Transport of YO molecules produced by ArF laser ablation of YBa2Cu3O7−δ in ambient oxygen gas

Abstract

One-dimensional-imaging laser-induced fluorescence spectroscopy (1D-LIF) has been applied to investigate the dynamics of the nonemissive neutral particles (YO molecules) during the ArF excimer laser ablation of YBa2Cu3O7−δ in an ambient oxygen gas. Investigating the 1D-LIF observation, the propagation of particles through the ambient gas at appropriately high pressures is categorized into two phases, the propagation phase and the diffusion phase. In the propagation phase, the point source blast wave model (shock model) describes well the dynamics at high background gas pressures. Particles propagate according to the shock model over a finite distance from the pellet surface after the ablation, and almost stop there. The propagation distance depends on the ambient gas pressure and the ablation fluence. After the propagation ceases, the particles start to diffuse through the background gas; that is the diffusion phase. Rotational temperature variations of YO molecules in the different phases are also measured. Rotational temperatures as high as 1000 K are observed even in the diffusion phase.

Expansion dynamics of the plasma produced by laser ablation of BaTiO3 in a gas environment

“…For pressures above this threshold, t M increases sharply, this increase being consistent with the reduction in the ejected species velocity that has been widely reported in the literature in the presence of a gas environment. 4,5,[7][8][9]12 Figure 3͑b͒ includes the t M values not only for the emission line at 553.6 nm ͑Ba*͒, but also for that at 493.4 nm ͑Ba ϩ *). It is clearly seen that the results are very similar for both species, with the same results observed both for the maximum emission intensity curve, which is not shown in Fig.…”

“…At higher pressures, the formation of a blast wave has been observed. 4,5,25 Under these conditions the shock wave model describes well the plasma expansion for a limited range of distances that depend on the gas pressure 4,5,7 and is determined by ͑a͒ the distance from the target at which the mass of the gas displaced by the ejected material is much higher than the mass of the ejected material and ͑b͒ the distance from the target at which the plasma pressure becomes similar to the pressure of the gas environment. The expression for the shock wave is…”

“…5͒ is a clear indication that the plasma expansion dynamics in the presence of a gas change with respect to the free-expansion dynamics followed in vacuum or for low pressures/short distances. 4,5,7,8,24 Under these conditions, the plasma expansion process in a gas environment has been analyzed in terms of different models depending on the pressure range. For the early stages of expansion and at low pressures ͑Ͻ1 mbar͒, a drag model has been considered, 7 which accounts for the scattering of the ejected species by the gas atoms or molecules.…”

“…If one takes into account that the shock wave model can strictly be applied only after the mass of the gas surrounding the shock wave is higher than the mass of the ablated material 5,7 ͑i.e., a time t s after the laser pulse͒, a delayed shock wave should be considered as has been suggested elsewhere. 25 In this case, the expression for the shock wave becomes…”

“…3 The plasma expansion dynamics produced by laser ablation of HTSC targets has been widely studied. [4][5][6][7][8][9] These studies have shown that parameters such as the laser energy density or the gas pressure determine the nature, 6,10,11 kinetic energy, [7][8][9]12 and distribution of species reaching the substrate, 12,13 thus, influencing the morphology, homogeneity, and crystalline characteristics of the deposited films. [13][14][15] Similar results have already been reported for BaTiO 3 films, since the ferroelectric response, the refractive index, the composition, and the crystalline orientation of the films have been found to depend on the laser energy density and oxygen pressure.…”