Wavelength-dependent variations of the electron characteristics in laser-induced plasmas: A combined hydrodynamic and adiabatic expansion modelling and time-gated, optical emission imaging study

Abstract

The spatial and temporal evolution of the absolute electron densities and temperatures in plasmas formed by nanosecond pulsed laser ablation of silicon in vacuum at two wavelengths (1064 and 532 nm), at similar irradiances, have been explored by complementary simulation (using combined hydrodynamic and adiabatic models) and experiment. Modelling the laser-target and laser-plume interactions with the POLLUX code reveals the evolving composition and dynamics of the laser induced plasma (LIP) during the incident laser pulse: 532 nm irradiation causes more ablation, but the LIP formed by 1064 nm excitation has a higher average charge state and expands faster. The experimental data, from the analysis of Stark broadened line shapes of SiIII and SiIV cations in time-gated, position- and wavelength-resolved images of the plume emission, allow characterisation of the plume dynamics at later times. These dynamics are compared with predictions from two forms of adiabatic expansion model. Both take as input parameters the plume properties returned by the POLLUX simulations for the end of the laser pulse, but differ according to whether the initial plasma is assumed isothermal or isentropic. The study illustrates the important λ-dependences of the target absorption coefficient (in establishing the ablated material density) and of electron–ion inverse bremsstrahlung absorption (in coupling laser radiation into the emergent plasma); the extents to which these interactions, the relative ablation yields, and the plume expansion dynamics depend on λ; and the importance of identifying appropriate initial conditions for adiabatic expansion modelling of LIP in vacuum.

Enhanced X-ray emission arising from laser-plasma confinement by a strong transverse magnetic field

“…( 3 ) can be easily modified to the following: where is the initial value of a bare nuclei concentration at time . Here we consider the plasma to expand adiabatically 76 , 77 with a fixed velocity , where x is the distance from the target surface where the electron density drops as 1/e. It gives the opportunity to modify Eq.…”

Optical emission spectrometric diagnosis of laser-induced plasma and shock front produced at moderate pressure

“…As shown in Fig. 4, the expansion of the Si IV species (e.g., the 2p 6 Such multi-dimensional data sets like Fig. 4 allow detailed analysis of plume dynamics.…”

“…[1][2][3][4][5] . Despite the popularity of PLA, the mechanisms of laser ablation are obscured by coupled interactions of laser-plasma, laser-target, and plasma-ambient gas, ranging from super heated target surface emission to fast evolving plasma produced at vaccum or moderate pressure [6] . The hydrodynamic model [7] was found as an appropriate method to simulate the plasma at surrounding pressures of 10 2 -10 5 Pa.…”

Modelling of Plasma Temperatures and Densities in Laser Ablation Plumes of Different Metals

“…Pert et al [20][21][22][23] to model pulsed nanosecond laser ablation and the evolution of a plasma plume as it expands and travels over time. In addition to the work by Qaisar et al, mentioned before [13], POLLUX has been used for the study of laser ablation of copper [5] and silicon targets [24]. Laser interaction with the material target and laser interaction with the subsequent plasma plume are both included in POLLUX.…”