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

摘要

A 248-nm excimer laser was used to produce ionized nitrogen by the process of multiphoton excitation in gaseous nitrogen at room temperature. First-negative N-2(+) emission spectra were analyzed to yield rotational temperatures of typically 600 to 1200 K. Rotational Raman scattering 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 temperature, but the room temperature value of 295 K was inferred from the H-2 Raman data. Therefore the use of N-2(+) spectra produced by multiphoton excitation at 248 nm does not appear to be acceptable for air-temperature diagnostics. N-2(+) emission spectra were also recorded subsequent to optical breakdown in air induced by Nd:YAG 1064-nm radiation, and temperatures were determined to be greater than 5000 K in the decaying plasma. [References: 8]