Geoffrey Pert has conducted pioneering work, both theoretical and experimental, in the design of UV laser systems. At a time when the main thrust was towards true X-ray systems, Geoffrey independently decided to design systems based on recombination in laser-produced plasmas, to work at wavelengths of 100 angstroms and to approach shorter wavelengths by scaling from there. His realisation of the crucial role of resonant line trapping was followed by its resolution by motional Doppler effects in an expanding plasma. This led first to the theoretical design and then the actual construction of the carbon fibre laser. Early results showing gain were received with scepticism but a final convincing demonstration of gain was made at the Central Laser Facility in 1985. Geoffrey proposed the coating of carbon fibres to move to shorter wavelengths, and gain was demonstrated for lithium-like ions of aluminium and chlorine. He is now involved in moving laser wavelengths into the ‘water window’ at which point important applications, for example X-ray microscopy of biological materials, become possible.