MURI - MIR

Lead Research Organisation: Imperial College London
Department Name: Dept of Physics

Abstract

For nearly a half century, investigations of a strong field laser-matter interaction have resulted in new fundamental discoveries and have fueled numerous applications. Historically, the advancement of strong field (SF) physics depended upon a symbiotic relationship between laser engineering and scientific discovery - new lasers enable science & applications while new discovery further drives innovative optical engineering. Although highly successful, present day laser technology has restricted the majority of SF studies to a narrow spectral window of visible & near infrared (NIR) wavelengths. This is now recognized as a consequential limitation, because over the last decade it has become clear that all SF phenomena benefit when they are driven at longer mid-infrared (MIR) wavelengths. At the present time we stand at a crossroad for discovery, where the road toward novel MIR technology can again transform SF physics, both our understanding of it and its applications. In fact, as presented in this proposal, increasing the wavelength is a faster, more robust path towards new physics than even increasing the intensity. The MURI MIR team will seize this opportunity with a broad in-depth research program aimed at advancing experiments, theory and technology for MIR SF interaction studies. In addition, our program is consciously constructed to directly connect these studies to DoD relevant applications in remote sensing, directed energy, tabletop coherent short wavelength light sources, compact particle accelerators and MIR laser technology.
Our team encompasses five linked thrust areas. Four of these thrusts focus on SF MIR science in fundamental ionization, filamentation in air, generation of coherent harmonic radiation and MIR driven ion & electron laser-plasma accelerators. The continuity of topics is anchored by foundational studies in simple systems and evolves across thrust areas to greater complexity. Recognizing lessons from the past, the fifth thrust is devoted to the development of novel MIR laser technology to advance our science thrust. The MURI MIR team is an alliance between 6 co-PIs in 5 US universities and 6 co-PIs at Imperial College in the UK. The team also forms key collaborative alliances with world leading laboratories. Overall there is balance in experiment & theory, complementary expertise, capabilities and educational value on both sides of the Atlantic. The team members are recognized leaders in MIR physics and as such bring competency & state-of-the-art MIR facilities to the program.

Planned Impact

The research will develop novel MIR sources, will train and influence cohorts of specific and associated postgraduate researchers, build and strengthen UK-US collaborations and those with European and Canadian laboratories.

