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Generation of a donut-shaped first-order Laguerre-Gaussian (LG01) vortex mode via a method designed to yield high mode purity is reported. Our approach utilises a novel twin-spot end-pumping scheme to directly excite the first order Hermite-Gaussian (HG01) mode in a solid-state laser, followed by a novel astigmatic mode converter based on spherical (concave) mirrors aligned at oblique incidence. A simple theoretical model for the mode converter is derived and from this the design approach is explained along with the potential benefits compared to conventional schemes based cylindrical-lens astigmatic mode converters, particularly for power scaling. As a proof-of-principle and to confirm the benefits of this scheme in terms of high mode purity we have applied it to an end-pumped Nd:YVO4 laser to generate a (LG01) beam with a controllable sense of azimuthal phase and hence orbital angular momentum. A method for characterising the resulting beam based on analysis of the spiral interference pattern derived with the aid of a Mach-Zehnder interferometer is described and yields a value for the LG01 mode purity of 94%. Common sources of mode impurity are identified and the prospects for scaling to higher power whilst maintaining high mode purity are considered.

We fabricate a saturable absorber mirror by coating a graphene- film on an output coupler mirror. This is then used to obtain Q-switched mode-locking from a diode-pumped linear cavity channel waveguide laser inscribed in Ytterbium-doped Bismuthate Glass. The laser produces 1.06 ps pulses at ~1039 nm, with a 1.5 GHz repetition rate, 48% slope efficiency and 202 mW average output power. This performance is due to the combination of the graphene saturable absorber and the high quality optical waveguides in the laser glass.

We present the hetero-epitaxial growth of high-quality crystalline Y3Ga5O12 onto a -oriented YAG substrate via pulsed laser deposition, using mixed ternary-compound and segmented binary-compound targets. We observe that a Y3Ga5O12 film fabricated using a segmented target (Y2O3/Ga2O3) contained ~ 100 times fewer scattering points than a film grown using a mixed Y3Ga5O12 target. We show that following ablation, the surface of the mixed compound (ternary) target had laser-induced cone structures, whereas the surface of single compound (binary) targets did not. It is concluded that the different ablation dynamics of the oxide constituents in the respective targets plays a significant role in the origin of the scattering points in the resultant films.

The Energy Transfer Upconversion (ETU) macroparameter is measured for Nd-doped GdVO4 and YVO4 samples at temperatures ranging from Room Temperature (RT) to 450K, by means of a simple and automated z-scan technique. Furthermore, the ground state absorption cross section into the 2H9/2+4F5/2 energy levels is characterised for both crystals over the same range of temperatures. The 808nm pi-polarisation absorption cross section is found to decrease from (58.6+-0.2) pm2 to (30.9+-0.6) pm2 for Nd:YVO4 and (54.0+-0.3) pm2 to (25.7+-0.5) pm2 for Nd:GdVO4, from RT to 450K. Over the same range the ETU coefficient decreases from (3.2+-0.7) e-16 cm3/s to (1.8+-0.4) e-16 cm3/s and (5.0+-0.5) e-16 cm3/s to (3.4+-0.2) e-16 cm3/s for nominally 0.5at.% and 1.0at.% Nd:YVO4 respectively, and (3.3+-0.5) e-16 cm3/s to (0.8+-0.2) e-16 cm3/s and (5.5+-0.5) e-16 cm3/s to (3.1+-0.3) e-16 cm3/s for 0.5at.% and 1.0at.% Nd:GdVO4.

We report pulsed laser deposition of high-quality crystalline yttrium aluminium oxide and yttrium gallium oxide with a growth rate approaching 20 μm per hour by using an excimer laser operating at a repetition rate of 100 Hz. This result demonstrates the capability of PLD at 100 Hz for upscaling deposition speeds to a rate that is industrially relevant. In addition, we show that use of this high repetition rate can cause additional heating of the substrate, which in turn affects the film composition. This effect is used as an additional control parameter on the composition, and thus refractive index, of the grown material.

Engineering the optical properties of waveguides is important for the optimization of their guided optical mode characteristics. Here, we document the dynamic control of the refractive index and composition of crystalline films, via the substrate temperature, during pulsed-laser-deposition growth of Er(1%)-doped yttrium gallium garnet on -orientated single-crystal yttrium aluminium garnet. An increasing substrate temperature is observed to reduce the gallium content in the grown film, with a corresponding reduction of refractive index. We demonstrate the ability to accurately control the refractive index via this technique and use it to grow a complex multi-core crystal waveguide. Our results highlight the potential of using pulsed laser deposition to fabricate crystal films with bespoke optical properties and thus engineer passive and active waveguide devices in situ.

The growth of a range of crystal garnets by pulsed laser deposition is presented. As a result of optimization of the fabrication process, films can now be grown with optical quality approaching that of bulk material. To demonstrate this, we present laser performance from a Yb:YAG film with 70% slope efficiency and >16 W of output power. In addition, we present the first pulsed laser deposition of laser quality Yb:GGG and Yb:YGG. Watt-level laser performance is achieved for these two gallium garnets and routes to further performance improvements and potential applications of these films are discussed.

We have used the technique of pulsed laser deposition (PLD) to grow doped crystalline films of garnets (YAG) and sesquioxdes (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 growth temperature required to grow crystalline thin films in comparison to ~2750K required to grow bulk crystals. We can grow these materials at the rate of ~4 µm per hour, on cheap and readily available single-crystal YAG substrates, which allows rapid production of waveguide samples of the ~10-20 µm thickness required for efficient pumping via high-power diode lasers.The sesquioxide films grow preferentially in the (222) crystal orientation, and although there is an excellent lattice match to the (100) oriented YAG substrates, the four-fold symmetry associated with the (222) growth direction can lead to the presence of domain boundary problems that contribute to an undesirable optical loss within these waveguide hosts. In contrast the garnet hosts experience ideal epitaxial growth (i.e. YAG films grown on YAG substrates) where the presence of the dopant lasing ion produces the necessary refractive index requirement for waveguide operation.We will discuss the range of lasing results we have achieved so far, which includes c.w. lasing within single waveguide films, capped layers and multilayer structures where the doped lasing layer has been grown within a 3-layer sandwich structure [1,2]. We will also describe results where a single layer of graphene has been deposited on either the output coupler mirror, or on the top surface of the guide, to produce pulsed laser output in q-switched mode [3-4]. Since these lasing waveguides are optically pumped by diode lasers, it is important to design these guiding structures to ensure efficient operation in terms of low threshold and high slope efficiency. Details will be given on optimum waveguide design as well as our strategy on further reduction of optical propagation losses.