Spatially resolved spectra of resonantly pumped laser produced plasmas of lithium

Spatially resolved visible spectra emitted from a plasma formed by focusing the output of a flashlamp pumped dye laser onto solid targets of lithium have been recorded. The effects of laser wavelength on plasma formation have been analyzed by tuning the laser to the first resonance transition in lithium at 6708 A and comparing the results with those obtained at an off resonance wavelength of 6728 A. Laser energies varied from 430 to 645 mJ and were focused to a spot diameter of 300 μm with a pulse length of 850 ns. Light from the plasma was focused onto the slit of a Hilger spectrograph, which incorporated a Pellin–Broca prism whose output was focused onto a charge-coupled device camera. Electron densities of 1016–1018 cm−3 were deduced from Stark width and shift measurements of the Li II 2s–2p line at 5485 A and from the Li I 2p–4d line at 4603 A. In this way the electron density could be mapped as a function of distance from the target. By observing emission at 5485 A the electron density was observed t...