Self-Absorption Corrections to Hydrogen and Aluminum Line Profiles in Laser-Induced Plasma

Laser-induced plasma is generated to study the Stark-broadened Balmer series hydrogen alpha line and the 3s23p � 3s24s aluminum 394.4 and 396.15 nm ground state transitions. Self-absorption effects are addressed by retro-reflecting plasma emissions through the plasma prior to spectroscopic imaging in order to determine wavelength dependent correction factors. The corrected line profiles are fit using Voigt profiles to de-convolve the instrument width from the Stark-broadened line component. At a time delay of 70 ns following plasma initiation, H� spectra show selfabsorption corrections; however, the electron density, Ne, that is determined from the H� line width remains the same. An electron number density of 2.4 ± 0.3 × 1018 cm-3 is found from the H� line width while the line shift shows a value of 2.2 ± 0.4 × 1018 cm-3. At similar time delays, the Al line at 394.4 nm shows a significant change under the influence of self-absorption as the spectral width reduces from 1.3 ± 0.2 to 0.9 ± 0.2 nm with a corrected Ne of 3.0 ± 1.0 × 10 18 cm-3. The Al 396.15 nm line is further distorted by the neighboring Al+ and N+ lines near 399.5 nm, making the selfabsorption tests inconclusive for this line. PACS Codes: 32.70.Jz, 33.70.Jg, 52.38.Mf, 52.50 Jm