Abstract
We experimentally investigated the accelerated proton beam characteristics such as maximum energy and number by varying the incident laser parameters. For this purpose, we varied the laser energy, focal spot size, polarization, and pulse duration. The proton spectra were recorded using a single-shot Thomson parabola spectrometer equipped with a microchannel plate and a high-resolution charge-coupled device with a wide detection range from a few tens of keV to several MeV. The outcome of the experimental findings is discussed in detail and compared to other theoretical works.
Highlights
The acceleration of protons and ions during the interaction of high-power laser pulses with solid targets has been a well-investigated field since the first experimental study in the 1980s [1]
We investigated the dependence of proton emission on laser intensity by varying the pulse energy on the target from 10 mJ up to 650 mJ in steps < 100 mJ while keeping the pulse duration and focus spot size fixed
By following a similar approach as in the case of P-polarization, we found that κ = 0.08 and the reduced electron temperature Te = 40 keV, which corresponds to a sheath field of ETNSA = 3 × 1010 volume (m−3) TNSA electric field (V/m), to be compared to ∼ 7 × 1011 V/m at the focus position
Summary
The acceleration of protons and ions during the interaction of high-power laser pulses with solid targets has been a well-investigated field since the first experimental study in the 1980s [1]. For relatively long λ g (sub-wavelength or larger), an electron plasma wave can be resonantly excited along the direction of the density gradient, and part of the laser energy is transferred to the electrons This is called resonance absorption, [22] and the electron temperature scales as Thot ∝ (Iλ2 )1/3. Vacuum heating or Brunel absorption [20] becomes important; in this case, a strong energy absorption can be accounted for by the electrons that are dragged into the vacuum and sent back into the plasma with velocities equivalent to the quiver velocity vosc = eE/me ω This mechanism is more efficient than resonant absorption for vosc /ω > λ g and the electron temperature scales as Thot ∝ (Iλ2 )α , where α > 1. We present and discuss our experimental findings on the influence of different laser polarization (P, S, and 45◦ ) on the number and energy of protons when varying laser intensity, pulse duration, and laser spot size are on the target
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