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Preferential enhancement of laser-driven carbon ion acceleration from optimized nanostructured surfaces.

Dalui M, Wang WM, Trivikram TM, Sarkar S, Sarkar S, Tata S, Jha J, Ayyub P, Sheng ZM, Krishnamurthy M - Sci Rep (2015)

Bottom Line: However, particles smaller than 20 nm have an adverse effect on the ion acceleration.Particle-in-cell simulations provide definite pointers regarding the size of nanoparticles necessary for maximizing the ion acceleration.The inherent contrast of the laser pulse is found to play an important role in the species selective ion acceleration.

View Article: PubMed Central - PubMed

Affiliation: Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005, India.

ABSTRACT
High-intensity ultrashort laser pulses focused on metal targets readily generate hot dense plasmas which accelerate ions efficiently and can pave way to compact table-top accelerators. Laser-driven ion acceleration studies predominantly focus on protons, which experience the maximum acceleration owing to their highest charge-to-mass ratio. The possibility of tailoring such schemes for the preferential acceleration of a particular ion species is very much desired but has hardly been explored. Here, we present an experimental demonstration of how the nanostructuring of a copper target can be optimized for enhanced carbon ion acceleration over protons or Cu-ions. Specifically, a thin (≈ 0.25 μm) layer of 25-30 nm diameter Cu nanoparticles, sputter-deposited on a polished Cu-substrate, enhances the carbon ion energy by about 10-fold at a laser intensity of 1.2 × 10(18)  W/cm(2). However, particles smaller than 20 nm have an adverse effect on the ion acceleration. Particle-in-cell simulations provide definite pointers regarding the size of nanoparticles necessary for maximizing the ion acceleration. The inherent contrast of the laser pulse is found to play an important role in the species selective ion acceleration.

No MeSH data available.


Ion yield.Total ion yield from the nanoparticle (of different sizes) coated targets. The size of the particles are labelled accordingly.
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f5: Ion yield.Total ion yield from the nanoparticle (of different sizes) coated targets. The size of the particles are labelled accordingly.

Mentions: Interestingly, the nanoparticle-coated targets with relatively smaller particles (average size ≈ 7 nm and 15 nm) yielded negligible ion acceleration compared to the polished Cu-target. Figure 4 shows the kinetic energy spectra of the Cu-ions from the 7 nm and 15 nm sized nanoparticle coated targets. Irradiation on the 7 nm particle coated target yields up to doubly charged states of Cu-ions with energies in the range 3–20 keV. Although, Cu3+ ions are detected from the 15 nm particles coated target, the ion acceleration does not improve appreciably. No protons or the carbon ions are detected in the TPS from either the 7 nm or 15 nm particles. The TPS has a low energy cut-off determined by the applied electric field and deflects lower energy ions out of the detector. The absence of protons or carbon ions indicate that their energies are lower than the TPS cut-off energy, which is ≈3 keV in this particular configuration. Very low energetic ion emission from smaller nanoparticle (SNP: <20 nm) coated targets could be either because of longer plasma expansion into the vacuum or ablation of such tiny structures by the pre-pulse or both. SNPs are found to absorb the low intensity light much more efficiently than the larger sized nanoparticles (LNP: >20 nm). Since the melting temperature decreases with decreasing size23, the pre-pulse which is about 10−6 times intense compared to the main pulse, significantly affects SNP (than LNP) and generates a larger pre-plasma which affects the ion acceleration. Figure 5 shows the variation of the total ion yield with the size of the coated nanoparticles. With increasing nanoparticle size from 7 nm to 25 nm, the total ion yield increases systematically, a trend that is confirmed by the PIC simulations.


Preferential enhancement of laser-driven carbon ion acceleration from optimized nanostructured surfaces.

Dalui M, Wang WM, Trivikram TM, Sarkar S, Sarkar S, Tata S, Jha J, Ayyub P, Sheng ZM, Krishnamurthy M - Sci Rep (2015)

Ion yield.Total ion yield from the nanoparticle (of different sizes) coated targets. The size of the particles are labelled accordingly.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4495568&req=5

f5: Ion yield.Total ion yield from the nanoparticle (of different sizes) coated targets. The size of the particles are labelled accordingly.
Mentions: Interestingly, the nanoparticle-coated targets with relatively smaller particles (average size ≈ 7 nm and 15 nm) yielded negligible ion acceleration compared to the polished Cu-target. Figure 4 shows the kinetic energy spectra of the Cu-ions from the 7 nm and 15 nm sized nanoparticle coated targets. Irradiation on the 7 nm particle coated target yields up to doubly charged states of Cu-ions with energies in the range 3–20 keV. Although, Cu3+ ions are detected from the 15 nm particles coated target, the ion acceleration does not improve appreciably. No protons or the carbon ions are detected in the TPS from either the 7 nm or 15 nm particles. The TPS has a low energy cut-off determined by the applied electric field and deflects lower energy ions out of the detector. The absence of protons or carbon ions indicate that their energies are lower than the TPS cut-off energy, which is ≈3 keV in this particular configuration. Very low energetic ion emission from smaller nanoparticle (SNP: <20 nm) coated targets could be either because of longer plasma expansion into the vacuum or ablation of such tiny structures by the pre-pulse or both. SNPs are found to absorb the low intensity light much more efficiently than the larger sized nanoparticles (LNP: >20 nm). Since the melting temperature decreases with decreasing size23, the pre-pulse which is about 10−6 times intense compared to the main pulse, significantly affects SNP (than LNP) and generates a larger pre-plasma which affects the ion acceleration. Figure 5 shows the variation of the total ion yield with the size of the coated nanoparticles. With increasing nanoparticle size from 7 nm to 25 nm, the total ion yield increases systematically, a trend that is confirmed by the PIC simulations.

Bottom Line: However, particles smaller than 20 nm have an adverse effect on the ion acceleration.Particle-in-cell simulations provide definite pointers regarding the size of nanoparticles necessary for maximizing the ion acceleration.The inherent contrast of the laser pulse is found to play an important role in the species selective ion acceleration.

View Article: PubMed Central - PubMed

Affiliation: Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005, India.

ABSTRACT
High-intensity ultrashort laser pulses focused on metal targets readily generate hot dense plasmas which accelerate ions efficiently and can pave way to compact table-top accelerators. Laser-driven ion acceleration studies predominantly focus on protons, which experience the maximum acceleration owing to their highest charge-to-mass ratio. The possibility of tailoring such schemes for the preferential acceleration of a particular ion species is very much desired but has hardly been explored. Here, we present an experimental demonstration of how the nanostructuring of a copper target can be optimized for enhanced carbon ion acceleration over protons or Cu-ions. Specifically, a thin (≈ 0.25 μm) layer of 25-30 nm diameter Cu nanoparticles, sputter-deposited on a polished Cu-substrate, enhances the carbon ion energy by about 10-fold at a laser intensity of 1.2 × 10(18)  W/cm(2). However, particles smaller than 20 nm have an adverse effect on the ion acceleration. Particle-in-cell simulations provide definite pointers regarding the size of nanoparticles necessary for maximizing the ion acceleration. The inherent contrast of the laser pulse is found to play an important role in the species selective ion acceleration.

No MeSH data available.