TEMPERATURE-MEASUREMENTS FROM FIRST-NEGATIVE N-2 SPECTRA PRODUCED BY LASER-INDUCED MULTIPHOTON IONIZATION AND OPTICAL-BREAKDOWN OF NITROGEN

A 248-nm excimer laser was used to produce ionized nitrogen by the pro cess of multiphoton excitation in gaseous nitrogen at room temperature . First-negative N-2(+) emission spectra were analyzed to yield rotati onal temperatures of typically 600 to 1200 K. Rotational Raman scatter ing of H-2 in gaseous mixtures of N-2 and H-2 was used to determine if laser heating of the gas produced the observed increase in temperatur e, but the room temperature value of 295 K was inferred from the H-2 R aman data. Therefore the use of N-2(+) spectra produced by multiphoton excitation at 248 nm does not appear to be acceptable for air-tempera ture diagnostics. N-2(+) emission spectra were also recorded subsequen t to optical breakdown in air induced by Nd:YAG 1064-nm radiation, and temperatures were determined to be greater than 5000 K in the decayin g plasma.