Limits...
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.


Energy spectra.Ion energy spectra for all the different ions obtained from the TPS images of both the nanoparticle (of 25 nm average size) coated target (left panel: a–c) and the polished Cu-substrate (right panel: d–f). Inset in a and d shows the corresponding SEM images of the targets. A 10 fold increment in the maximum carbon ion energy and an 8 fold increment in the maximum oxygen ion energy is observed with the nanoparticle coating compared to the polished bulk surface.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4495568&req=5

f3: Energy spectra.Ion energy spectra for all the different ions obtained from the TPS images of both the nanoparticle (of 25 nm average size) coated target (left panel: a–c) and the polished Cu-substrate (right panel: d–f). Inset in a and d shows the corresponding SEM images of the targets. A 10 fold increment in the maximum carbon ion energy and an 8 fold increment in the maximum oxygen ion energy is observed with the nanoparticle coating compared to the polished bulk surface.

Mentions: Ion emission measurements were carried out from the front surface of polished Cu-targets and compared each time with those from Cu-nanoparticle coated targets to understand the systematic variation in ion generation for mean particle sizes in the 7–25 nm range, as illustrated in figure 1. The ion emission from the target coated with a nanocrystalline Cu film with a mean particle size of 25 nm shows a rather drastic change compared to that from the polished bulk Cu-substrate. The laser energy coupling in this sample is enhanced significantly with respect to the polished Cu-substrate. Figure 2 shows the Thomson parabola ion traces from the nanoparticulate target and the polished Cu target. Cu-ions up to Cu3+ were observed from both the targets. A line cut of the image along the dotted line shows the well resolved ion peaks. Figure 3 shows the ion energy spectra obtained by analyzing Cuq+, H+, Cq+ and Oq+ ion traces of the TPS image22. For all the ions, the maximum energy is found to be significantly larger from the nanoparticulate target than from the reference. For instance, the maximum proton energy in the reference is ≈100 keV, whereas it is almost 200 keV from the 25 nm nanoparticle coated target, implying a two-fold increase in the proton acceleration. The proton flux in the energy range 25–100 keV is also about 1.5 times higher in the nanoparticulate target, but the Cu-ion flux is slightly lower than that of the reference Cu-substrate. The most significant enhancement in the acceleration occurs in the case of the carbon ions. Figure 3b,e show the carbon ion energy spectra from the 25 nm nanoparticle-coated target and the polished Cu target, respectively. The highest cut-off energy for C2+ and C3+ are 700 keV and 950 keV respectively from the nanoparticulate target, whereas, the highest detected carbon ion energy from the bulk Cu-substrate is only about 90 keV. Thus, coating the bulk Cu target with a layer of nanoparticles with an average size of 25 nm is found to provide more than 10-fold enhancement in carbon ion acceleration. Oxygen ions also exhibit similar acceleration features (8 fold enhancement in the maximum ion energy compared to the bulk), as shown in figure 3c,f. The highest observed oxygen ion energy is however less than that of the carbon ions for the same targets (nanoparticulate and polished).


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)

Energy spectra.Ion energy spectra for all the different ions obtained from the TPS images of both the nanoparticle (of 25 nm average size) coated target (left panel: a–c) and the polished Cu-substrate (right panel: d–f). Inset in a and d shows the corresponding SEM images of the targets. A 10 fold increment in the maximum carbon ion energy and an 8 fold increment in the maximum oxygen ion energy is observed with the nanoparticle coating compared to the polished bulk surface.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: Energy spectra.Ion energy spectra for all the different ions obtained from the TPS images of both the nanoparticle (of 25 nm average size) coated target (left panel: a–c) and the polished Cu-substrate (right panel: d–f). Inset in a and d shows the corresponding SEM images of the targets. A 10 fold increment in the maximum carbon ion energy and an 8 fold increment in the maximum oxygen ion energy is observed with the nanoparticle coating compared to the polished bulk surface.
Mentions: Ion emission measurements were carried out from the front surface of polished Cu-targets and compared each time with those from Cu-nanoparticle coated targets to understand the systematic variation in ion generation for mean particle sizes in the 7–25 nm range, as illustrated in figure 1. The ion emission from the target coated with a nanocrystalline Cu film with a mean particle size of 25 nm shows a rather drastic change compared to that from the polished bulk Cu-substrate. The laser energy coupling in this sample is enhanced significantly with respect to the polished Cu-substrate. Figure 2 shows the Thomson parabola ion traces from the nanoparticulate target and the polished Cu target. Cu-ions up to Cu3+ were observed from both the targets. A line cut of the image along the dotted line shows the well resolved ion peaks. Figure 3 shows the ion energy spectra obtained by analyzing Cuq+, H+, Cq+ and Oq+ ion traces of the TPS image22. For all the ions, the maximum energy is found to be significantly larger from the nanoparticulate target than from the reference. For instance, the maximum proton energy in the reference is ≈100 keV, whereas it is almost 200 keV from the 25 nm nanoparticle coated target, implying a two-fold increase in the proton acceleration. The proton flux in the energy range 25–100 keV is also about 1.5 times higher in the nanoparticulate target, but the Cu-ion flux is slightly lower than that of the reference Cu-substrate. The most significant enhancement in the acceleration occurs in the case of the carbon ions. Figure 3b,e show the carbon ion energy spectra from the 25 nm nanoparticle-coated target and the polished Cu target, respectively. The highest cut-off energy for C2+ and C3+ are 700 keV and 950 keV respectively from the nanoparticulate target, whereas, the highest detected carbon ion energy from the bulk Cu-substrate is only about 90 keV. Thus, coating the bulk Cu target with a layer of nanoparticles with an average size of 25 nm is found to provide more than 10-fold enhancement in carbon ion acceleration. Oxygen ions also exhibit similar acceleration features (8 fold enhancement in the maximum ion energy compared to the bulk), as shown in figure 3c,f. The highest observed oxygen ion energy is however less than that of the carbon ions for the same targets (nanoparticulate and polished).

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.