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Bacterial cells enhance laser driven ion acceleration.

Dalui M, Kundu M, Trivikram TM, Rajeev R, Ray K, Krishnamurthy M - Sci Rep (2014)

Bottom Line: Intense laser produced plasmas generate hot electrons which in turn leads to ion acceleration.Ability to generate faster ions or hotter electrons using the same laser parameters is one of the main outstanding paradigms in the intense laser-plasma physics.We envisage that the accelerated, high-energy carbon ions can be used as a source for multiple applications.

View Article: PubMed Central - PubMed

Affiliation: Tata Institute of Fundamental Research, 1 Homi Bhabha Road, Colaba, Mumbai 400 005, India.

ABSTRACT
Intense laser produced plasmas generate hot electrons which in turn leads to ion acceleration. Ability to generate faster ions or hotter electrons using the same laser parameters is one of the main outstanding paradigms in the intense laser-plasma physics. Here, we present a simple, albeit, unconventional target that succeeds in generating 700 keV carbon ions where conventional targets for the same laser parameters generate at most 40 keV. A few layers of micron sized bacteria coating on a polished surface increases the laser energy coupling and generates a hotter plasma which is more effective for the ion acceleration compared to the conventional polished targets. Particle-in-cell simulations show that micro-particle coated target are much more effective in ion acceleration as seen in the experiment. We envisage that the accelerated, high-energy carbon ions can be used as a source for multiple applications.

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Schematic of the experiment.A 800 nm, 50 fs laser pulse is focused, using an off-axis parabolic mirror, on the target. Inset shows the target surface geometry. Ions were detected using a Thomson parabola spectrometer at the target normal direction. dE and dB are the deflections of the charged particles due to the parallel electric and the magnetic field respectively. The TP was kept in a differentially pumped chamber maintained at a pressure of 10−7 torr, while the main experimental chamber was at 6 × 10−5 torr pressure.
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f1: Schematic of the experiment.A 800 nm, 50 fs laser pulse is focused, using an off-axis parabolic mirror, on the target. Inset shows the target surface geometry. Ions were detected using a Thomson parabola spectrometer at the target normal direction. dE and dB are the deflections of the charged particles due to the parallel electric and the magnetic field respectively. The TP was kept in a differentially pumped chamber maintained at a pressure of 10−7 torr, while the main experimental chamber was at 6 × 10−5 torr pressure.

Mentions: The experiment was performed using a Ti:Sapphire laser and the ions were detected at the target-front normal using a Thomson Parabola (TP) Spectrometer28 as shown in figure 1. The TP ion traces and the corresponding energy spectra for the carbon ions are shown in figure 2. The image shows that the dominant ions with the bacteria coated glass and the plain glass substrate are of carbon, oxygen and protons. Both the targets also show signal due to ions of higher atomic number (Z ~ 10). Carbon and oxygen have very close charge-to-mass ratios (q/m) and behave similarly. Oxygen ion energies are always found to show very similar behavior though the maximum ion energies are lower than the carbon ions. Thus, the acceleration features are summarized only with the analysis of carbon ions and other heavier ions are ignored in the present study. Protons on the other hand respond differently and its acceleration features are also presented in detail. Each ionic species, light or heavy, show a sharp cut-off towards the highest energy end in their respective kinetic energy spectra. This cut-off originates from the fact that the accelerated ions eventually catch up with the electrons, which inhibits further acceleration. Previous studies by Krishnamurthy et al, using the similar micro-particle system reported 70 fold enhancement in the hot electron production with 2.5 times increment in the hot electron temperature as compared to polished targets24. If we make a simple assumption that the 70 fold enhancement in the hot electron emission essentially correlates to an effective increase in the electron density, which increases the effective accelerating electrostatic sheath. Hence, the accelerating field is stronger by () (see equation 1) about 13 times. The maximum ion energy of the charge particles accelerated in such a sheath would be 13 times larger. We should keep in mind that, it is a very simplistic representation of a very complex phenomenon since the electron density is a strong function of both space and time and the dynamical evolution of the sheath with micro-particle structures can be very different. The simplistic picture, however, indicates that the maximum ion energy can be more than ten-fold larger if the ions are accelerated in such an enhanced electrostatic sheath field.


