School of Physics & Astronomy

Prof. Dino Jaroszynski (Strathclyde) ● Wednesday, 06 November, 2:00 PM ● Boyd Orr Building, Room 407

Plasma photonics and particle acceleration using high power lasers

Plasma is the fourth state of matter and forms more than 99.9% of observable matter in the universe. It is a fascinating medium because it is quasi-neutral, and can support currents and electric and magnetic fields. Here we will discuss how high power lasers can exert forces on plasma to manipulate and fashion it into ultra-compact accelerators, radiation sources and unique structured dielectric media for controlling light.  We will examine how the “ponderomotive” force of an intense and ultra-short duration laser pulse displaces electrons to set up a space charge electrostatic field while more massive ions are not displaced and remain quasi-static. Displaced electrons oscillate locally to form a wake behind the laser pulse, much in the same way as a boat displaces water to create a wake. The plasma density wake has an ultra-high electrostatic field associated with displaced electrons, which can be several hundreds of gigavolts per meter. This is one thousand to ten thousand times higher than the accelerating fields in a conventional accelerator. The ultra-compact laser wakefield accelerator can also be used as a radiation source. In this talk we will discuss progress that has been in developing laser wakefield accelerators and their unique properties. As with conventional accelerators they have numerous applications. We will discuss our most recent results applying the laser wakefield accelerator, including demonstration of an ultra-compact coherent radiation source, application of the particle beams in radio-therapy and using these devices to create medical radio-isotopes for therapy and imaging. We will also show how they can be used as test facilities for particle physics detectors.

In the last part of the talk we will focus on how intercepting intense laser beams can be used to create robust time dependent plasma dielectric structures in 1D, 2D and 3D. These layered, rod like or crystalline structures can be fashioned into robust optical components for manipulating light with light, using plasma as the intermediate medium. Because of their time dependent they open up a fourth dimension and can act as a time boundary, in contrast to the usual space boundaries that we are used to in optics. We will discuss fascinating new results where we have observed birefringence and amplification of light using these time dependent media.

Prof. Deepak Kar (Uni. of Witwatersrand, Johannesburg, South Africa) ● Wednesday, 30 October, 2:00 PM ● Boyd Orr Building, Room 407

A new paradigm in dark matter searches in the colliders

The existence and nature of dark matter (DM) is one of the biggest challenges in physics. Confirmed by myriad astrophysical observations, no sign DM has been observed in direct or indirect detection experiments. Historically searches for DM in colliders have focused on Weakly Interacting Massive Particles, or so called WIMPs. The usual signature is a Standard Model particle on one side, balanced by the WIMP candidate, which being invisible, results in an imbalance of energy-momentum in the detector, termed as missing transverse momentum. No evidence for WIMPs has been seen despite extensive search programs in previous and current colliders. That necessitates a paradigm shift in ways we search for DM in colliders. Strongly interacting dark sector models have gained popularity, as they have extensive phenomenology and novel, albeit challenging experimental signatures. For the last few years, the author has been involved in such explorations, not only publishing the first semi-visible jets search result from ATLAS, but also involved in studies in model building and designing sensitive observables. In this talk, he will pedagogically introduce the models, show the current experimental results, and discuss the ongoing work in this area.