Investigation on laser-plasma coupling in intense, ultrashort irradiation of a nanostructured silicon target

Year: 2014

Authors: Cristoforetti G., Anzalone A., Baffigi F., Bussolino G.C., D’Arrigo D., Fulgentini L., Giulietti A., Koester P., Labate L., Tudisco S., Gizzi LA.

Autors Affiliation: Intense Laser Irradiation Laboratory (ILIL), INO-CNR, Via G.Moruzzi 1, 56124 Pisa, Italy; INFN—Laboratori Nazionali del Sud, via S. Sofia 62, 95125 Catania, Italy; Istituto per la Microelettronica e Microsistemi, CNR, VIII strada 5, 95121 Catania, Italy; INFN, Pisa Section, Largo B. Pontecorvo 3, 56127 Pisa, Italy

Abstract: One of the most interesting research fields in laser–matter interaction studies is the investigation of effects and mechanisms produced by nano- or micro-structured targets, mainly devoted to the enhancing of laser–target or laser–plasma coupling. In intense and ultra-intense laser interaction regimes, the observed enhancement of x-ray plasma emission and/or hot electron conversion efficiency is explained by a variety of mechanisms depending on the dimensions and shape of the structures irradiated. In the present work, the attention is mainly focused on the lowering of the plasma formation threshold which is induced by the larger absorptivity.
Flat and nanostructured silicon targets were here irradiated with an ultrashort laser pulse, in the range 1 × 1017–2 × 1018 W µm2 cm−2. The effects of structures on laser–plasma coupling were investigated at different laser pulse polarizations, by utilizing x-ray yield and 3/2ω harmonics emission. While the measured enhancement of x-ray emission is negligible at intensities larger than 1018 W µm2 cm−2, due to the destruction of the structures by the amplified spontaneous emission (ASE) pre-pulse, a dramatic enhancement, strongly dependent on pulse polarization, was observed at intensities lower than ~3.5 × 1017 W µm2 cm−2. Relying on the three-halves harmonic emission and on the non-isotropic character of the x-ray yield, induced by the two-plasmon decay instability, the results are explained by the significant lowering of the plasma threshold produced by the nanostructures. In this view, the strong x-ray enhancement obtained by s-polarized pulses is produced by the interaction of the laser pulse with the preplasma, resulting from the interaction of the ASE pedestal with the nanostructures.

Journal/Review: PLASMA PHYSICS AND CONTROLLED FUSION

Volume: 56 (9)      Pages from: 095001  to: 095001

More Information: This work was carried out in the framework of the CNR High Field Photonics Unit (MD.P03.034). The authors acknowledge financial support from the CNR funded Italian research Network \’ELI-Italy (Attoseconds)\’ and from the PRIN project (contract no. PRIN2012AY5LEL). We also acknowledge contribution from the MIUR-FIRB project \’SPARX\’ (Sorgente Pulsata Auto-Amplificata di Radiazione X) and the INFN \’Plasma-med\’ collaboration. Petra Koester also acknowledges support from the Italian Ministry of Health through the project GR-2009-1608935.
KeyWords: laser-plasma interaction; ultrashort laser; nanostructured target; two-plasmon decay; hot-electron generation
DOI: 10.1088/0741-3335/56/9/095001

Citations: 37
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