YOTTA - exploring routes to the ultimate intensity regime
The year 2010 marked 50 years since the invention of the laser and during this time lasers have undergone several major advances with far reaching impact on science and industrial/every-day applications. Historically each advance in laser performance (whether pulse duration, power or wavelength) was quickly followed by corresponding leaps in scientific progress. New regimes accessed with increasing intensity were
non-linear optics for Intensities I > 1012 Wcm-2
strong field physics for I > 1015 Wcm-2 and
relativistic plasma science I > 1018 Wcm-2.
Currently, the highest power lasers available are rated in Petawatt (1015 W) units but on the horizon (5-10 years) systems are being designed to operate at the Exawatt (1018 W) level with focused beam intensity exceeding 1024 Wcm-2 (Yotta = 1024). This latest step change will unlock the door to the next predicted regime encompassing the exotic, unexplored world of non-linear QED (Quantum Electro-Dynamics) where electric fields are sufficiently large that it becomes possible, for example, to create particles (electron-hole pairs) from the vacuum.
Along the way towards NL-QED we can identify three essential and so far unanswered questions.
1. How can we generate QED intensities? This is the key to NL-QED and we study a number of open questions in this area such as:
• What is the most promising route towards these high intensities?
• Can kilovolt photons generated by high harmonics generated from relativistically oscillating plasmas or from ultra-thin “flying mirror” targets be focused to relevant intensities?
• How can such harmonics be selected, enhanced and characterised?
2. Which effects of NL-QED can be measured? Theoretical work is focused on the onset of nonlinear QED effects, and to identify realistic experiments for detecting these effects. This includes the development of numerical codes to model strong field interaction with the vacuum, HHG in vacuum, photon-photon collisions, Unruh radiation etc. Based on these studies we investigate means to achieving feasible experiments. This includes:
• Can suitable tunable ion beams be generated from radiation pressure acceleration (RPA) techniques for electron-ion scattering experiments?
• Can GeV electron beams with <1% energy spread be produced from laser wakefield acceleration to study radiation loss and back-reaction effects?
• Can coherent X-ray sources be made useful for seeding XFELs which themselves are relevant to NL-QED effects?
3. How can NL-QED effects be measured? Along the way to achieving NL-QED experiments lie a number of technical challenges including:
• How to generate high quality vacuum conditions?
• How to measure spatial and temporal properties of ultra-intense X-ray pulses?
• How can optical laser energy be efficiently compressed/converted to HHG pulses?
• Can we develop OPCPA within our high power CPA laser system TARANIS (dual beam; each 20J/1ps) to access few cycle pulses as a method to reach ultra-high intensity?