Laser-driven proton acceleration from ultrathin foils is investigated experimentally using f /3 and f /1 focusing. Higher energies achieved with f /3 are shown via simulations to result from self-focusing of the laser light in expanding foils that become relativistically transparent, enhancing the intensity. The increase in proton energy is maximized for an optimum initial target thickness, and thus expansion profile, with no enhancement occurring for targets that remain opaque, or with f /1 focusing to close to the laser wavelength. The effect is shown to depend on the drive laser pulse duration.
We report on the generation of impurity-free proton beams from an overdense gas jet driven by a near-infrared laser (λ L = 1.053 µm). The gas profile was shaped prior to the interaction using a controlled prepulse. Without this optical shaping, a (30 ± 4) nC sr −1 thermal spectrum was detected transversely to the laser propagation direction with a high energy (8.27 ± 0.07) MeV, narrow energy spread ((6 ± 2) %) bunch containing (45 ± 7) pC sr −1 . In contrast, with optical shaping the radial component was not detected and instead forward going protons were detected with energy (1.32 ± 0.02) MeV, (12.9 ± 0.3) % energy spread, and charge (400 ± 30) pC sr −1 . Both the forward going and radial narrow energy spread features are indicative of collisionless shock acceleration of the protons.
Because of their ability to sustain extremely high-amplitude electromagnetic fields and transient density and field profiles, plasma optical components are being developed to amplify, compress, and condition high-power laser pulses. We recently demonstrated the potential to use a relativistic plasma aperture—produced during the interaction of a high-power laser pulse with an ultrathin foil target—to tailor the spatiotemporal properties of the intense fundamental and second-harmonic light generated [Duff et al., Sci. Rep. 10, 105 (2020)]. Herein, we explore numerically the interaction of an intense laser pulse with a preformed aperture target to generate second-harmonic laser light with higher-order spatial modes. The maximum generation efficiency is found for an aperture diameter close to the full width at half maximum of the laser focus and for a micrometer-scale target thickness. The spatial mode generated is shown to depend strongly on the polarization of the drive laser pulse, which enables changing between a linearly polarized TEM01 mode and a circularly polarized Laguerre–Gaussian LG01 mode. This demonstrates the use of a plasma aperture to generate intense higher-frequency light with selectable spatial mode structure.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.