Active manipulation of the spatial energy distribution of laser-accelerated proton beams

Abstract

The spatial energy distributions of beams of protons accelerated by ultrahigh intensity (>10(19)Wcm2) picosecond laser pulse interactions with thin foil targets are investigated. Using separate, low intensity (<10(13)Wcm2) nanosecond laser pulses, focused onto the front surface of the target foil prior to the arrival of the high intensity pulse, it is demonstrated that the proton beam profile can be actively manipulated. In particular, results obtained with an annular intensity distribution at the focus of the low intensity beam are presented, showing smooth proton beams with a sharp circular boundary at all energies, which represents a significant improvement in the beam quality compared to irradiation with the picosecond beam alone.

Effects of front surface plasma expansion on proton acceleration in ultraintense laser irradiation of foil targets

“…In agreement with previous observations reported in Carroll et al (2007), we measure significant improvements in the uniformity and circularity of the beam over the full proton energy range. In agreement with previous observations reported in Carroll et al (2007), we measure significant improvements in the uniformity and circularity of the beam over the full proton energy range.…”

Ballistic Focusing of Polyenergetic Protons Driven by Petawatt Laser Pulses

“…Indeed, as can be seen by comparing the divergence characteristics for two different ion front shapes shown in the Ref. [17] with the divergence characteristic shown in Fig. 4(b), the 250 m thick target resembles closely the case of an inverse parabolic or truncated Gaussian plasma front.…”

“…By suppressing the hot electron refluxing the wings of the Gaussian ion front can be suppressed (as demonstrated in the Ref. [17]), and will allow the whole beam to emerge ballistically. Refluxing can be significantly constrained by increasing target thickness.…”

“…Thus the dynamics of the beam divergence depends on the shape of the plasma front at the beginning of free propagation, which in turn depends upon the hot electron distribution across the target rear surface producing the accelerating sheath [16]. Since the emergence of a proton beamlet is defined by the local normal to the sheath, an expanding plasma front (isodensity contour at a given time) of Gaussian shape [15][16][17] will give a curved trajectory to the beam emerging from the wings (the area beyond the inflection point) of the sheath, as shown schematically in the Fig. 4(a).…”

Time and space resolved interferometry for laser-generated fast electron measurements

“…To illustrate the capability of the diagnostic, we show here results obtained when irradiating aluminum targets with thickness 9.4-25 m using a laser with intensity of ϳ5 ϫ 10 19 W / cm 2 . 37 Data points have been taken at radial distances of approximately every 6 m, according to the spatial resolution of the diagnostic. Focusing of the main interaction laser was achieved using a f / 3 off-axis parabola.…”