Laser ablation induced vapor plume expansion into a background gas. II. Experimental analysis

Abstract

Laser ablation of copper with a 4ns laser pulse at 1064nm was studied with a series of synchronized shadowgraph (100fs laser pulses at 400nm) and emission images (spectral line at 515nm). Data were obtained at two laser pulse energies (10 and 30mJ) and in three background gases (He, Ne, and Ar) at atmospheric pressure. The laser energy conversion ratio and the amount of sample vaporized for ablation in each condition were obtained by the theoretical analysis reported in paper I from trajectories of the external shock wave, internal shock wave, and contact surface between the Cu vapor and the background gas. All three quantities were measured from shadowgraph and emission images. The results showed that E, the amount of energy that is absorbed by the copper vapor, decreases as the atomic mass of the background gas increases; and M, the mass of the sample converted into vapor, is almost independent of the background gas [Horn et al., Appl. Surf. Sci. 182, 91 (2001)]. A physical interpretation is given based on the phenomena observed in shadowgraph and emission images during the first tens of nanoseconds after the beginning of the laser pulse for ablation in different background gases. In addition, an internal shock wave was observed in the emission images during the first tens of nanoseconds after the laser pulse, which strikes the surface and should be one of the mechanisms inducing the liquid sample ejection. Also, a significant vortex ring near the target was observed in emission images at longer times after the laser pulse (>100ns) which distorts the otherwise hemispherical expansion of the vapor plume.

Study by focused shadowgraphy of the effect of laser irradiance on laser-induced plasma formation and ablation rate in various gases

“…This complexity is also apparent when one surveys the various studies on the influence of gas composition on the ablation rate (mass removed per laser shot), since whereas many recent numerical simulations and experiments have demonstrated that gas composition has little influence on the ablation rate, [19][20][21] many others have reported its influence over the analytical signal. For example, recent simulations from the Russo group based on the previous work of Predtechensky and Mayorov [22] and of Arnold et al [21] suggest that the process of energy coupling from the laser pulse to the sample surface is a very short phenomenon that occurs only in the very early phase of the plasma propagation.…”

Influence of Carrier Gas Flow Rate, Laser Repetition Rate, and Fluence on the Size Distribution and Number of Nanoparticles Generated Per Laser Shot During Paint Laser Ablation

“…The final number per shot of particles is only determined by the puff residence time in the setup (evolution of durations t 1 and t 2 ). This hypothesis can be considered because of the significant difference between the orders of magnitude of the gas speed in the cell (a few meters per second) and of the ablation plume speed (typically several hundreds of meters per second; Kokai et al 1999;Hauer 2004;Liu 2005;Wen et al 2007aWen et al , 2007b. This suggests that the puff occupies its volume V 0 quasi instantly whatever the air flow rate in the cell is.…”

Pulse energy packing effects on material transport during laser processing of $$<1|1|1>$$ < 1 | 1 | 1 > silicon

“…In the nanosecond regime, thermal and structural effects dominate with melt expulsion being the dominant material removal mechanism, at moderate fluence levels [20]. Recoil pressure resulting from the emission of a shockwave as well as backward travelling shockwaves have been attributed to material ejection when it interacts with an interface separating two different fluids, known as the the Richtmyer-Meshkov instability [33]. Molten material is often observed long after pulse termination, demonstrated in the case of nanosecond pulses [30,31] and involves the interplay of several phenomena including hydrodynamic instabilities and vapour-assisted ejection.…”