Editing Plasma diagnostics (section)

====Two-photon absorption laser-induced fluorescence====
TALIF is a modification of the laser-induced fluorescence technique. In this approach, the upper [[energy level]] is excited through the absorption of two photons, and subsequent fluorescence resulting from the radiative decay of the excited level is observed. TALIF is capable of providing precise measurements of absolute [[ground state]] atomic densities, such as those of hydrogen, oxygen, and nitrogen. However, achieving such precision necessitates appropriate calibration methods, which can be accomplished through titration or a more modern approach involving a comparison with a noble gases.<ref>{{cite journal |last1=Niemi |first1=Kari |title=Niemi, K., V. Schulz-Von Der Gathen, and H. F. Döbele. "Absolute calibration of atomic density measurements by laser-induced fluorescence spectroscopy with two-photon excitation |journal=Journal of Physics D: Applied Physics |date=2001 |doi=10.1088/0022-3727/34/15/312 |s2cid=250805163 |url=https://pure.qub.ac.uk/ws/files/551190/niemi01JPD34_2330.pdf }}</ref>

TALIF also offers insight into the temperature of species within the plasma, apart from atomic densities. However, this requires the use of lasers with a high [[spectral resolution]] to distinguish the Gaussian contribution of temperature broadening against the natural broadening of the two-photon excitation profile and the spectral broadening of the laser itself.