Planar laser-induced fluorescence imaging of Cu atom and Cu2 in a condensing laser-ablated copper plasma plume

Abstract

Planar laser-induced fluorescence (PLIF) is used to monitor Cu atoms and Cu2 produced by excimer laser ablation of a copper target (308 nm, ≳10 J/cm2, 1–3 GW/cm2) expanding rapidly into helium background gas at pressures ranging from 10 to 100 Torr. The Cu2 results from gas phase condensation of the copper atoms ablated from the target in the regions of highest Cu atom density as expected, but the maximum Cu2 laser-induced fluorescence (LIF) signal occurs significantly after the maximum of the Cu signal. Rotationally resolved excitation scans of Cu2 utilizing the A–X (0,0) transition indicate that the Cu2 has reached equilibrium with the 300 K background gas. An extensive search for Cu3 via LIF failed, indicating that Cu3 is present only in very low ‘‘steady state’’ number density in the plume. This data is explained qualitatively by a simple kinetic model. In addition to the kinetic information, it is clear from the PLIF images that viscous eddy formation becomes more pronounced as the backing gas pressure increases; however, we see no evidence of turbulence in the plume even at the highest backing gas pressure studied. The PLIF technique allows us to observe the onset of condensation directly as well as to obtain information about the expansion dynamics of the plume not easily obtainable by other means.

Polar distribution of ablated atomic material during the pulsed laser deposition of Cu in vacuum: Dependence on focused laser spot size and power density

“…34 With a background gas, LIF was used to detect Cu and Cu 2 , with condensation of Cu to form Cu 2 shown to require the presence of the background gas. 35,36 Macroscopic molten globules emitted from the irradiated target, deposited upon the substrate as particulates, represented less than 1% of the total area of the substrate for our experimental data. In addition, such globules are not emitted from the irradiated target in any preferred direction, forming a cos 4 distribution upon the substrate.…”

“…35͒ and 10-30ϫ10 8 W/cm 2 . 36 Within vacuum, laser induced fluorescence ͑LIF͒ was used to detect Cu and Cu 2 with the LIF signal for Cu shown to be approximately 10 3 that for Cu 2 . 34 With a background gas, LIF was used to detect Cu and Cu 2 , with condensation of Cu to form Cu 2 shown to require the presence of the background gas.…”

The Langmuir probe as a diagnostic of the electron component within low temperature laser ablated plasma plumes

“…Complex diagnostic systems, typically based on either tunable dye laser sources or broad band light sources coupled to monochromators, are used to probe the plasma plume using interferometry, absorption spectroscopy, and laser induced fluorescence techniques. [3][4][5][6][7][8][9][10][11] However such systems are liable to be too expensive and complex for industrial uptake, and here we examine the merits of a simpler diagnostic based on a Langmuir probe. 12 Langmuir probe diagnostic systems are typically applied to quiescent, homogenous plasma, which can be maintained for considerable durations measured in minutes if not hours.…”

Ablation plume structure and dynamics in ambient gas observed by laser-induced fluorescence imaging spectroscopy

“…Around the same time, the LIF imaging technique using a sheet-shaped laser beam was introduced to observe the cross-sectional structure of the irradiated portion of a plume [32][33][34][35]. Nakata et al compared the expansion characteristics of ground state and highly excited atoms using fluorescence and emission imaging spectroscopy [36].…”