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Enhancement of resonant absorption through excitation of SPR
Nuclear Instruments and Methods in Physics Research A ∎ (∎∎∎∎) ∎∎∎–∎∎∎
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Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Enhancement of resonant absorption through excitation of SPR Danilo Giulietti a, L. Calcagno e, Alessandro Curcio b,c, M. Cutroneo f, Mario Galletti b,n, J. Skala g, L. Torrisi d, M. Zimbone e a
Physics Department of the University and INFN, Pisa, Italy INFN – LNF, Via Enrico Fermi 40, 00044 Frascati, Italy c Sapienza – University of Rome, P.le Aldo Moro 2, 00185 Rome, Italy d Dipartimento di Fisica e SdT, Universitá di Messina, Messina, Italy e Dipartimento di Fisica ed Astronomia, Universitá di Catania, Italy f Nuclear Physics Institute, ASCR, 25068 Rez, Czech Republic g Institute of Physics, ASCR, v.v.i., 182 21 Prague 8, Czech Republic b
art ic l e i nf o
a b s t r a c t
Article history: Received 30 November 2015 Received in revised form 7 March 2016 Accepted 8 March 2016
In this experiment the absorption of the laser radiation impinging on polymeric films with Au nanoparticles implanted in surface was studied. By varying the polarization and the incidence angle of the laser radiation on target, the role in the laser absorption of both excitation of surface plasmons and excitation of electronic plasma waves at critical density through resonant absorption was highlighted. In conditions of p-polarized laser irradiations at 1015 W=cm2 intensity, resonant absorption can be induced in films enhancing proton and ion acceleration. Plasma on-line diagnostics is based on SiC detectors. Measurements of kinetic energy of accelerated ions indicate a significant increment using p-polarized laser light with respect to no-polarized light irradiation. & 2016 Published by Elsevier B.V.
Keywords: Laser–solid target interaction Nanoparticle implantation Surface plasmons Electronic plasma waves
1. Introduction High intensity laser–plasma interaction produces non-thermal equilibrium plasma in front of the laser irradiated target. A charge separation between the high mobility electrons, fast emitted, and the lower mobility ions, slowly emitted, occurs and a high electric field is developed for distances comparable with the Debye length depending on the electron temperature and density as below [1]: qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ð1Þ E ¼ ðne kT e Þ=ϵ0 where ϵ0 is the dielectric constant in vacuum, kTe the plasma electron temperature and ne the electron density. Thus the electric field increases with the plasma temperature and density. High intensity lasers interacting with matter produce ionizations in a time comparable to few laser cycles due to the interaction with the laser front tail, a pre-pulse, a pedestal or ASE. Fast electrons can be forward accelerated by longitudinal electric fields imposed by several different absorption mechanisms like resonant absorption for nanosecond laser pulses. Emitted ions are not isotropic because they follow the electron cloud, being driven and accelerated by the n
Corresponding author. E-mail address: [email protected] (M. Galletti).
developed electric field. After the fast electrons outgoing, the target becomes positively charged and ions are emitted. In the first instant of laser–matter interaction, different effects like reflection, transmission and scattering may occur giving rise to a decrement of the laser energy transfer to the plasma. In order to increase this transfer, the absorption coefficient of the laser radiation should be enhanced. Different procedures can be followed to increase the laser absorption in plasma, such as surface treatments, target shaping, doping of nanostructures in the thin foil or the use of peculiar irradiation conditions.
2. Laser absorption mechanisms A strong broad absorption band in the UV–visible wavelength range is observed in the extinction spectra of many metallic nanoparticles, such as Au and Ag, in water or when they are embedded in thin polymeric foils. This band is called surface plasmon resonance (SPR) and is due to the coupling of incident electromagnetic radiation into a surface plasmon, described as a collective oscillation of the conduction electrons, at the interface between the particle and the medium surrounding the particle [3]. The laser light induces an electric dipole on the nanoparticles with opposite electric field to the incident one. Due to the fact that the
http://dx.doi.org/10.1016/j.nima.2016.03.020 0168-9002/& 2016 Published by Elsevier B.V.
