Mitigation of laser plasma parametric instabilities with broadband lasers

Abstract

Laser plasma instabilities (LPIs) cause laser energy loss, asymmetric and insufficient compression, and target preheating, thus are assumed to be among the major concerns of inertial confinement fusion research. Mitigation of LPIs can enhance the laser–target coupling efficiency and optimize the target compression dynamics, which is critical for the realization of robust and high-efficiency fusion ignition. Broadband lasers with polychromatic components or random phases have been investigated for decades as an effective alternative to mitigate LPIs. Here, we present a brief overview on the progress of broadband LPIs, including the models of broadband lasers, the involved physics, the conditions for effective suppression of LPIs, and some schemes to produce broadband lasers.

Control of laser-plasma instabilities by non-collinear polychromatic light

“…, where ⃗ k Lj and ∆κ j = a j k Lj √ ω pe (ω j − ω pe )/(ω 2 j − 2ω j ω pe ) are the wavevector of Langmuir wave and the width of instability region driven by the jth beam [47]. The widest instability region is found at the backscattering mode.…”

“…In our previous work [63], we assumed that δK ′ 0x ∼ δk ′ 0x at n e < 0.1n c0 . The exact expression for the saturation gain in underdense plasmas is [47,65]…”

“…At present, no practical scheme has been demonstrated for the efficient third-harmonic generation (THG) of broadband lasers [39][40][41][42] because the phase-matching conditions required for THG are difficult to satisfy [43][44][45]. Collinear polychromatic light (CPL) with multicolor beamlet propagation in the same direction was thus proposed [46,47], which can effectively mitigate LPIs without technical obstacles. However, the optical system is complicated and overloaded for practical applications because each CPL requires at least four color collinear beamlets.…”

“…In contrast to conventional broadband lasers [47], in this article, we propose the LPI model and optical design for non-collinear polychromatic light (NCPL) that has a nonzero angle between different-color beamlets with detuning ≳1%. Theoretical models of NCPL show that beamlets are noncollinear if the introduced angle satisfies α ≳ 3 • , and therefore the wavevector couplings of LPIs are reduced.…”

Effect of THz-bandwidth incoherent laser radiation on bulk damage in potassium dihydrogen phosphate crystals

“…These interactions limit the amount of energy that can be deposited on target and significantly limit the efficiency of the process. Simulation results suggest that these interactions can be significantly suppressed by utilizing an incoherent broadband driving field 5 – 7 . Recent efforts to realize such a source based on novel optical parametric amplifier (OPA) technology, which amplify fluorescence-based seed light, producing nanosecond pulses with an incoherent bandwidth of 10 THz have been demonstrated 8 – 10 .…”