Schlieren imaging investigation of successive laser-induced breakdowns in quiescence atmospheric air

Wermer, Lydia; Im, Seong-kyun; Bak, Moon Soo

doi:10.2514/6.2016-0458

Cited by 3 publications

(2 citation statements)

References 12 publications

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“…These results show that for the selected dual-pulse set-up the shock loss increases of ≈ 3%, when compared with an equivalent single-pulse case (similarly to what is reported by An et al [48] for two 532 nm lasers having energies ⪆ 100 mJ each), but the amount of energy consumed by the shock wave is less than the one of a single LIB at the same total energy. This is consistent with experiments from Bak, Wermer et al [45,46], performed with combinations of successive 532 nm lasers with first and second pulse energies ranging from 5 mJ to 31 mJ and time intervals between pulses ranging from 50 ns to 100 µs. The set-up investigated in the current manuscript follows the dual-pulse strategy examined in the works of Butte et al [37] and Dumitrache et al [18], where a first UV low-energy laser (20 mJ) is used for pre-ionization and a second 40 mJ NIR discharge adds energy to the system for tailoring the plasma kernel (e.g.…”

Section: Post-discharge Dynamicssupporting

confidence: 91%

“…The LIB model predicts a more elongated and larger plasma kernel for the collinear dual-pulses. For LIB-seeded ignition, the control of electron temperature and size of the plasma kernel can promote flame stabilization and enhance flame speed, because the volume affected by the dual-pulse is larger than the one originated by a single laser pulse [45,46]. These simulations show how the collinear dual-pulse laser energy deposition might work advantageously, as suggested by recent experimental investigations [34,37].…”

Section: Comparison With Single Pulsesmentioning

confidence: 54%

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Collinear dual-pulse laser optical breakdown and energy deposition

Alberti¹,

Munafò²,

Pantano³

et al. 2020

J. Phys. D: Appl. Phys.

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A non-equilibrium model for laser-generated plasmas is used to represent collinear dual nano-second-pulse interactions. In the specific case considered, the breakdown is initiated with an ultraviolet (UV) laser pulse at 266 nm, which pre-ionizes the gas, and it is followed by a near-infrared (NIR) pulse at 1064 nm, which deposits significant energy into the ionized mixture. The model is validated against corresponding experiments, and simulation results are interrogated to understand key features of the plasma-kernel dynamics and the post-discharge hydrodynamics. The hydrodynamics of the non-equilibrium plasma is governed by the two-temperature Navier–Stokes equations accounting for both multiphoton ionization and inverse bremsstrahlung. The interaction between the laser beam and the plasma is modeled based on the radiative transfer equation. The temporal and spatial offsets of the two pulses can generate ionization kernels with different topology and dynamics. It is shown that the UV pre-ionization pulse can tailor the plasma region, leading to a larger ionized volume than would occur for a single-pulse breakdown, and it increases the efficiency of the energy deposition for the following NIR discharge. Vorticity in the early post-discharge phase is generated via baroclinic torque from the misalignment of the radial gradient of density (sudden gas expansion) and the strong pressure gradient (initiated by energy deposition from the laser beam). It is predicted that the collinear dual pulse can be designed to specify the plasma kernel size, shape, and maximum temperature in the breakdown phase, and the initial post-breakdown vorticity and plasma-core decay.

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