Please cite this article as: D. Giulietti, et al., Nuclear Instruments & Methods in Physics Research A (2016), http://dx.doi.org/10.1016/j. nima.2016.03.020i
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particle dimensions are smaller with respect to the laser wavelength, the induced field can be large enough to disruptively interfere with the laser, in such a way to produce important absorption effects. If the laser light has a frequency comparable with the plasma frequency of electrons oscillating on the nanoparticle surface the absorption becomes resonant. Media of high dielectric constants are effectively more polarizable and thus couple with the surface plasmon electrons more readily and the energy required to collectively excite the electrons is decreased. The use of nanoparticles embedded into polymers and resins allow preparing thin films to be irradiated with high intensity lasers. The high absorption coefficient of laser radiation produces hotter plasmas, both in forward and in backward directions, with emission of ions at higher energy with respect to the case of targets not containing metallic nanoparticles. Laser radiation obliquely incident on a plasma and with a component of the electric field in the plane of incidence can excite resonant longitudinal plasma oscillations at critical density surface nc [4]. The damping of the excited electron waves leads to conversion of electromagnetic laser energy into thermal energy. There is an optimum angle of incidence that maximizes the absorption effect. It can be shown that the resonance absorption coefficient is maximized at 50% for an angle of incidence given by sin ðθÞ 0:8ðωL L=cÞ 1=3 , where L is the density scale length, c the light velocity in vacuum, and ωL is the laser angular frequency. It is easy to show that s-polarized laser ! ! ! radiation, for which ∇ ne E ¼ 0, being ∇ ne the gradient of the ! electron density and E the electric field, cannot drive Langmuir waves, while it is possible for p-polarized radiation, for which ! ! ∇ ne E a 0; moreover in the p-polarization case the electron density perturbation of the plasma wave increases when the critical density is approached. On the base of this theory s and p laser irradiations of thin targets in high intensity laser–plasma interaction approach have been investigated at PALS laboratory in Prague in order to induce resonant absorption effects to study the consequent ion energy enhancement of the driven ion acceleration mechanism.
Fig. 1. Experimental set-up.
3. Experimental set-up The iodine laser radiation of PALS (λ ¼ 1315 nm; EL ¼ 400– 600 J; t ¼ 300 ps) was focused on targets at about 1015 W=cm2 in s or in p polarization incidence, through a quarter wave plate. The laser spot had a 70 μm diameter on the target surface, the incidence angle was 30 and the irradiations were performed in vacuum at a pressure of 10 6 mbar. Generally the irradiations were performed by focusing the laser at a distance of 100 μm in front of the target. The focal point (FP) was set in vacuum by micrometric step motors. At PALS the plasma diagnostics was based on different detectors: ion collectors (IC), SiC detectors. Details on the used diagnostics are given in literature [5,6]. We used two ICs, one is a ring IC (ICR) and it is positioned in forward direction at 0 and a 1.03 m distance from the target, another IC is positioned in backward direction at 30 and at 1.02 cm distance from the target. One SiC detector was placed in forward direction at 30 angle and at 60 cm distance from the target, another was placed in backward direction at 30 angle and at 64 cm from the target. IC and SiC detectors were employed in time-of-flight (TOF) configuration using a fast storage oscilloscope [2] (Figs. 1 and 2).
