5.5–7.5 MeV Proton Generation by a Moderate-Intensity Ultrashort-Pulse Laser Interaction withH2ONanowire Targets

Abstract

We report on the first generation of 5.5-7.5 MeV protons by a moderate-intensity short-pulse laser (∼5×10(17) W/cm(2), 40 fsec) interacting with frozen H(2)O nanometer-size structure droplets (snow nanowires) deposited on a sapphire substrate. In this setup, the laser intensity is locally enhanced by the snow nanowire, leading to high spatial gradients. Accordingly, the nanoplasma is subject to enhanced ponderomotive potential, and confined charge separation is obtained. Electrostatic fields of extremely high intensities are produced over the short scale length, and protons are accelerated to MeV-level energies.

Proton Acceleration by Ultrashort Intense Laser Interaction with Microstructured Snow Targets

“…The Coulomb explosion of the positively charged whisker, add longtime acceleration to the protons. A one dimensional fluid model, demonstrating the field enhancement by an order of magnitude by the local plasma density near the whisker tip, was presented in our previous work [15].…”

“…Using structured snow targets and relatively low contrast ratio this scaling was demonstrated for significantly lower laser powers than the traditional schemes [14,18]. Moreover, in experiments that were carried out at laser system with high contrast ratio (short pulse prepulse with energy below microjoule), where the main pulse interacted directly with solid snow surface, the protons were accelerated to much lower energy [14][15][16]. The high proton energy can be attributed to combination of several effects: The improved laser absorption [18] and the interaction of the laser with mass limited plasma with density gradient induced by the prepulse lead to significant enhancement of its effective electrical field [16].…”

“…Recently, we have demonstrated an alternative approach to laser-based proton acceleration by using a moderate power laser system and micro-structured snow targets [14][15][16]. These targets were engineered by depositing snow on sapphire substrates.…”

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

“…Laser absorption may be boosted by the presence of a nanostructure on the target surface, as was demonstrated experimentally [5] for thick targets. A boost in proton acceleration was observed in thin targets with nanostructure on the front (laser) side via numerical simulations [6] and experimentally [7] for lower intensities. We have proposed to increase the absorption efficiency by using a monolayer of nanospheres on the targets front side [8].…”

Ion motion effects on the generation of short-cycle relativistic laser pulses during radiation pressure acceleration

“…These events jeopardize the relativistic interaction of the ultra-thin target. Thus, high-contrast [9][10][11][12][13][14][15][16][17][18][19][20] and short-duration laser pulses [21,22] are needed. Plasma mirrors may be a feasible method by which to solve these problems.…”