Emission characteristics and dynamics of species in a TEA-CO2 laser-produced CaO plasma

IBER2015, Aveiro, Portugal, 6th to 9th September of 2015; http://iber2015.web.ua.pt/Laser-produced plasmas (LPPs) are nowadays a topic of great interest in fundamental and applied areas of Physics such as the manufacture of thin films by pulsed laser deposition, spectrochemical analysis through laser-induced breakdown spectroscopy (LIBS) [1-3], production of nanoparticles, etc. Laser-target interaction involves complex processes and the analysis of LPPs can be very difficult considering its transient nature as well as large variations in plasma properties with space and time. In this work, we investigated the optical emission and imaging features of plasmas produced by a high-power laser [transversely excited atmospheric (TEA) CO2 and Nd: YAG] pulses on calcium oxide, CaO (Fig. 1). The analyzed plasma emission shows electronically excited neutral Ca and O atoms, ionized Ca+, Ca2+, O+, O2+ and O3+ species and molecular bands of CaOH (A2Π-X2Σ+, B2Σ+-X2Σ+ and D2Σ+- A2Π) (Fig. 2). We focus our attention on the dynamics of the CaO LPP species expanding into vacuum. In conventional one dimensional optical emission spectroscopy (OES) studies (Fig. 3), various plasma-plume segments were selected along the plume expansion axis and averaged over line-of-sight. The temporal evolution of spectral atomic and ionic line intensities at a constant distance from the target has been used to build optical timeof-flight profiles (TOF) (Fig. 4a). The velocity distributions that are derived from these TOF distributions are shown in Fig. 4b. Fig. 5 gives the time evolution of electron density and its first derivative with respect to time by setting the gate width of the intensifier at 0.1 μs. This setup was easily transformed to a two-dimensional (2D) OES setup by inserting a Dove prism between the focusing and collimating lenses (Fig. 1). Time and space-resolved 2D OES plasma profiles (Figs. 6 and 7) were recorded as a function of emitted wavelength and distance from the target. Fast side-on views of the plume expansion were made by recording overall visible emission from the plasma (Fig. 8). Emission intensities of axial area at 0.1 Pa as a function of the delay are given in Fig. 9a. The dynamic of the plume front was compared with the shock wave expansion model (Fig. 9b).Peer Reviewe