4. Results In the case of pure PVA using unpolarized laser, the signal intensity and the accelerated ion energy are very low, due to the
Fig. 2. Pure PVA, p-polarization laser.
low energy released by the laser in the thin film which is almost transparent. After the photopeak signal, used as a start signal for the TOF measurements, a large peak reveals the presence of ions of which protons are the fastest. The maximum proton kinetic energy is about 630 keV and the maximum yield, obtained for carbon ions, is of about 3 V. Irradiating pure PVA in p-polarization incidence the energy and the yield do not change significantly, increasing to about 700 keV and 5 V, respectively (Fig. 3). In films of PVA (polyvinylalcohol – C2H4On) containing metallic Au nanostructures, irradiated by unpolarized laser light, the SiC TOF signal/noise ratio is higher and ions more energetic with respect to the case of pure PVA. Due to the higher absorption coefficient, in this case, the maximum proton energy increases up to 1.2 MeV, while the faster heavier ions are carbons occurring at a kinetic energy of 6.3 MeV. Because the maximum charge state for carbon ions is C6þ , this energy corresponds to about 1.1 MeV/ charge state, in agreement with the energy measured for accelerated protons. The maximum ion yield, obtained for high ionized carbon ions, is about 20 V. The use of s-polarized laser incident both at 0 or at 30 does not change significantly the result obtained
Please cite this article as: D. Giulietti, et al., Nuclear Instruments & Methods in Physics Research A (2016), http://dx.doi.org/10.1016/j. nima.2016.03.020i
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Fig. 3. Pure PVA, no-polarization laser.
for unpolarized laser light irradiating pure PVA while for the PVAþAuNPs targets we can note the difference in the image below. In PVAþ Au nanostructures, irradiated in p-polarized mode the SiC TOF spectrum shows higher intensities and ion acceleration resulting from plasma wave excitation enhancing the laser energy transfer to the plasma. In this case the maximum proton energy corresponds to 1.9 MeV. Protons are followed by carbon ions occurring at 4:5 108 s, corresponding to a kinetic energy of 11.0 MeV. Because the maximum charge state for carbon ions is C6 þ, this energy corresponds to 1.9 MeV/charge state, in agreement with the energy measured for accelerated protons. The maximum ion yield, obtained for high ionized carbon ions, is about 50 V. Such experimental results have been confirmed also by the data collected with IC detectors placed all around the irradiated targets. Thus the obtained results indicate that the effect of high absorption results into an increment of the ion acceleration and of the ion field both using PVA pure and PVA drugged targets. We can note that we have a better enhancement with the second type of targets. The motivation is the major contribute on the process of the SPR effect (thanks to presence of nanoparticles) that superposes with PWER. Such experimental results have been confirmed also by the data collected with IC detectors placed all around the irradiated targets (Figs. 4 and 5).
Fig. 4. PVA with Au nanoparticles, s-polarization laser.
5. Conclusion and perspectives Surface plasmon resonances and plasma wave excitation resonance are two processes that can be used to enhance the laser absorption in plasmas and to increase the ion acceleration in laser irradiated thin foils, in high intensity laser–plasma interaction regime. In case of hydrogenated polymers, such as PVA, rich in low Z elements, the plasma density and the laser energy transfer to the target are low, due to the low absorption, in fact in thin (8 m) films the transmission of the order of 80% [7]. As a consequence high laser intensity generates non-equilibrium plasma in the rear side of the thin foil with a low electric field driving the ion acceleration. In this experiment a value of about 600–700 keV was obtained for the maximum proton energy in many irradiations. The insertion of AuNPs in the polymer, at concentration of 1% in weight, increases the effective Z equivalent of the target, increases the plasma temperature and electron density and induces high absorption effects. This effect enhances the laser absorption in the foil and an increment of the maximum proton energy up to about 1.2 MeV is obtainable. A further significant increment of the maximum proton energy was obtained using the increased absorption, due to the presence of AuNPs embedded in the polymer, over imposed to the PWER effect of plasma wave excitation due to the use of p
Fig. 5. PVA with Au nanoparticles, no-polarization laser (up) PVA with Au nanoparticles, p-polarization laser (down).
