Ultraviolet versus infrared: Effects of ablation laser wavelength on the expansion of laser-induced plasma into one-atmosphere argon gas

Abstract

Laser-induced plasma from an aluminum target in one-atmosphere argon background has been investigated with ablation using nanosecond ultraviolet (UV: 355 nm) or infrared (IR: 1064 nm) laser pulses. Time- and space-resolved emission spectroscopy was used as a diagnostics tool to have access to the plasma parameters during its propagation into the background, such as optical emission intensity, electron density, and temperature. The specific feature of nanosecond laser ablation is that the pulse duration is significantly longer than the initiation time of the plasma. Laser-supported absorption wave due to post-ablation absorption of the laser radiation by the vapor plume and the shocked background gas plays a dominant role in the propagation and subsequently the behavior of the plasma. We demonstrate that the difference in absorption rate between UV and IR radiations leads to different propagation behaviors of the plasma produced with these radiations. The consequence is that higher electron density and temperature are observed for UV ablation. While for IR ablation, the plasma is found with lower electron density and temperature in a larger and more homogenous axial profile. The difference is also that for UV ablation, the background gas is principally evacuated by the expansion of the vapor plume as predicted by the standard piston model. While for IR ablation, the background gas is effectively mixed to the ejected vapor at least hundreds of nanoseconds after the initiation of the plasma. Our observations suggest a description by laser-supported combustion wave for the propagation of the plasma produced by UV laser, while that by laser-supported detonation wave for the propagation of the plasma produced by IR laser. Finally, practical consequences of specific expansion behavior for UV or IR ablation are discussed in terms of analytical performance promised by corresponding plasmas for application with laser-induced breakdown spectroscopy.

Characteristics of the ablation plume induced on glasses for analysis purposes with laser-induced breakdown spectroscopy

“…The used experimental setup is described in detail elsewhere [18][19][20][21][22], we provide here its brief description. Two Q-switched Nd:YAG lasers were used for ablation with IR (1064 nm) or UV (266 nm) radiation, with a repetition rate of 10 Hz and a pulse duration of 5 ns.…”

“…Quite different properties can be expected for ablation plumes induced on the surface of these two types of materials, which obviously leads to specific considerations when optimizing experimental conditions for LIBS analyses. Up to now, even though extensive studies have been devoted to the characterization of plasma induced on metallic samples [13][14][15][16][17][18][19][20][21][22], the investigation of the plasma induced on the surface of dielectric materials remains rare. Main interests were focused on the influence of the ablation wavelength on the analytical performance of the induced plasma [23,24].…”

Convoluted effect of laser fluence and pulse duration on the property of a nanosecond laser-induced plasma into an argon ambient gas at the atmospheric pressure

“…Our previous works show that such fluence is already high enough, especially for an IR pulse, to induce a strong post-ablation interaction leading to a strong plasma shielding. 4 The behaviors of the plasmas induced by the short pulse and the long pulse will first be compared in detail over the delay interval between 500 ns and 2 ls. The observations clearly show different behaviors between the plasmas produced by these two types of pulse.…”

Accuracy improvement of quantitative analysis by spatial confinement in laser-induced breakdown spectroscopy

“…The sensitivity of LIBS can be significantly improved using the methods described above [19,20]. However, there are two drawbacks: one is the increased complexity of the LIBS setup, and the other is the increased cost of using more than one laser.…”