Laser ablation of an indium target: time-resolved Fourier-transform infrared spectra of In I in the 700–7700 cm−1 range
Laser-induced breakdown spectroscopy (LIBS) in combination with a time-resolved Fourier-transform technique was applied to obtain spectra of In I in the infrared spectral region. This method was proven to be suitable for measuring the weak energy transitions between highly excited Rydberg atomic levels. The advantage comes from the possibility of selecting an optimal time-delay after the laser pulse, when the low intensity spectral lines are near their maximum intensity and can filter out the disturbing high intensity lines with different emission time profiles. The time-resolved spectra were recorded in the 700–1000, 900–1300, 1200–1680, 1800–4000, 4100–5000 and 5000–7700 cm−1 ranges with a resolution of 0.017 cm−1. Using this technique, we obtained five g- and h-levels of In I that have never been measured previously. We demonstrate a close similarity of wavenumbers for the 7s1/2–7p1/2 and 4f–5g transitions of the In atom.