polarized laser light incident at 30 angle, i.e. in a way producing a longitudinal electric field orthogonal to the target surface. In such conditions, in fact, the laser absorption in plasma is maximized due to two resonance effects and as result the maximum proton acceleration energy increases up to about 1.9 MeV. This increment of a factor 3 times higher with respect to the irradiation of pure
Please cite this article as: D. Giulietti, et al., Nuclear Instruments & Methods in Physics Research A (2016), http://dx.doi.org/10.1016/j. nima.2016.03.020i
D. Giulietti et al. / Nuclear Instruments and Methods in Physics Research A ∎ (∎∎∎∎) ∎∎∎–∎∎∎
4
PVA polymer and a factor 16 higher in yield justify the use of advanced targets in order to promote the ion acceleration and the ion yield in many experiments of laser ion acceleration.
References [1] S. Eliezer, The interaction of high-power lasers with plasmas, Series in Plasma Physics, IOP Press, Bristol, 2002.
[2] M. Cutroneo, L. Torrisi, L. Calcagno, A. Torrisi, J. Phys.: Conf. Ser. 508 (2014) 012012 (pp. 1–7). [3] M.A. Garcia, J. Phys. D: Appl. Phys. 44 (2011) 283001 (pp. 1–20). [4] D. Giulietti, L.A. Gizzi, La Riv. Nuovo Cim. 21 (1) (1998) 1. [5] M. Cutroneo, P. Musumeci, M. Zimbone, L. Torrisi, F. La Via, D. Margarone, A. Velyhan, J. Ullschmied, L. Calcagno, J. Mater. Res. 28 (01) (2012) 87. [6] L. Torrisi, M. Cutroneo, L. Andò, J. Ullschmied, Phys. Plasmas 20 (2013) 023106. [7] Goodfellow, USA, Polymer Transmission Characteristics. Actual Website: 〈http://www.goodfellowusa.com/larger-quantities/polymers/tpx-character istics〉, 2014.
Please cite this article as: D. Giulietti, et al., Nuclear Instruments & Methods in Physics Research A (2016), http://dx.doi.org/10.1016/j. nima.2016.03.020i
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research A journal homepage: www.elsevier.com/locate/nima
Enhancement of resonant absorption through excitation of SPR Danilo Giulietti a, L. Calcagno e, Alessandro Curcio b,c, M. Cutroneo f, Mario Galletti b,n, J. Skala g, L. Torrisi d, M. Zimbone e a
Physics Department of the University and INFN, Pisa, Italy INFN – LNF, Via Enrico Fermi 40, 00044 Frascati, Italy c Sapienza – University of Rome, P.le Aldo Moro 2, 00185 Rome, Italy d Dipartimento di Fisica e SdT, Universitá di Messina, Messina, Italy e Dipartimento di Fisica ed Astronomia, Universitá di Catania, Italy f Nuclear Physics Institute, ASCR, 25068 Rez, Czech Republic g Institute of Physics, ASCR, v.v.i., 182 21 Prague 8, Czech Republic b
art ic l e i nf o
a b s t r a c t
Article history: Received 30 November 2015 Received in revised form 7 March 2016 Accepted 8 March 2016
In this experiment the absorption of the laser radiation impinging on polymeric films with Au nanoparticles implanted in surface was studied. By varying the polarization and the incidence angle of the laser radiation on target, the role in the laser absorption of both excitation of surface plasmons and excitation of electronic plasma waves at critical density through resonant absorption was highlighted. In conditions of p-polarized laser irradiations at 1015 W=cm2 intensity, resonant absorption can be induced in films enhancing proton and ion acceleration. Plasma on-line diagnostics is based on SiC detectors. Measurements of kinetic energy of accelerated ions indicate a significant increment using p-polarized laser light with respect to no-polarized light irradiation. & 2016 Published by Elsevier B.V.
