Plasmas created by extreme ultraviolet lasers

Lead Research Organisation: University of York
Department Name: Physics


The invention of the laser in the early 1960s led to experiments where high power (> million Watts) infra-red and visible pulsed lasers were focused onto solid targets in order to produce hot (> 0.5 million degrees Kelvin) plasmas. In almost 50 years of study, the physics of the laser interaction, the physics of the expanding plume and many important applications have been elucidated in some detail. When focussed onto solid targets, visible/infra-red lasers do not penetrate to the solid for most of the pulse duration, but are absorbed in the expanding plasma plume at densities 100- 1000 times smaller than the solid density. Dropping the laser wavelength into the extreme ultra-violet (EUV), however, enables the laser to penetrate into the solid and to create plasma directly at the solid density. Initial modelling studies that have been undertaken by the PI show that the interaction of EUV laser radiation with most solid targets will cause a rapid drop in opacity (so that the target 'bleaches'). Initially an attenuation length for the EUV photon energy is bleached and then another attenuation length, so that a 'bleaching wave' propagates through the solid target on a sub-nanosecond timescale. A much more massive amount of target material is effectively ablated than can occur with infra-red or visible radiation of the same pulse energy and focal spot diameter. Little modelling work has been undertaken to elucidate understanding of EUV laser-produced plasmas because of the lack of sufficiently energetic (> 10 microJoules) laboratory EUV lasers for experiments. However, reliable capillary discharge lasers operating at wavelength 46.9 nm (photon energy 26.4 eV) producing up to 1 milliJoule/pulse and peak powers of a million Watts have been developed at the Colorado State University (CSU). We propose to develop simulation models to interpret emission spectra and mass spectrometer results from EUV laser produced plasmas. We will test spectrometer diagnostics using the University of York high power infra-red laser and in collaboration with CSU make spectral and mass spectrometer measurements for comparison to the simulation models. A new class of laser-produced plasma will be studied with potential impact in the study of warm dense matter, laser cutting and ablation and solid material lithography with relevance to the $70B p.a. revenue industry associated with the manufacture of microelectromechanical systems (MEMS).

Planned Impact

A new class of extreme ultra-violet (EUV) laser-produced plasma will be studied with potential impact on the study of warm dense matter, ions for particle accelerators, laser cutting and ablation and solid material lithography. Many of the academic beneficiaries can be expected to carry over into impact. The impact of successful ICF would have a massive effect on the world economy. The use of EUV lasers for MEMS and micro-sampling may become a niche component of the $300B annual revenue associated with semiconductor industries and the $70B annual revenue associated with MEMS (which includes ink jet printer cartridges, car airbag systems and display systems). We plan to employ the York Plasma Institute Industry Officer for 10% of their time under this grant to develop ties to industries so as to maximise the research impact in MEMS and plasma coating. There are significant training impacts to this work. A student now in-post (1st year) supported by EPSRC and by AWE will work on this grant, with the expectation that a minimum of another student will commence work in the area. The requested pdra will receive training in fluid and collisional-radiative simulations of materials far from equilibrium, in the modelling of expanding laser-plasma plumes and in the technologically relevant aspects of this work.


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Description The research has shown that narrow features can be ablated with extreme ultra violet (EUV) lasers, with potential for impact in the ablation of micro-features in solid target. Free electron degeneracy effects have been shown to be important in modeling the interaction of EUV lasers with solids. The work has also led to a developed proposal for research on the use of the EUV laser in imaging high density laser-produced plasmas as used as EUV sources in EUV lithography.
Exploitation Route A method of focusing EUV laser light to sub-micron diameter needs to be developed. The use of Schwarzchild focusing optics is under development. Using the EUV laser for imaging of laser-plasmas is being undertaken with relevance to EUV source optimisation in EUV lithography as being used for the production of the next generation of semiconductors for computers and mobile phones.
Sectors Aerospace, Defence and Marine,Manufacturing, including Industrial Biotechology,Security and Diplomacy

Description The theoretical and modeling research on the physics of extreme ultra-violet (EUV) lasers has led to an increased understanding of collisional and radiative processes in dense plasmas which has led to revised treatments of these processes in cool, dense plasmas such as those produced in x-ray free electron laser interactions, dwarf stars and inertial fusion research. Rate coefficient treatments taking account of the degeneracy of free electron in dense plasmas were developed so that a 'correction' to the rate coefficient allowing for degeneracy can be implemented. The revised treatment is now being included in inertial fusion codes and collisional radiative codes modeling x-ray free electron interactions. The work has also lead to investigations as to the feasibility of using an extreme ultra-violet (EUV) laser to ablate micro-features in solids. An EUV capillary laser has been purchased and commissioned at the Unversity of York for this work. The EUV laser is also being investigated as an imaging tool of the laser-plasma sources used to produce the EUV for EUV lithography.
First Year Of Impact 2019
Sector Aerospace, Defence and Marine,Energy,Manufacturing, including Industrial Biotechology,Security and Diplomacy
Impact Types Cultural,Economic

Description AWE
Amount £70,000 (GBP)
Funding ID R13132 
Organisation Atomic Weapons Establishment 
Sector Private
Country United Kingdom
Start 10/2012 
End 09/2016
Description Diffraction model to simulate the focal spot of an EUV laser, focused by mirrors or a Fresnel Zone Plate. Efficiently parallelized for multiple processors. Well benchmarked against high intensity experimental results and published. 
Type Of Material Computer model/algorithm 
Provided To Others? No  
Impact Publication in Physical Review Applied Photonics. Used as an input to design future experiments. 
Description Extreme ultra-violet laser ablation of solids 
Organisation Colorado State University
Country United States 
Sector Academic/University 
PI Contribution The University of York have undertaken simulations of the interaction of extreme ultra-violet radiation with solid targets with a view to understanding the warm dense matter created by the interaction and in order to investigate the ablation/cutting of micro-features in solids.
Collaborator Contribution Colorado State University have supplied expertise in the running and use of a capillary discharge laser operating at 46.9 nm. They are also sourcing some focusing optics for an investigation of micro-ablation of solids.
Impact Ablation and transmission of thin solid targets irradiated by intense extreme ultraviolet laser radiation. / Aslanyan, Valentin; Kuznetsov, I; Bravo, H.; Woolston, M. R.; Rossall, Andrew Keith; Menoni, C. S.; Rocca, J. J.; Tallents, Gregory John. In: APL Photonics, 12.07.2016, p. 066101-1 - 066101-9.
Start Year 2016