Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.

The aim of this proposal is to demonstrate for the first time a semiconductor laser emitting transform-limited optical pulses of less than 200 fs duration in a diffraction-limited beam. This achievement will open the way for the development of truly compact ultrafast optical systems. Our device is a surface-emitting laser, optically pumped using the cheap and rugged technology developed for diode-pumped solid state lasers, with perfect beam quality enforced by an extended cavity. It emits a periodic train of ultrashort pulses at a repetition rate of a few GHz using the optical Stark effect passive mode-locking technique introduced by the Southampton group. Recent proof-of-principle experiments have shown that these lasers can generate stable 260-fs pulse trains. We have shown, moreover, by modelling and by experiment, that the optical Stark mechanism can shorten pulses down to durations around 70 fs, comparable with the quantum well carrier-carrier scattering time. Our proposal is to build on these world-leading results with a systematic exploration of the physics of lasers operating in this regime. The key is to grow quantum well gain and saturable absorber mirror structures in which dispersion, filtering and the placing of the quantum wells under the laser mode are controlled to tight tolerances. We shall achieve this using molecular beam epitaxy to realise structure designs that are developed with the aid of rigorous numerical modelling of the optical Stark pulse-forming mechanism. We shall also use femtosecond pump and probe spectroscopy to determine the dynamical behaviour of our structures in this regime directly. For these pioneering studies, the compressively-strained InGaAs/GaAs quantum well system operating around 1 micron is most suitable; and this is where we shall work; however, the devices that we develop can in principle in future be realised in other material systems in different wavelength regions. We shall also make a first study of incorporating quantum dot gain and absorber material into optical Stark mode-locked lasers, aiming to exploit the intrinsically fast carrier dynamics of these structures. In summary, this proposal aims to shrink femtosecond technology from shoebox-size to credit-card size, and in the process explore a regime of ultrafast semiconductor dynamics that has never before now been exploited to produce light pulses.

Abstracts are not currently available in GtR for all funded research. This is normally because the abstract was not required at the time of proposal submission, but may be because it included sensitive information such as personal details.

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.

Optical fibre lasers offer significant benefits in comparison to other laser sources, such as extremely low thermal lensing, extraordinary good beam quality and very high plug efficiency. Optical fibre lasers have worldwide sales in excess of $300M and a predicted annual growth rate of 20-40%, thus are rapidly replacing other types of more conventional lasers. Indeed, the increasing deployment of high power fibre lasers in manufacturing has improved consumption efficiency. Up to date only near-IR sources have been manufactured in fiberized forms. The challenge is to develop new fiberized sources in the mid-UV. The successful manufacture of optical fibre lasers would have numerous applications which include, amongst others, water purification, insulators (such as plastics or glass) marking and processing, explosive detection, forensics and counter measures. This projects aim to demonstrate the possibility to use solid silica fibres to efficiently generate light in the UV. The proposed programme spans from the manufacture of specialty silica fibres transparent to the UV, doped with novel lasing elements, the design of fiberized laser pumps, and their combination in suitable systems to produce a new generation of affordable higher performance lasers. A variety of lasers with wavelength in the range 170nm to 330 nm will be developed and their applications in Raman spectroscopy and supercontinuum generation will be investigated.