Keywords: Laser–solid target interaction Nanoparticle implantation Surface plasmons Electronic plasma waves
1. Introduction High intensity laser–plasma interaction produces non-thermal equilibrium plasma in front of the laser irradiated target. A charge separation between the high mobility electrons, fast emitted, and the lower mobility ions, slowly emitted, occurs and a high electric field is developed for distances comparable with the Debye length depending on the electron temperature and density as below [1]: qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ð1Þ E ¼ ðne kT e Þ=ϵ0 where ϵ0 is the dielectric constant in vacuum, kTe the plasma electron temperature and ne the electron density. Thus the electric field increases with the plasma temperature and density. High intensity lasers interacting with matter produce ionizations in a time comparable to few laser cycles due to the interaction with the laser front tail, a pre-pulse, a pedestal or ASE. Fast electrons can be forward accelerated by longitudinal electric fields imposed by several different absorption mechanisms like resonant absorption for nanosecond laser pulses. Emitted ions are not isotropic because they follow the electron cloud, being driven and accelerated by the n
Corresponding author. E-mail address: [email protected] (M. Galletti).
developed electric field. After the fast electrons outgoing, the target becomes positively charged and ions are emitted. In the first instant of laser–matter interaction, different effects like reflection, transmission and scattering may occur giving rise to a decrement of the laser energy transfer to the plasma. In order to increase this transfer, the absorption coefficient of the laser radiation should be enhanced. Different procedures can be followed to increase the laser absorption in plasma, such as surface treatments, target shaping, doping of nanostructures in the thin foil or the use of peculiar irradiation conditions.
2. Laser absorption mechanisms A strong broad absorption band in the UV–visible wavelength range is observed in the extinction spectra of many metallic nanoparticles, such as Au and Ag, in water or when they are embedded in thin polymeric foils. This band is called surface plasmon resonance (SPR) and is due to the coupling of incident electromagnetic radiation into a surface plasmon, described as a collective oscillation of the conduction electrons, at the interface between the particle and the medium surrounding the particle [3]. The laser light induces an electric dipole on the nanoparticles with opposite electric field to the incident one. Due to the fact that the
http://dx.doi.org/10.1016/j.nima.2016.03.020 0168-9002/& 2016 Published by Elsevier B.V.
Please cite this article as: D. Giulietti, et al., Nuclear Instruments & Methods in Physics Research A (2016), http://dx.doi.org/10.1016/j. nima.2016.03.020i
D. Giulietti et al. / Nuclear Instruments and Methods in Physics Research A ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
particle dimensions are smaller with respect to the laser wavelength, the induced field can be large enough to disruptively interfere with the laser, in such a way to produce important absorption effects. If the laser light has a frequency comparable with the plasma frequency of electrons oscillating on the nanoparticle surface the absorption becomes resonant. Media of high dielectric constants are effectively more polarizable and thus couple with the surface plasmon electrons more readily and the energy required to collectively excite the electrons is decreased. The use of nanoparticles embedded into polymers and resins allow preparing thin films to be irradiated with high intensity lasers. The high absorption coefficient of laser radiation produces hotter plasmas, both in forward and in backward directions, with emission of ions at higher energy with respect to the case of targets not containing metallic nanoparticles. Laser radiation obliquely incident on a plasma and with a component of the electric field in the plane of incidence can excite resonant longitudinal plasma oscillations at critical density surface nc [4]. The damping of the excited electron waves leads to conversion of electromagnetic laser energy into thermal energy. There is an optimum angle of incidence that maximizes the absorption effect. It can be shown that the resonance absorption coefficient is maximized at 50% for an angle of incidence given by sin ðθÞ 0:8ðωL L=cÞ 1=3 , where L is the density scale length, c the light velocity in vacuum, and ωL is the laser angular frequency. It is easy to show that s-polarized laser ! ! ! radiation, for which ∇ ne E ¼ 0, being ∇ ne the gradient of the ! electron density and E the electric field, cannot drive Langmuir waves, while it is possible for p-polarized radiation, for which ! ! ∇ ne E a 0; moreover in the p-polarization case the electron density perturbation of the plasma wave increases when the critical density is approached. On the base of this theory s and p laser irradiations of thin targets in high intensity laser–plasma interaction approach have been investigated at PALS laboratory in Prague in order to induce resonant absorption effects to study the consequent ion energy enhancement of the driven ion acceleration mechanism.
