Hot Electrons Transverse Refluxing in Ultraintense Laser-Solid Interactions

Abstract

We have analyzed the coupling of ultraintense lasers (at ∼2×10{19} W/cm{2}) with solid foils of limited transverse extent (∼10 s of μm) by monitoring the electrons and ions emitted from the target. We observe that reducing the target surface area allows electrons at the target surface to be reflected from the target edges during or shortly after the laser pulse. This transverse refluxing can maintain a hotter, denser and more homogeneous electron sheath around the target for a longer time. Consequently, when transverse refluxing takes places within the acceleration time of associated ions, we observe increased maximum proton energies (up to threefold), increased laser-to-ion conversion efficiency (up to a factor 30), and reduced divergence which bodes well for a number of applications.

Dose-controlled irradiation of cancer cells with laser-accelerated proton pulses

“…Yet, only with the recent generation of table-top 100 TW Ti:Sapphire lasers, operating at pulse repetition rates of up to 10 Hz, energies exceeding 10 MeV [14][15][16][17][18] became accessible for applications where also the average dose rate is of interest, e.g., for providing sufficiently short treatment durations of a few minutes. For the anticipated future application in radiation therapy, a further increase in the proton energy of up to 200-250 MeV is required, which is currently addressed by the investigation of novel acceleration schemes [19][20][21] as well as by ongoing laser development.…”

Manipulation of the spatial distribution of laser-accelerated proton beams by varying the laser intensity distribution

“…27. The initial transverse sheath expansion velocity is set equal to 0.7c (as determined from a previous experiment 8 and simulations 28 ), and it decreases exponentially with a 1/e time constant of 60 fs. The rate of reduction in the transverse expansion velocity is based on time-and spaceresolved interferometry measurements of a probe beam reported in Ref.…”

“…The rate of reduction in the transverse expansion velocity is based on time-and spaceresolved interferometry measurements of a probe beam reported in Ref. 8, scaled to the shorter laser pulse used in the present work. The sheath evolution is calculated in 0.8 fs steps.…”

“…The pulse duration, at the source, is short, and the transverse emittance is very low. [6][7][8] Potential applications in medicine, material science, accelerator physics, and industry, for example, have been widely discussed. 3,9 However, in order to become a useful source for applications, a number of parameters must be greatly improved.…”

Efficient ion beam generation in laser interactions with micro-structured targets

“…Maximum proton energy and energy transformation have been enhanced in the recent experiments by reducing the foil thickness [3] and lateral dimensions of the target [4]. However, high laser contrast is inevitable for such experiments in order to avoid premature target disruption.…”