I propose to demonstrate the first optical frequency comb systems where the tooth spacing is tuneable by many free spectral ranges, and use this to introduce novel spectroscopic techniques and applications in selected areas of metrology, spectroscopy and medicine, creating both significant scientific and commercial impact. The proposed comb system combines repetition frequency tuneable femtosecond pulse surface emitting semiconductor lasers with ytterbium fibre amplifier systems (YDFAs) and photonic crystal fibre (PCF) to enable this novel comb capability. The physical properties of the comb system, from the noise characteristics of the semiconductor laser at its centre, to that of the complete system will be investigated and compared to the current state of art systems. A tuneable gigahertz repetition frequency source will enable the study of vibrational modes in nano-scale objects. For example PCF has radial vibrational modes in the GHz range, as do the protein shells of viruses. We will study these resonances by developing new spectroscopic techniques enabled by the tuneable comb system. We will study the enhancement and suppression of nonlinearities in PCF by resonantly exciting vibrational modes. We will also study the inactivation of viruses by resonantly exciting vibrations in their shells, causing them to break up. The classic frequency comb has followed a development path similar to the laser; at its inception no one could imagine the vast range of applications it has enabled. The novel capabilities of this comb system will similarly enable many future applications and measurement techniques which will only be envisaged as the capability and international exposure of this system increases. A key to the continuing success of the research theme started beyond this proposal will be strong national and international collaborations. I have established a strong and broad ranging network of collaborators and will continue to build this network throughout the proposal to enable this research to set the agenda and lead this new field into the future.