Enhancing laser beam performance by interfering intense laser beamlets

Abstract

Increasing the laser energy absorption into energetic particle beams represents a longstanding quest in intense laser-plasma physics. During the interaction with matter, part of the laser energy is converted into relativistic electron beams, which are the origin of secondary sources of energetic ions, γ-rays and neutrons. Here we experimentally demonstrate that using multiple coherent laser beamlets spatially and temporally overlapped, thus producing an interference pattern in the laser focus, significantly improves the laser energy conversion efficiency into hot electrons, compared to one beam with the same energy and nominal intensity as the four beamlets combined. Two-dimensional particle-in-cell simulations support the experimental results, suggesting that beamlet interference pattern induces a periodical shaping of the critical density, ultimately playing a key-role in enhancing the laser-to-electron energy conversion efficiency. This method is rather insensitive to laser pulse contrast and duration, making this approach robust and suitable to many existing facilities.

Generation of α-Particle Beams With a Multi-kJ, Peta-Watt Class Laser System

“…In our experiment, the laser was typically delivering 1.4 kJ in 2.6 ps. The calculated focal spot size was ∼50 µm, which corresponds to an intensity on target of ∼ 2-3 × 10 19 W/cm 2 , taking into account the ∼50-60% encircled energy within the nominal focal spot [3]. A 25-µm-CH foil was used as pitcher target for the proton acceleration stage (TNSA regime).…”

“…In recent years, the interaction of high intensity laser beams with solid targets has paved the way to the generation of bright sources of protons (and different ion species) through the mechanisms of Target Normal Sheath Acceleration (TNSA) [1], including recent achievements with the LFEX PW-laser [2,3]. Laser driven acceleration of energetic He ions (α-particles) has remained mostly unexplored, with exception of experimental results related to investigation of alternative neutron-less fusion schemes, also known as proton-boron fusion (p-B) reaction [4][5][6][7][8]:…”

Laser produced electromagnetic pulses: generation, detection and mitigation

“…laser energy, intensity and focusing conditions. The conventional estimate of hot electron average energy, given in Equation 2, may be altered by effects such as stochastic heating [65] and direct laser acceleration under suitable conditions [66] . With increase of laser pulse energy and target size, more electrons are ejected.…”

Energetic α -particle sources produced through proton-boron reactions by high-energy high-intensity laser beams

“…The experiment was carried out at the Institute of Laser Engineering at Osaka University, Japan using the short-pulse, high-intensity, high-energy PW class laser LFEX [22]. During the campaign, laser energies varied between 1.2 and 1.4 kJ, in 2.7 ± 0.45 ps at the fundamental wavelength (λ = 1.05 μm).…”