Publications

10 25 50
 
Description Thrust 1 "Intense MIR Laser-Matter Interaction/Ionisation": The major achievements attained so far on experiments in this thrust are on the interaction of intense MIR fields with nanoscale matter (atomic clusters), molecules and towards pioneering work with liquids. In clusters we have reported the first observation of strongly laser field driven high kinetic energy electrons from the interaction of few-cycle 1.8 µm pulses focused to intensities of ~ 2 x 1014 Wcm-2 (Schutte et al, Scientific Reports (2016)). This result is of importance as it uncovers a mechanism for strong coupling of a long wavelength laser field to field ionised electrons that will underpin the early stages of the interaction for any nanostructured material or surface. We have also discovered in the course of this work a total electron yield dominating low energy electron emission mechanism that is again likely to be of general importance in laser-nanostructured matter interactions (in preparation for submission to PRL). We have used HHG emission to retrieve the nuclear and electronic dynamics for a range of organic molecule cations during the first few femtoseconds following ionisation in a strong mid-IR field (in preparation for submission to Nature Physics). In another development we are pioneering the study of the interaction of intense lasers fields with liquids, through the development of new technology to generate micron thickness, flat, stable liquid sheet jets (G.Galinis et al, Rev.Sci.Inst. (2017)). These jets are now being used in experiments on HHG and laser ion acceleration.
Averbukh and Ruberti (Imperial) have constructed a, first of its kind ab-initio, method for calculating the interaction of molecules with intense laser fields. This B spline ADC (algebraic diagrammatic construction) method can efficiently deal with the ionisation of a molecule in a MIR field (further details under Thrust 3).
Thrust 2 "Laser Propagation & Filamentation": Theory work on the role of excited states of molecules in pulse propagation and compression during filamentation has been conducted by Ivanov and co-workers (C.Bree et al, PRL (2018)). This topic is not a major focus of the UK programme but we anticipate new understanding emerging from our theory of molecular ionisation and the novel work on liquids.
Thrust 3 "High Harmonic Generation (HHG)": Our experiments are investigating the optimisation of soft X-ray attosecond pulses and the use of multi-colour coherent field synthesis to enhance the conversion efficiency in HHG. We have obtained, through our experiments and 3d numerical modelling, a deep understanding of the process of HHG generation driven by a few-cycle CEP stable MIR laser pulse that has confirmed that we can generate isolated attosecond pulses across the range from 150 - 600 eV. By making novel auxiliary time-resolved interferometry measurements we have proven that plasma defocusing is a dominant factor for MIR laser fields and from this we can better predict the best way to optimise yield (being resubmitted to Scientific Advances after a second round of favourable reviews). This source has already been used for XANES spectroscopy of a polymer (P3HT) at the S L and C K edges (Johnson et al, Structural Dynamics (2016)). Work has been progressing steadily on the infra-red field synthesiser based on the coherent addition of synchronised femtosecond pulses at different centre wavelengths to allow the generation of arbitrary pulsed fields, with special interest in the production of ultrashort transients. To date, we have successfully demonstrated the coherent addition of two pulses of different wavelengths (P. Matía-Hernando et al, Journal of Modern Optics (2017)) to synthesise a field which we subsequently used to generate sub-femtosecond high harmonic pulses in the vacuum-ultra-violet with improved pulse contrast. We were also able to make a complete electric-field characterisation of the synthesised field using an all-optical technique that we had developed previously.
The key theory avenues pursued were 1) the development of codes combining the static density functional treatment of material properties with electron dynamics induced by intense MIR laser fields, 2) high harmonic generation in strongly correlated materials and 3) HHG in novel polarization states. For strongly correlated materials, we showed how time-and-frequency resolved high harmonic light allows one to follow light-induced phase transition and breakdown of the strongly correlated insulating phase (Rui Silva et al, Nature Photonics, in press (2018)). Multi-color, intense MIR fields can convert fundamental radiation into coherent, circularly polarized soft X-ray light. Together with the MURI team of Murnane at the University of Colorado, we studied the properties of the scheme which uses non-collinear, counter-rotating fields for this purpose. We have predicted that strong parity-forbidden harmonics can be generated in this scheme (submitted to the New Journal of Physics, with another joint paper published in Optics Express (B.R.Galloway et al, OE (2016)). We have also developed a method to fully characterize the complete polarization state of attosecond pulses, including time-dependent ellipticity and partial polarization (A.Jimenez-Galan et al Nature Communications, accepted (2018)). Using the B spline ADC method we have successfully untangled the mechanism of multi-channel HHG in molecules (Ruberti et al, accepted PCCP) and have predicted the formation of bound coherent wave packets following MIR laser ionization (submitted PRL).
Thrust 4 "Laser-Particle Acceleration": MURI based laser Wakefield acceleration (LWFA) work has focused on modelling of upcoming experiments and in the meantime the multi-TW high power MIR sources needed for LWFA continue to be developed both at Imperial and at our MURI collaborators in the USA. We have work in preparation for publication on the multi-wavelength imaging capabilities of the CHIMERA laser as well as work on a novel electron injection mechanism based on rapid pump depletion. We took part in a first MIR LWFA commissioning run at ALLS in Montreal (MURI collaborators). Simulation work associated with this ongoing experimental work was presented at the European Advanced Accelerator Concepts Workshop in 2017.
The MURI grant has promoted significantly increased activity in ion acceleration with MIR lasers. MIR lasers allow the use of low-density gas targets which have advantages as a source for high energy laser generated ions, in terms of purity, repetition-rate, choice of ion species and improved beam parameters. In particular, MURI has allowed us to increase our experimental work on the 10 µm wavelength CO2 laser at the ATF, Brookhaven National Laboratory, which is the highest power CO2 laser in the world. ATF has recently implemented chirped pulse amplification (CPA) on a high-power CO2 laser for the first time, and this coupled with our enhancements in target shaping, has generated data clearly demonstrating the influence of radiation pressure effects in the acceleration of ions in low density targets. Particularly interesting is the measurement of higher energy gain in slightly longer scale-length plasmas, which can be attributed to the generation of a plasma grating structure, which is then accelerated by the radiation pressure of the intense pulse. These results are currently being prepared for publication.
Thrust 5 "Development of MIR Laser Technologies": We are developing an advanced few-femtosecond, high-energy, multi-wavelength "optical parametric amplification" (OPA) laser system that uses non-linear wavelength conversion rather than direct laser amplification as there are no suitable gain materials available in the MIR ("CHIMERA" laser). When completed it will be a unique platform for investigation MIR processes. To drive this system we have built a high-energy 1?m laser chain based on well understood diode and lamp pumped Nd:YLF technologies to boost and wavelength shift ~7fs pulses from a Ti:Sapphire oscillator. The aim now is to deliver >40mJ few-cycle laser pulses simultaneously at 3.2?m, 1.6?m and 0.8?m to allow us to investigate new MIR driven particle acceleration schemes. Given the complexity and ground breaking nature of the technical work we expect to see the majority of the scientific outputs that use this laser in the period 2018-2020. In a separate development we have partially completed an additional amplifier for our Ti:S CPA system that will be used to pump a further OPA stage to boost the available energy in our few-cycle hollow fiber 1.8 µm pulses with a target to increase this to 3-5 mJ.
Exploitation Route We anticipate our findings on: (a) new MIR laser technology, (b) intense MIR laser-matter interaction in atmospheric molecules, (c) intense MIR laser-matter interactions with nano-structures and liquids, (d) intense MIR laser acceleration (of both electrons and ions), to be of significant use to the broader research community as well as to the defence technology area. This research is ongoing.
Sectors Aerospace, Defence and Marine,Environment

 
Description EPSRC Standard Grant
Amount £1,200,000 (GBP)
Funding ID EP/R019509/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 06/2018 
End 05/2022
 
Title HHG based X-ray spectroscopy 
Description Development of sub-femtosecond coherent X-ray source based on HHG into the soft X-ray range (100 - 550 eV). First demonstration of recording static XANES in a polymer sample at the S L and C K edges, being developed as a time resolved technique. 
Type Of Material Improvements to research infrastructure 
Year Produced 2016 
Provided To Others? Yes  
Impact Too soon to tell - but very promising. 
 
Description ALLS 
Organisation National Institute of Scientific Research (INRS)
Country Canada 
Sector Academic/University 
PI Contribution Expertise in electron acceleration (Stuart Mangles, Jonathan Wood and team) to enabler joint experiments.
Collaborator Contribution Providing laser resources for experiment in form of a high power MIR system not currently available in UK.
Impact One experiment completed, new experiment planned.
Start Year 2016
 
Description Ohio State University (OSU) 
Organisation Ohio State University
Country United States 
Sector Academic/University 
PI Contribution We have developed a liquid sheet jet technology that will enable investigation of the interaction of intense MIR laser fields with liquids. We are investigating with our laser at 1.8 microns in collaboration.
Collaborator Contribution They are making available their 3 micron laser source for further investigation of the wavelength scaling.
Impact None yet
Start Year 2015