On the effect of rear-surface dielectric coatings on laser-driven proton acceleration

Abstract

Laser-driven ion acceleration has been experimentally investigated by irradiating, with tightly focused femtosecond laser pulses at 5 x 10(19) W/cm(2), thin metal foils, which have been back-coated with a mu m thick dielectric layer. The observation we report shows the production of MeV proton bunches with an unexpected highly uniform spatial cross section. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3251425

Effect of resistivity gradient on laser-driven electron transport and ion acceleration

“…This results in a more uniform sheath field formed by the fast electrons at the target backside and leads to a much smoother transverse ion beam profile (compared to that of the uncoated target), thus contributing to the superior imaging quality of the proton beams accelerated off the coated Al targets. 23,24 …”

“…Recently, hybrid and particle-in-cell (PIC) methods have been used to study resistivity effects on the behavior of the hot electron transport through different target materials [17][18][19][20] or density gradients, 21 and their effect on proton acceleration at the target rear side. 22 Our study is motivated by a recent experiment of Gizzi et al, 23,24 who found that laser-driven ion beams have a much smaller (compared to that from an uncoated target) angular spread when the metal foil target is coated with a low Z (atomic number) dielectric layer. They attributed this effect to the self-generated magnetic field around the metaldielectric interface.…”

“…A more uniform electrostatic sheath field is thus formed at the back of the coated target, resulting in low emittance of the TNSA proton beams, in agreement with the experimental results. 23,24 II. SIMULATION MODEL AND RESULTS Figure 1 illustrates the target configuration and composition in our simulations.…”

“…The laser has a 100 fs duration with 16 fs rise/down time. Following Gizzi et al, 23 the target is a 5:7 lm flat aluminum foil coated on the right surface with a 1:5 lm thick CH layer. For TNSA, a 200 nm thick (protonrich) hydrogen layer is attached to the rear surface of the target.…”

Can proton radiography be used to image imploding target in ICF experiments?

“…In this paper we would like to summarize our previous work by introducing two criteria for PR resolution: the first called "strong condition" which require a very good proton beam quality in order to be satisfied; the latter, called "weak condition" is less stringent but give less information's on the target density profiles. These two The proton beam can be generated irradiating a thin metal layer (usually gold or titanium) using an ultra short (ps) and ultra high intensity (I ∼ 10 19 W/cm 2 ) laser beam according to the well-known TNSA process (Target Normal Sheet Acceleration) [3] the accelerated protons are characterized by small source, high degree of collimation, short durations and exponential decreasing energy spectrum [17]. In this section we introduce typical ICF experiment conditions showing briefly the setting of two important experiments which have been performed at the Vulcan Petawatt Laser in RAL one in 2006 to study the compression of a spherical target [8] and the latter in 2008 to study electron beam propagation in cylindrical compressed target [11].…”