Pump laser for TW laser system

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£400,105

Nov. 1, 2022

March 31, 2023

The John Adams Institute (JAI) is a centre of excellence for advanced accelerator science and technology, based at the University of Oxford, Royal Holloway University of London, and Imperial College London. An important theme within JAI's research is the development of advanced plasma accelerators. These exploit the huge electric fields developed within density waves driven by intense laser pulses (or particle bunches) as they propagate through plasma. Laser-driven plasma accelerators have generated electron bunches with energies equivalent to that obtained by accelerating them across nearly 10 billion volts in plasma accelerator stages only a few centimetres long. Plasma accelerators therefore offer the potential to drive compact sources of energetic particles, and by oscillating these particles with magnetic fields -- as is done in today's, stadium-sized synchrotron facilities -- they could generate very bright X-ray sources for use in science, medicine, and industry. In the longer term, plasma accelerators could be used in a new generation of high energy particle colliders.

The JAI programme on Laser Wakefield Accelerators (LWFAs) aims to tackle many of the key issues which need to be solved before their many promising applications can be realized. In Oxford, this work concentrates on developing an architecture for enabling high-energy plasma accelerators operating at high (kilohertz) repetition rates.

The first component of this architecture is the hydrodynamic optically-field-ionized (HOFI) plasma channel, which was developed at Oxford. These are free-standing, "indestructible" optical waveguides capable of channelling relativistically-intense laser pulses over metre-scale distances. As such, they are a key technology for providing the plasma "target" in future high-repetition-rate laser-plasma accelerators.

The second component is the multi-pulse LWFA (MP-LWFA) concept, also developed in Oxford. This new approach seeks to overcome a fundamental road-block in the application of LWFAs: the short pulse (less than one-ten-billionth of a second), high-energy (a few joules) Ti:sapphire lasers used today have very low wall-plug efficiency (< 0.1%), and are limited to operation at repetition rates of only a few pulses per second. In contrast, many near- or medium-term applications of LWFAs require the delivery of thousands of pulses per second; and longer-term applications, such as particle colliders, also require much higher wall-plug efficiency.

The essential idea of MP-LWFA is to drive the plasma wave with a train of low energy laser pulses, rather than with a single, high-energy pulse. Each pulse in the train excites a low amplitude plasma wave, and if the pulses are spaced by the wavelength of the plasma wave, then the plasma waves add coherently, causing the amplitude of the plasma wave to grow towards the back of the train. This new approach opens up LWFAs to novel, efficient laser technologies which cannot generate short pulses directly, but which can provide longer, high-energy pulses at high (kilohertz) repetition rates.

The current proposal comprises a request funds to replace a pump laser which lies at the heart of the terawatt laser system used extensively in the JAI plasma accelerator research programme. This pump laser is nearly 20 years old and the manufacturer will no longer service or repair it. If it were to fail we could not complete a large fraction of our research programme.