Optical emission spectroscopic study of plasma plumes generated by IR CO2 pulsed laser on carbon targets

Optical emission spectroscopy studies, in the spectral range ultraviolet-visible-near infrared (UV-Vis-NIR), were performed to investigate thermal and dynamical properties of a plume produced by laser ablation of a graphite target. Ablation is carried out using a high-power IR CO2 pulsed laser at lambda = 9.621 mu m, power density ranging from 0.22 to 5.36 GW cm(-2) and air pressures around 4 Pa. The strong emission observed in the plasma region is mainly due to electronic relaxation of excited C, ionic fragments C+, C2+ and C3+ and molecular features of C-2(d (3) Pi(g)-a (3) Pi(u); Swan band system). The medium-weak emission is mainly due to excited atomic N, H, O, ionic fragment C4+ and molecular features of C-2(E (1) Sigma(+)(g)-A (1) Pi(u); Freymark system), C-2(D (1) Sigma(+)(u)-X (1) Sigma(+)(g); Mulliken system), CN(D (2) Pi-A (2) Pi), C-2(e (3) Pi(g)-a (3) Pi(u); Fox-Herzberg system), C-2(C (1) Pi(g)-A (1) Pi(u); Deslandres-d'Azambuja system), OH(A (2) Sigma(+)-X (2) Pi), CH(C (2) Sigma(+)-X (2) Pi), NH(A (3) Pi-X (3) Sigma(-)), CN(B (2) Sigma(+)-X (2) Sigma(+); violet system), CH(B (2) Sigma(+)-X (2) Pi), CH(A (2) Delta-X (2) Pi), C-2(A (1) Pi(u)-X (1) Sigma(+)(g); Phillips system) and CN(A (2) Pi-X (2) Sigma(+); red system). An excitation temperature T-exc = 23 000 +/- 1900 K and electron densities in the range (0.6-5.6) x 10(16) cm(-3) were estimated by means of C+ ionic lines. The characteristics of the spectral emission intensities from different species have been investigated as functions of the ambient pressure and laser irradiance. Estimates of vibrational temperatures of C-2 and CN electronically excited species under various laser irradiance conditions are made.