Measurements of parametric instabilities at laser intensities relevant to strong shock
generation

Year: 2018

Authors: Cristoforetti G., Antonelli L., Atzeni S., Baffigi F., Barbato F., Batani D., Boutoux G., Colaitis A., Dostal J., Dudzak R., Juha L., Koester P., Marocchino A., Mancelli D., Nicolai Ph., Renner O., Santos J.J., Schiavi A., Skoric M.M., Smid M., Straka P., Gizzi LA.

Autors Affiliation: INO CNR, Intense Laser Irradiat Lab, I-56124 Pisa, Italy; Univ Roma La Sapienza, Dipartimento SBAI, I-00185 Rome, Italy; Empa Swiss Fed Labs Mat Sci & Technol, CH-8600 Dubendorf, Switzerland; Univ Bordeaux, CNRS, CEA, CELIA,UMR 5107, F-33405 Talence, France; Czech Acad Sci, Inst Plasma Phys, Prague 18200 8, Czech Republic; Czech Acad Sci, Inst Phys, Prague 18221 8, Czech Republic; Lab Nazl Frascati, I-00044 Rome, Italy; DIPC, Donostia San Sebastian 20018, Basque Country, Spain; Natl Inst Nat Sci, Tokyo 1050001, Japan.

Abstract: Parametric instabilities at laser intensities in the range (2–6)  1015 W/cm2 (438 nm, 250 ps, 100–300 J) have been investigated in planar geometry at the Prague Asterix Laser System facility via calorimetry and spectroscopy. The density scalelength of the plasma was varied by using an auxiliary pulse to form a preplasma before the arrival of the main laser beam and by changing the delay between the two pulses. Experimental data show that Stimulated Brillouin Scattering (SBS) is more effective than Stimulated Raman Scattering (SRS) in degrading laser-plasma coupling, therefore reducing the energy available for the generation of the shock wave. The level of the SBS backscatter and laser reflection is found to be in the range between 3% and 15% of the incident laser energy, while Backward SRS (BRS) reflectivity ranges between 0.02% and 0.2%, depending
on the delay between the pulses. Half-integer harmonic emission is observed and provides a signature of Two Plasmon Decay (TPD) occurring around the quarter of the critical density. Data analysis suggests that SRS is driven in beam speckles with high local intensity and occurs in bursts, particularly at higher laser intensities, due to the presence of kinetic mechanisms saturating the SRS growth in the speckles. Time-resolved measurements also show that BRS occurs in the trailing
part of the laser pulse, when the plasma has a longer density scalelength. Our measurements also indicate that hot electrons are predominantly produced by SRS rather than TPD.

Journal/Review: PHYSICS OF PLASMAS

Volume: 25      Pages from: 012702-1  to: 012702-12

More Information: Seventh Framework Programme, FP7, 284464. 257584. Ministero dell’Istruzione, dell’Universitŕ e della Ricerca, MIUR, 2012AY5LEL. College of Natural Resources, University of California Berkeley, CNR. LM2015083. EF16_013/0001552. Grantová Agentura Ceské Republiky, GACR, 17-05076S. CZ.02.1.01/0.0/0.0/15_008/0000162. CZ.02.1.01/0.0/0.0/15_003/0000449. – We would like to thank Professor S. Hueller for the fruitful discussions and valuable suggestions on the interpretation of Stimulated Raman Scattering data. We would like to acknowledge financial support from the LASERLAB-EUROPE Access to Research Infrastructure activity within the EC’s seventh Framework Program (Grant Agreement No. 284464).
KeyWords: shock ignition, laser-plasma interaction
DOI: 10.1063/1.5006021

Citations: 26
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