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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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PIC simulations.The proton energy spectra from the polished and ellipse coated target computed using particle-in-cell simulations. The enhanced sheath field formed with the micro-particle coating brings forth almost 10 fold increase in the maximum ion energy.
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f3: PIC simulations.The proton energy spectra from the polished and ellipse coated target computed using particle-in-cell simulations. The enhanced sheath field formed with the micro-particle coating brings forth almost 10 fold increase in the maximum ion energy.

Mentions: In the PIC simulation, E. coli bacteria are modelled as ellipsoidal micro-particles of size 0.7 μm × 1.8 μm to mimic the experimental target surface geometry. Thus, we consider two different kind of targets: (i) elliptical micro-particles distributed on a solid slab, and (ii) a plain solid slab (without micro-particles) which compares to the glass substrate. The chosen targets are then illuminated with a pulsed Gaussian light beam of wavelength λ = 800 nm. Numerical simulations are performed on a 1000 × 1000 rectangular grids with a uniform grid size of Δ = λ/40, and a time step of δt = Δ/2c (c is the speed of light) to have convergent solution and negligible numerical heating. The angle of incidence of the light pulse is controlled by rotating the target about an axis (y-axis) which is normal to the plane of incidence (x-z-plane, with z being the propagation and x being the polarization direction). In the simulation, the peak intensity, pulse width and the angle of incidence of the laser beam are taken as used in the experiment. Though the real target system has carbon, oxygen and protons, it is very difficult to simulate the exact target compositions in the PIC simulation as spatial variations of several species and their density distributions are not known exactly. We consider the target to be composed of only hydrogen (proton) for both the slab and the ellipsoidal micro-particles such that the essential differences in the ion acceleration with the change in the target features are deciphered. Since E. coli bacteria has more than 90% water content, we consider uniform initial electron density of 2nc for ellipsoidal particles, and 10nc for the solid slab (substrate) respectively, where, nc ≈ 1.72 × 1021 cm−3 is the critical electron density at a wavelength λ = 800 nm. Figure 3 shows the simulated proton energy spectra from the solid slab and the elliptical micro-particles coated solid slab. The result is plotted after the simulation is run for 66 fs. The simulation result very clearly demonstrates the generation of much higher energy ions with elliptical micro-particles or bacteria coated target compared to the plain solid slab target. The maximum ion energy is nearly ten times larger with the microstructured target much like the experimental measurements shown in figure 2c. The presence of the microstructure thus increases the laser energy absorption and the generation of hotter electrons. Enhanced hot electron generation in turn brings forward a stronger sheath electric field and facilitates with better ion acceleration.


Bacterial cells enhance laser driven ion acceleration.

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

PIC simulations.The proton energy spectra from the polished and ellipse coated target computed using particle-in-cell simulations. The enhanced sheath field formed with the micro-particle coating brings forth almost 10 fold increase in the maximum ion energy.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: PIC simulations.The proton energy spectra from the polished and ellipse coated target computed using particle-in-cell simulations. The enhanced sheath field formed with the micro-particle coating brings forth almost 10 fold increase in the maximum ion energy.
Mentions: In the PIC simulation, E. coli bacteria are modelled as ellipsoidal micro-particles of size 0.7 μm × 1.8 μm to mimic the experimental target surface geometry. Thus, we consider two different kind of targets: (i) elliptical micro-particles distributed on a solid slab, and (ii) a plain solid slab (without micro-particles) which compares to the glass substrate. The chosen targets are then illuminated with a pulsed Gaussian light beam of wavelength λ = 800 nm. Numerical simulations are performed on a 1000 × 1000 rectangular grids with a uniform grid size of Δ = λ/40, and a time step of δt = Δ/2c (c is the speed of light) to have convergent solution and negligible numerical heating. The angle of incidence of the light pulse is controlled by rotating the target about an axis (y-axis) which is normal to the plane of incidence (x-z-plane, with z being the propagation and x being the polarization direction). In the simulation, the peak intensity, pulse width and the angle of incidence of the laser beam are taken as used in the experiment. Though the real target system has carbon, oxygen and protons, it is very difficult to simulate the exact target compositions in the PIC simulation as spatial variations of several species and their density distributions are not known exactly. We consider the target to be composed of only hydrogen (proton) for both the slab and the ellipsoidal micro-particles such that the essential differences in the ion acceleration with the change in the target features are deciphered. Since E. coli bacteria has more than 90% water content, we consider uniform initial electron density of 2nc for ellipsoidal particles, and 10nc for the solid slab (substrate) respectively, where, nc ≈ 1.72 × 1021 cm−3 is the critical electron density at a wavelength λ = 800 nm. Figure 3 shows the simulated proton energy spectra from the solid slab and the elliptical micro-particles coated solid slab. The result is plotted after the simulation is run for 66 fs. The simulation result very clearly demonstrates the generation of much higher energy ions with elliptical micro-particles or bacteria coated target compared to the plain solid slab target. The maximum ion energy is nearly ten times larger with the microstructured target much like the experimental measurements shown in figure 2c. The presence of the microstructure thus increases the laser energy absorption and the generation of hotter electrons. Enhanced hot electron generation in turn brings forward a stronger sheath electric field and facilitates with better ion acceleration.

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