Imaging spectroscopy of polymer ablation plasmas for laser propulsion applications

Abstract

A number of polymers have been proposed for use as propellants in space launch and thruster applications based on laser ablation, although few prior studies have either evaluated their performance at background pressures representative of the upper atmosphere or investigated interactions with ambient gases other than air. Here, we use spatially and temporally resolved optical emission spectroscopy to compare three polymers, poly(ethylene), poly(oxymethylene), and glycidyl azide polymer, ablated using a 532 nm, nanosecond pulsed laser under Ar and O2 at pressures below 1 Torr. Emission lines from neutrally and positively charged atoms are observed in each case, along with the recombination radiation at the interaction front between the plasma plume and the background gas. C2 radicals arise either as a direct fragmentation product or by a three-body recombination of C atoms, depending on the structure of the polymer backbone, and exhibit a rotational temperature of ≈5000 K. The Sedov–Taylor point blast model is used to infer the energy release relative to the incident laser energy, which for all polymers is greater in the presence of O2, as to be expected based on their negative oxygen balance. Under Ar, plume confinement is seen to enhance the self-reactivity of the ejecta from poly(oxymethylene) and glycidyl azide polymer, with maximum exothermicity close to 0.5 Torr. However, little advantage of the latter, widely considered one of the most promising energetic polymers, is apparent under the present conditions over the former, a common engineering plastic.

Experimental Research on Impulse Coupling Characteristics and Plasma Plume Dynamics of a Nanosecond Pulsed Laser Irradiated Aluminum Target

“…Therefore, the shock wave model was suitable for the front propagation of the laserinduced plasma plume [21]. The Taylor-Sedov equation was employed to interpret the position change of the plasma plume [24], [39]:…”

“…E1 and a1 represent the energy release and the corresponding fitting constant at the fluence of 1 φ , respectively. Therefore, the energy coupling efficiency i η [39] at a certain laser fluence could be obtained as follows：…”

Glycidyl Azide Polymer and its Derivatives-Versatile Binders for Explosives and Pyrotechnics: Tutorial Review of Recent Progress

“…The concept of laser-induced polymer ablations was also approached by Jiao et al [101], who focused on the methodology of detecting laser-induced plasma plumes and identifying their components. By utilising optical emission spectroscopic imaging, the authors were able to elucidate the mechanisms underlying laser ablation from the three investigated polymers-polyethylene, poly(oxymethylene) and glycidyl azide polymer.…”

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

“…Pulsed laser ablation (PLA) has received extensive attention over the last two decades with applications in various fields like film deposition, nanoparticles fabrication, high precision laser processing, environmental analysis, surgery treatment, pulsed laser propulsion, etc. [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] .…”