The interaction of a sufficiently intense laser pulse with an initially solid target can result in the formation of a plasma in which surface electrons are accelerated to relativistic speeds on time scales shorter than a laser cycle. These electrons can form dense bunches and emit radiation that is upshifted in frequency relative to that of the incident laser pulse, reaching up to extreme-ultraviolet (XUV) or even X-ray photon energies [1,2]. As this process repeats periodically with the laser, this upshifted radiation is emitted in the form of high harmonics of the laser frequency. Here, we show clear experimental data demonstrating that this process can be controlled by converting part of the incident laser energy into its second harmonic before it is incident on the target surface. Fine tuning of the sub-cycle timing of this second harmonic pulse can significantly alter the shape of the incident waveform, which modifies the trajectories of the electrons, and can lead to a dramatic increase of the efficiency at which energy is converted into XUV radiation [3]. As well as providing insights into the relativistic dynamics of surface electrons in these interactions, this has the potential to lead to new laser based, coherent XUV sources with unprecedented pulse energies and even attosecond scale pulse durations.

[1] R. Lichters et al., Phys. Plasmas, 3, 3425 (1996)
[2] B. Dromey et al., Nature Physics, 2, 456 (2006)
[3] M. Yeung et al., Nature Photon. 11, 32 (2016)

In this talk we will review progress in developing laser-plasma based accelerators and radiation sources. These next-generation, ultra-compact devices have a niche potential for some applications, and could become widespread because of their lower cost and compactness when compared with conventional technology. The University of Strathclyde in Scotland has been driving forward a research programme, since 2000, to develop these novel technologies. Significant progress has been made towards controlling and characterising the beams from laser-plasma wakefield accelerators (LWFAs) since the first demonstration of controlled acceleration in 2004, which was published as one of the trio "Dream Beam" papers in Nature. Notably, acceleration of ultra-short duration bunches of electrons to 80-800 MeV has been demonstrated with percent-level energy spread, picocoulomb charge and 1 pi mm mrad emittance. The 10's of microns diameter LWFA "structure" traverses a few millimetres before dephasing. This results in an accelerator that is up to three orders of magnitude shorter than a conventional accelerator for the same energy. The dramatic reduction in size results in ultra-short electron bunches that are much shorter than from conventional accelerators. To determine the duration of the 1-10 pC bunches from the LWFA we have measured coherent transition radiation emitted as the bunches pass through a thin metal foil, and found it to be surprisingly short, approximately one femtosecond, which is two orders of magnitude shorter than bunches from most conventional accelerators. We will show how this can be reduced to around 200 attoseconds. A consequence of this is that the peak current can be up to 10 kA, even for modest charges. These bunches can be sued to produce XUV and X-ray radiation with pulse duration of the same order of magnitude. We will discuss the energy apportioning conundrum of where the laser energy delivered to the plasma ends up, which gives rise to some uprising conclusions. The plasma structures have very large fields, which can exceed 100 GV/m and drive transverse betatron motion of the accelerating electrons. This gives rise to wiggler-like hard x-ray radiation. We will discuss experiments carried out to observe femtosecond duration gamma-ray betatron emission, where photon energies of up to 7 MeV have been measured. The peak brilliances measured are similar to fourth generation synchrotron sources, but in a photon energy range that is not accessible to conventional light sources. Using ultra-short bunches the peak brilliance can be further enhanced. Finally, we will discuss several applications of these particle and radiation sources, such as compact FELs and ion-channel lasers, and medical applications including radiotherapy and imaging.

This talk will review recent research at Heriot-Watt in the area of frequency comb sources. A major emphasis will be the development of OPO frequency combs, which are uniquely tunable sources for optical spectroscopy and metrology. I will discuss some of the details of OPO comb stabilisation and subsequent metrology. Implementations of OPO combs in dual comb spectroscopy will be described, and also the deployment of a laser astrocomb on the 10-metre Southern African telescope (SALT). Finally I will discuss recent results achieving a 5-12μm femtosecond OPO using the new material OP-GaP.