Bacterial cells enhance laser driven ion acceleration.

Dalui M, Kundu M, Trivikram TM, Rajeev R, Ray K, Krishnamurthy M - Sci Rep (2014)

Schematic of the experiment.A 800 nm, 50 fs laser pulse is focused, using an off-axis parabolic mirror, on the target. Inset shows the target surface geometry. Ions were detected using a Thomson parabola spectrometer at the target normal direction. dE and dB are the deflections of the charged particles due to the parallel electric and the magnetic field respectively. The TP was kept in a differentially pumped chamber maintained at a pressure of 10−7 torr, while the main experimental chamber was at 6 × 10−5 torr pressure.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4126001&req=5

f1: Schematic of the experiment.A 800 nm, 50 fs laser pulse is focused, using an off-axis parabolic mirror, on the target. Inset shows the target surface geometry. Ions were detected using a Thomson parabola spectrometer at the target normal direction. dE and dB are the deflections of the charged particles due to the parallel electric and the magnetic field respectively. The TP was kept in a differentially pumped chamber maintained at a pressure of 10−7 torr, while the main experimental chamber was at 6 × 10−5 torr pressure.
Mentions: The experiment was performed using a Ti:Sapphire laser and the ions were detected at the target-front normal using a Thomson Parabola (TP) Spectrometer28 as shown in figure 1. The TP ion traces and the corresponding energy spectra for the carbon ions are shown in figure 2. The image shows that the dominant ions with the bacteria coated glass and the plain glass substrate are of carbon, oxygen and protons. Both the targets also show signal due to ions of higher atomic number (Z ~ 10). Carbon and oxygen have very close charge-to-mass ratios (q/m) and behave similarly. Oxygen ion energies are always found to show very similar behavior though the maximum ion energies are lower than the carbon ions. Thus, the acceleration features are summarized only with the analysis of carbon ions and other heavier ions are ignored in the present study. Protons on the other hand respond differently and its acceleration features are also presented in detail. Each ionic species, light or heavy, show a sharp cut-off towards the highest energy end in their respective kinetic energy spectra. This cut-off originates from the fact that the accelerated ions eventually catch up with the electrons, which inhibits further acceleration. Previous studies by Krishnamurthy et al, using the similar micro-particle system reported 70 fold enhancement in the hot electron production with 2.5 times increment in the hot electron temperature as compared to polished targets24. If we make a simple assumption that the 70 fold enhancement in the hot electron emission essentially correlates to an effective increase in the electron density, which increases the effective accelerating electrostatic sheath. Hence, the accelerating field is stronger by () (see equation 1) about 13 times. The maximum ion energy of the charge particles accelerated in such a sheath would be 13 times larger. We should keep in mind that, it is a very simplistic representation of a very complex phenomenon since the electron density is a strong function of both space and time and the dynamical evolution of the sheath with micro-particle structures can be very different. The simplistic picture, however, indicates that the maximum ion energy can be more than ten-fold larger if the ions are accelerated in such an enhanced electrostatic sheath field.

Bottom Line: Intense laser produced plasmas generate hot electrons which in turn leads to ion acceleration.Ability to generate faster ions or hotter electrons using the same laser parameters is one of the main outstanding paradigms in the intense laser-plasma physics.We envisage that the accelerated, high-energy carbon ions can be used as a source for multiple applications.

View Article: PubMed Central - PubMed

Affiliation: Tata Institute of Fundamental Research, 1 Homi Bhabha Road, Colaba, Mumbai 400 005, India.

ABSTRACT
Intense laser produced plasmas generate hot electrons which in turn leads to ion acceleration. Ability to generate faster ions or hotter electrons using the same laser parameters is one of the main outstanding paradigms in the intense laser-plasma physics. Here, we present a simple, albeit, unconventional target that succeeds in generating 700 keV carbon ions where conventional targets for the same laser parameters generate at most 40 keV. A few layers of micron sized bacteria coating on a polished surface increases the laser energy coupling and generates a hotter plasma which is more effective for the ion acceleration compared to the conventional polished targets. Particle-in-cell simulations show that micro-particle coated target are much more effective in ion acceleration as seen in the experiment. We envisage that the accelerated, high-energy carbon ions can be used as a source for multiple applications.

Show MeSH