Visible emission from C2 and CN during cw laser-irradiated graphite

Abstract. Porous graphite samples were irradiated with up to 3.5  kW/cm2 and 1 MJ deposited energy from a continuous wave ytterbium 1.07-μm fiber laser. Visible emission spectroscopy reveals C2 Swan (d3Πg−a3Πu) Δv=±2,±1, and 0 sequences, CN red (A2Π−X2Σ+) Δv=−4,−3 sequences, CN violet (B2Σ+−X2Σ+) Δv=+1,0 sequences, and Li, Na, and K2P3/2,1/2−S1/22 doublets. Surface temperatures increased from ∼2500  K at 0.7  kW/cm2 to ∼4000  K at 3.5  kW/cm2. Spectral emissivity at 3.9  μm ranging from 0.74 to 0.93 increases by ∼8% after laser irradiation. Spectral simulations demonstrate that the ratio of C2(d) and CN(A) column densities are independent of sample porosity. Column densities increase from 0.00093 to 1.6×1012  molecules/cm2 for CN(A) and 0.00014 to 1.4×109  molecules/cm2 for C2(d) as laser intensity increases from 1.4 to 3.5  kW/cm2. Surface temperatures increase by 134 K and CN(A) and C2(d) emissions increase by 100% and 4200%, respectively, in stagnation air flow of 5  m/s.

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