Optimizing laser focal spot size using self-focusing in a cone-guided fast-ignition ICF target

Abstract

This paper presents a scheme for strong self-focusing of a laser beam interacting with a cone-guided fast-ignition inertial confinement fusion target using cone pre-plasma filling as an optical medium for reducing the laser beam waist. The objective is to reduce the focal spot size at the interior of the tip of the re-entrant cone to that required for efficient coupling to the dense imploded fuel core. This is challenging to achieve in a large laser system using the standard optical components of a chirped-pulse-amplified (CPA) laser-beam chain where the spot sizes produced are often significantly larger than would be desirable for fast ignition. The approach described also makes use of the presence of pre-plasma in the cone. Such pre-plasma filling is difficult to avoid entirely when illuminating a cone with a high-energy CPA laser system due to the challenges of reducing laser pre-pulse to below the threshold for plasma production. For deriving the differential equation which governs the progress of the laser beam-width with propagation distance, paraxial theory in a WKB approximation has been used. A simulation is performed assuming strong self-focusing in accordance with the laser parameters and plasma density profile chosen.

Towards bright gamma-ray flash generation from tailored target irradiated by multi-petawatt laser

“…In the present work, the default target referral is a tailored lithium target and the default laser power is 10 PW , except where it is stated otherwise. The conical-like cavity presently used resembles laser-target interaction geometries on which a cone is purposely fabricated at the target, aiming at novel fast-ignition schemes 64,65 , increasing laser induced γ-photon production 66 , enhancing laser field intensity 67 , and efficient proton acceleration 68,69 . The cavity formation in the radiation reaction regime is related to fast-ion ignition 70 and ion acceleration 71 .…”

Suppression of stimulated Raman scattering in magnetized plasma channel

“…SRS has gained considerable attention since the late 1960s owing to its significant potential in the field of Inertial Confinement Fusion. [1][2][3][4] SRS is a noteworthy issue that is not limited to the Inertial Confinement Fusion (ICF) procedure alone. Additionally, this phenomenon poses a noteworthy constraint in various high-power interactions between lasers and plasmas, such as electron acceleration, particularly laser wakefield and beat wave accelerators and THz radiation generation [5][6][7][8][9][10][11][12][13].…”

Stimulated Raman scattering by circularly polarized quadruple Gaussian laser beam and co-propagating electron beam in plasma

“…The intricate interplay between laser and plasma gives rise to a host of nonlinear phenomena, including self-focusing of propagating beams [7][8][9][10][11][12], filamentation [13], self-phase modulation [14], finite pulse effect [15], second harmonic generation [16], as well as the emergence of parametric instabilities [17] such as stimulated Brillouin scattering, stimulated Raman scattering (SRS) [18][19][20] and two-plasmon decay [21]. During the propagation of a laser beam through plasma, a portion of its energy is reflected due to the presence of various parametric instabilities, which assume critical significance in the context of ICF.…”