samples of the ~10-30 µm thickness required for efficient pumping via high power diode lasers.We will describe the range of PLD techniques we have used to date, that include single-beam, multi-beam, consecutive and combinatorial as well as fast shuttering of multiple laser sources onto different targets. We will discuss strategies we have adopted to grow complex structures in both the vertical and horizontal planes of the waveguides, including multilayers, capped, graded and volume Bragg structures. Finally we will describe post-processing we have performed on the waveguides to improve the final mode quality of the lasing output produced, and to generate q-switched output via local deposition of graphene that acts as a Q-switch. Our current levels of lasing output are approaching 20W in c.w. mode, and we will describe our strategy to exceed this via a MOPA structure using multiple PLD-grown waveguides