Fig. 1. Experimental set-up.
3. Experimental set-up The iodine laser radiation of PALS (λ ¼ 1315 nm; EL ¼ 400– 600 J; t ¼ 300 ps) was focused on targets at about 1015 W=cm2 in s or in p polarization incidence, through a quarter wave plate. The laser spot had a 70 μm diameter on the target surface, the incidence angle was 30 and the irradiations were performed in vacuum at a pressure of 10 6 mbar. Generally the irradiations were performed by focusing the laser at a distance of 100 μm in front of the target. The focal point (FP) was set in vacuum by micrometric step motors. At PALS the plasma diagnostics was based on different detectors: ion collectors (IC), SiC detectors. Details on the used diagnostics are given in literature [5,6]. We used two ICs, one is a ring IC (ICR) and it is positioned in forward direction at 0 and a 1.03 m distance from the target, another IC is positioned in backward direction at 30 and at 1.02 cm distance from the target. One SiC detector was placed in forward direction at 30 angle and at 60 cm distance from the target, another was placed in backward direction at 30 angle and at 64 cm from the target. IC and SiC detectors were employed in time-of-flight (TOF) configuration using a fast storage oscilloscope [2] (Figs. 1 and 2).
4. Results In the case of pure PVA using unpolarized laser, the signal intensity and the accelerated ion energy are very low, due to the
Fig. 2. Pure PVA, p-polarization laser.
low energy released by the laser in the thin film which is almost transparent. After the photopeak signal, used as a start signal for the TOF measurements, a large peak reveals the presence of ions of which protons are the fastest. The maximum proton kinetic energy is about 630 keV and the maximum yield, obtained for carbon ions, is of about 3 V. Irradiating pure PVA in p-polarization incidence the energy and the yield do not change significantly, increasing to about 700 keV and 5 V, respectively (Fig. 3). In films of PVA (polyvinylalcohol – C2H4On) containing metallic Au nanostructures, irradiated by unpolarized laser light, the SiC TOF signal/noise ratio is higher and ions more energetic with respect to the case of pure PVA. Due to the higher absorption coefficient, in this case, the maximum proton energy increases up to 1.2 MeV, while the faster heavier ions are carbons occurring at a kinetic energy of 6.3 MeV. Because the maximum charge state for carbon ions is C6þ , this energy corresponds to about 1.1 MeV/ charge state, in agreement with the energy measured for accelerated protons. The maximum ion yield, obtained for high ionized carbon ions, is about 20 V. The use of s-polarized laser incident both at 0 or at 30 does not change significantly the result obtained
Please cite this article as: D. Giulietti, et al., Nuclear Instruments & Methods in Physics Research A (2016), http://dx.doi.org/10.1016/j. nima.2016.03.020i
D. Giulietti et al. / Nuclear Instruments and Methods in Physics Research A ∎ (∎∎∎∎) ∎∎∎–∎∎∎
3
Fig. 3. Pure PVA, no-polarization laser.
for unpolarized laser light irradiating pure PVA while for the PVAþAuNPs targets we can note the difference in the image below. In PVAþ Au nanostructures, irradiated in p-polarized mode the SiC TOF spectrum shows higher intensities and ion acceleration resulting from plasma wave excitation enhancing the laser energy transfer to the plasma. In this case the maximum proton energy corresponds to 1.9 MeV. Protons are followed by carbon ions occurring at 4:5 108 s, corresponding to a kinetic energy of 11.0 MeV. Because the maximum charge state for carbon ions is C6 þ, this energy corresponds to 1.9 MeV/charge state, in agreement with the energy measured for accelerated protons. The maximum ion yield, obtained for high ionized carbon ions, is about 50 V. Such experimental results have been confirmed also by the data collected with IC detectors placed all around the irradiated targets. Thus the obtained results indicate that the effect of high absorption results into an increment of the ion acceleration and of the ion field both using PVA pure and PVA drugged targets. We can note that we have a better enhancement with the second type of targets. The motivation is the major contribute on the process of the SPR effect (thanks to presence of nanoparticles) that superposes with PWER. Such experimental results have been confirmed also by the data collected with IC detectors placed all around the irradiated targets (Figs. 4 and 5).
