Optical Diagnostics of Colliding Laser Produced Plasmas Paddy Hayden National Centre for Plasma Science & Technology (NCPST)/ School of Physical Sciences, Dublin City University EMMI Workshop on Non-Linear Dynamics of Simple Quantum Systems at Extreme Temperatures and Intensities Nov 2 nd 2011

Outline Colliding Plasmas – Orientation Time Resolved Imaging Interferometry Visible Spectroscopy – Density – Temperature Ion Emission Summary EMMI NDSQS Workshop 2011

Colliding Plasmas - Orientation EMMI NDSQS Workshop 2011

Colliding Plasmas - Orientation EMMI NDSQS Workshop 2011 Multi-fluid colliding plasma simulations, Multi-fluid colliding plasma simulations, Rambo and Denavit, J. COMP. PHYS (1992) 0 time 150 timesteps300 timesteps When plasma plumes collide there are two extreme scenarios: 1. Interpenetration - interactions are mostly via binary collisions 2. Stagnation - plumes decelerated at collision plane, rapid accumulation of material, kinetic energy converted into excitation energy (glow), rapid growth of dense (stagnated) layer,………

Colliding Plasmas - Orientation The parameter which determines whether the plumes are likely to interpenetrate or stagnate is the so-called ‘collisionality parameter’ given by: Where D is the separation between the two plasmas and λ ii is the ion-ion Mean Free Path (MFP). EMMI NDSQS Workshop 2011

Controllable parameters: 1.Plasma Separation 2.Laser intensity 3.Target angle (0 o to 180 o ) 4.Laser wavelength/pulse duration. Colliding Plasmas - Orientation EMMI NDSQS Workshop 2011 From laterally colliding to counter streaming Key point: One can engineer stagnation layer characteristics; ‘hardness’, density, temperature, shape, etc. by varying geometry (D) and laser-target interaction physics (mfp, λ ii ) - application specific…..

EMMI NDSQS Workshop 2011 Time Resolved Imaging Resolution of ~4 ns (now 1.5 ns), use filters to isolate emission from a particular ion stage

Time Resolved Imaging EMMI NDSQS Workshop 2011 Seed Plasmas with 1.3 mm separation, each formed with 300 mJ, 1064 nm, 6 ns laser pulses. Spotsize: ca. 100 μm. Time delay measured relative to the peak of the split laser pulse.  t = 0 ns  t = 295 ns  t = 30 ns  t = 100 ns  t = 200 ns  t = 600 ns

Angle Resolved Imaging EMMI NDSQS Workshop 2011

Nomarski Interferometry EMMI NDSQS Workshop 2011

Comparison to Imaging

Visible Spectroscopy EMMI NDSQS Workshop 2011 Min. gate width ~4 ns Spatial Res. = 70 μm Spectral Res. = <0.2nm

Visible Spectroscopy EMMI NDSQS Workshop 2011 Target Wavelength (nm) Time-Space Density Measurements: Voigt profiles fitted and densities determined by Lorentzian width and Stark parameters in C. Colón et al. Phys. Scr. 73 (2006) 410–419. Delay = 300 ns

Visible Spectroscopy EMMI NDSQS Workshop 2011 Experimental Parameters used: 140 o wedge target, each seed plasma formed with 200 mJ, 1064 nm, 6 ns pulses. Spotsize: 100 μm, plasma separation: 2.6 mm. Time delay relative to peak of laser pulse. 100 o target

Visible Spectroscopy EMMI NDSQS Workshop 2011 Time-Space Temperature Measurements Target Wavelength (nm) Delay = 300 ns Temperatures from nm and nm Sn III lines. Spectrum is binned at 0.5 mm intervals. Temperatures were determined from the line ratios.

EMMI NDSQS Workshop 2011 Distance (mm) Visible Spectroscopy Experimental Parameters used: 140 o wedge target, each seed plasma was formed with 200 mJ, 1064 nm, 6 ns pulses. Spotsize: 100 μm and plasma separation: 2.6 mm. Time delay relative to peak of laser pulse. 100 o target

Ion Emission EMMI NDSQS Workshop 2011 Angle Resolved Ion Emission Experiment

Ion Emission EMMI NDSQS Workshop 2011 We observe quite significant narrowing of the TOF distribution compared to single plasma plumes Plasma ion bunch compression

Ion Emission EMMI NDSQS Workshop 2011 As we move the detector off normal emitted ion flux from each (left or right hand side) single plume dominates => weak lateral emission from stagnation layer -fewer damaging fast ions and perhaps less plasma debris?

Ion Emission EMMI NDSQS Workshop 2011 One can also tune the width and peak energy of the ‘total ion’ TOF distribution with the laser energy (6ns/1064nm)

Strong stagnation in table top colliding plasmas due to large value of the collisionality parameter (ζ) Degree of confinement/ hardness of the stagnation layer can be controlled by designing the value of ζ Stagnation layer becomes quite uniform after 100ns It looks attractive for investigation as alternative injector systems for ion accelerators, pulsed laser materials deposition source, LIBS, laboratory- astrophysical model experiments, X-ray lasers, fusion (Hohlraums) etc. Real time exploration of t and D to optimise stagnation layer conditions in an application specific manner. EMMI NDSQS Workshop 2011 Summary

EMMI NDSQS Workshop 2011 Acknowledgements DCU: J. Costello, P. Hough, J. Dardis, T. Kelly, C. Fallon and B. Doohan S. S. Harilal. School of Nuclear Engineering, Purdue University N. Gambino, University of Catania, Italy UCD: G. O’Sullivan, P. Dunne, E. Sokell, F. O’Reilly,... TCD: J. Lunney, I. Tobin Funding: Science Foundation Ireland 07/IN.1/I1771, Irish Research Council for Science Engineering and Technology (Embark Initiative), EU COST MP0601 Action and ERASMUS MUNDUS - EMJD -EXTATIC - FPA EACEA programme