Transient High Energy Density Plasmas Driven By Few Cycle Laser Pulses.

Lead Research Organisation: Imperial College London
Department Name: Physics

Abstract

The broad aim of this project is to provide high quality training of a PhD student, centred around the application of state of the art, few-cycle and OPCPA laser systems such as Astra-Artemis and the 10PW front-end at the Rutherford Appleton Laboratory (RAL) to the study of transient, high energy density plasmas. The scientific thrust of the programme is in response to the ability of new laser systems to deliver intense, sub-10-fs light pulses, and the exciting prospect of higher pulse energies, and variable wavelengths in the near future. Recent experimental work has shown that these ultra-fast light pulses can be used to create solid density plasmas with temperatures in the 100-200 eV range with unique spectral features such as strong suppression of emission lines via continuum lowering. This new observation, along with the very resent availability of a 10 fs beam line at RAL (provided via a collaboration with Imperial College) provides a timely opportunity to build UK expertise and supporting theoretical and computational capabilities in this emerging field.As part of this project the student will conduct high energy density plasma physics experiments at RAL and Imperial College. To date only open K-shell ions have been produced in low Z materials by few-cycle pulses in proof-of-principle experiments. As higher energies become available via access to planned new facilities at RAL the project will be extended to allow highly-transient open L- and M-shell ions to be produced and studied for the first time. A specific aim of this work will be to identify spectral markers of laser pre-pulse that can be used to benchmark the performance of future high-energy, few-cycle laser systems at RAL and elsewhere. In order to interpret spectroscopic data from these plasmas, the student will also development new numerical and computational tools which will be made available to the wider UK community via RAL. To address the experimental and theoretical aspects of the work the project will bring together the ultra-fast light source expertise of the Quantum Optics Group together with the extensive atomic physics and numerical modelling capabilities of Plasma Physics Group at Imperial College. The training opportunity afforded by this project will help strengthen the user base for high intensity laser facilities in the UK and thus help to ensure that the current world leading position in this field is maintained. It will also result in enhanced support for facility users by producing new numerical tools for modelling the atomic and spectroscopic plasmas at very high density. Finally, it will provide a student with the opportunity to train along side leading researchers and to provide them with the skills necessary to develop their own independent scientific programmes in the future.
 
Description We have shown how to apply new laser techniques in order to create and amplify light pulses only a few 10's of femtoseconds in duration, at very high repetition rate, and in a way that can be scaled up to high energies.

We used a technique called Optical Parametric Chirped Pulse Amplification to transfer energy from a high-energy but long duration "pump" laser pulse to an initially weak but very short duration (~7 femtosecond) seed pulse.

We showed how to manipulate the shape of the pump to give the most efficient energy transfer to the seed.

We also discovered that electronic synchronisation of pump and seed sources in complex OPA lasers can be extremely problematic, and that a more to all optical synchronisation system with a single front end laser source is far more robust.
Exploitation Route Laser sources of the kind we created are now being used to drive high intensity laser experiments at high repetition rate in University scale laboratories, that previously had to be conducted at major national facilities.

X-ray light sources driven by these new lasers have important potential applications in areas such as 3D tomographic medical imaging.
Techniques based on our work can be used to underpin new laser based light sources operating in the mid infra red where few if any suitable gain storage laser materials exist.
Sectors Aerospace, Defence and Marine,Energy,Healthcare,Manufacturing, including Industrial Biotechology,Security and Diplomacy
 
Description The primary aim of the project was advanced training of a young research scientist able to operate effectively within the demanding environment of National Facility scale laser systems. This was accomplished in part by development of high-level research skills in a University laboratory, and in part by participation in experiments at the Rutherford Appleton Laboratory. The researcher concerened (Dr Katalin Mecseki) has now taken up a staff position at a major laser and light source facility in the US (LCLS). Specific scientific outcomes include :- A better understanding of advanced optical parametric laser systems has emerged from this work. This have been used to determine how future higher energy very short pulse lasers could be constructed in a way that will avoid current technical limitations in hollow fibre pulse compression . The laser development has informed work on laser driven particle acceleration with the potential to create advanced x-ray light sources applicable to medical imaging.
First Year Of Impact 2013
Sector Aerospace, Defence and Marine,Healthcare
 
Description Controlled High-Repetition Plasma Based Electron Accelerators
Amount £746,000 (GBP)
Funding ID EP/H00601X/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 02/2010 
End 01/2014
 
Description MURI - MIR
Amount £2,050,049 (GBP)
Funding ID EP/N018680/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 12/2015 
End 11/2018
 
Title All optically synchronised few-cycle OPCPA laser system 
Description We developed a high repetition rate Optical Parametric Chirped Pulse Amplification (OPCPA) laser system in which the seed pulses for the short-pulse and OPA pump pulse are derived from a single 800nm few-cycle laser source. Wavelength shifting from 800nm to 1053nm in a photonic crystal fibre was used to allow seeding of the OPA pump chain directly from the few cycle oscillator. This allowed us to eliminate problematic high-frequency synchronisation electronics and move to a very robust all-optical synchronisation scheme. The laser system is now able to create few-cycle high-intensity light pulses for driving a broad range of experiments in areas including electron-acceleration, few-cycle mid-IR light sources and transient high-energy-density plasmas. 
Type Of Material Improvements to research infrastructure 
Year Produced 2013 
Provided To Others? Yes  
Impact A key development is the ability to deliver high repetition rate laser pulses at 100-1000 Hz to research groups previously confined to working at national laboratory scale facilities at very low shot rates of ~1 shot / minute. 
 
Title Regenerative pulse shaping 
Description We developed a new method of interactively shaping the shape of a high intensity laser pulse during amplification in a so-called regenerative amplifier based on the use of a low finesse etalon. We showed that numerically this technique appears to be impractical due to the apparent extreme sensitivity to etalon thickness and angle. In practice the softening of design constraints when operating in a Gaussian mode laser cavity makes the system very robust in operation. We employed this technique to create pseudo-flat-top laser pulses of a few picoseconds in duration well optimised to pumping optical parametric amplifiers. 
Type Of Material Improvements to research infrastructure 
Year Produced 2014 
Provided To Others? Yes  
Impact This technique allows for more stable and more efficient operation of optical parametric amplification in systems able to generate few cycle laser pulses. In follow on work we are now collaborating with colleagues who wish to use the resulting light source for (A) laser acceleration of electrons at high repetition rate and (B) generation of high-intensity mid-IR laser pulses. 
 
Description MURI Mid IR - Fundamental Strong-Field Interactions with Ultrafast, Mid-Infrared Lasers. 
Organisation Ohio State University
Department Department of Physics
Country United States 
Sector Academic/University 
PI Contribution The MURI project "Fundamental Strong-Field Interactions with Ultrafast, Mid-Infrared Lasers" is a UK-US programme to deveop and exploit new ultra-high power Mid IR lasers. It is co-funded by the US AFOR and UK Dstl.
Collaborator Contribution Ohio State is the lead US organisation in a multi institute collaboration. They will also provide collaborative access to laser systems and equipment for joint experiments.
Impact MURI Grant,
Start Year 2015