Fine structure and spectral broadening of Balmer lines in laser-produced plasmas

The profiles of the Balmer lines emitted in a laser-produced plasma by the ions ${\mathrm{B}}^{4+}$ to ${\mathrm{F}}^{8+}$ have been observed. For the Balmer-$\ensuremath{\alpha}$ line the fine-structure components are broadened and partially merged by the Stark effect, the thermal Doppler broadening, and the motional Doppler shift. To these lines a simplified model for an expanding plasma, used previously for the analysis of the Lyman lines of the same ions, has been applied. The results are in very good agreement with the observations, showing the overall validity of the interpretation. The various broadening mechanisms have been unfolded and in particular for the range of electron densities considered here a transition between the weak- and strong-field approximations for the Sark broadening is evident.