Fig. 4. PVA with Au nanoparticles, s-polarization laser.
5. Conclusion and perspectives Surface plasmon resonances and plasma wave excitation resonance are two processes that can be used to enhance the laser absorption in plasmas and to increase the ion acceleration in laser irradiated thin foils, in high intensity laser–plasma interaction regime. In case of hydrogenated polymers, such as PVA, rich in low Z elements, the plasma density and the laser energy transfer to the target are low, due to the low absorption, in fact in thin (8 m) films the transmission of the order of 80% [7]. As a consequence high laser intensity generates non-equilibrium plasma in the rear side of the thin foil with a low electric field driving the ion acceleration. In this experiment a value of about 600–700 keV was obtained for the maximum proton energy in many irradiations. The insertion of AuNPs in the polymer, at concentration of 1% in weight, increases the effective Z equivalent of the target, increases the plasma temperature and electron density and induces high absorption effects. This effect enhances the laser absorption in the foil and an increment of the maximum proton energy up to about 1.2 MeV is obtainable. A further significant increment of the maximum proton energy was obtained using the increased absorption, due to the presence of AuNPs embedded in the polymer, over imposed to the PWER effect of plasma wave excitation due to the use of p
Fig. 5. PVA with Au nanoparticles, no-polarization laser (up) PVA with Au nanoparticles, p-polarization laser (down).
polarized laser light incident at 30 angle, i.e. in a way producing a longitudinal electric field orthogonal to the target surface. In such conditions, in fact, the laser absorption in plasma is maximized due to two resonance effects and as result the maximum proton acceleration energy increases up to about 1.9 MeV. This increment of a factor 3 times higher with respect to the irradiation of pure
Please cite this article as: D. Giulietti, et al., Nuclear Instruments & Methods in Physics Research A (2016), http://dx.doi.org/10.1016/j. nima.2016.03.020i
D. Giulietti et al. / Nuclear Instruments and Methods in Physics Research A ∎ (∎∎∎∎) ∎∎∎–∎∎∎
4
PVA polymer and a factor 16 higher in yield justify the use of advanced targets in order to promote the ion acceleration and the ion yield in many experiments of laser ion acceleration.
References [1] S. Eliezer, The interaction of high-power lasers with plasmas, Series in Plasma Physics, IOP Press, Bristol, 2002.
[2] M. Cutroneo, L. Torrisi, L. Calcagno, A. Torrisi, J. Phys.: Conf. Ser. 508 (2014) 012012 (pp. 1–7). [3] M.A. Garcia, J. Phys. D: Appl. Phys. 44 (2011) 283001 (pp. 1–20). [4] D. Giulietti, L.A. Gizzi, La Riv. Nuovo Cim. 21 (1) (1998) 1. [5] M. Cutroneo, P. Musumeci, M. Zimbone, L. Torrisi, F. La Via, D. Margarone, A. Velyhan, J. Ullschmied, L. Calcagno, J. Mater. Res. 28 (01) (2012) 87. [6] L. Torrisi, M. Cutroneo, L. Andò, J. Ullschmied, Phys. Plasmas 20 (2013) 023106. [7] Goodfellow, USA, Polymer Transmission Characteristics. Actual Website: 〈http://www.goodfellowusa.com/larger-quantities/polymers/tpx-character istics〉, 2014.
Please cite this article as: D. Giulietti, et al., Nuclear Instruments & Methods in Physics Research A (2016), http://dx.doi.org/10.1016/j. nima.2016.03.020i