High-power planar waveguide visible-lasers.

Lasers have become ubiquitous in our daily lives, underpinning much of our technology dependent society. No longer a solution looking for a problem ; lasers are a tool in their own right. Many different solid-state laser configurations have evolved since the inception of the laser, the majority are based on rare-earth (RE) ions and produce coherent radiation in the near-IR. In some cases, multi-kW power levels that can cut through centimetres of steel in seconds are available. The light emission from these lasers starts from low-lying meta-stable excited states of the RE ions; however, many applications exist, such as display technologies, diagnostic tools at the life-science interface, or capitalising on the transmission window of seawater for sub maritime sensing and communications, which require higher-energy photons, that is, visible light. Such wavelengths can be obtained through non-linear frequency upconversion of IR lasers or directly through stimulated emission originating from higher-lying RE-ion excited-states. Solid-state visible lasers based on emission from these higher-lying excited states are still a research laboratory phenomenon, typically with low powers and low efficiencies and a limited range of wavelengths. The principle technical challenge restraining these devices is an effective pumping cycle that avoids loss generating mechanisms such as parasitic upconversion and photo-darkening, which, for example, have so far foiled the commercialisation of upconversion-pumped visible fibre lasers. We present a new approach for generating visible output from RE ions that will expand the toolkit of the laser user. Drawing upon our pioneering research and expertise with recent and critical technological advancements, namely ultra-low-loss rare-earth-doped crystalline waveguides and narrow-linewidth high-power diode-laser pump sources, we can now for the first time generate the right pump excitation parameters that will enable efficient high-power operation of this laser architecture. Our vision is to simplify the solid-state visible laser to just a single oscillator, while simultaneously broadening its capabilities through exploiting the rich spectroscopic properties of the higher-lying excited-states for generating different colours, and, their unique energy storage capacity. A power-scalable architecture will be realised, demonstrating applicability to high-power operation in both continuous wave (cw) and pulsed modes of operation, with unrivalled characteristics compared to alternative solid-state systems. Successful demonstration of the milestones in this project will place the UK at the forefront of international research in the field of high-power visible solid-state lasers, with an excellent opportunity to commercialise the technology through our industrial partners.