Characterization of laser induced plasmas in nitrogen using an ungated spectrometer

The effects of pressure and laser energy on the excitation temperature, electron number density and spark energy of laser induced plasmas (LIPs) in nitrogen were investigated using an ungated spectrometer with an electron multiplying charge-coupled device (EMCCD) camera as the detector. The plasmas were generated in nitrogen of 1.2×104 Pa to 1.0×105 Pa by 532 nm output of a 10 Hz Q-switched Nd:YAG laser with pulse energy ranging from 20 mJ to 100 mJ. The excitation temperatures were found around 3 eV, and varied little with pressure and laser energy. The electron number densities increased from 5.8×1017 cm−3 to 4.7×1018 cm−3 when the pressure was increased from 1.2×104 Pa to 1.0×105 Pa, but varied little with laser energy. The spark energy increased linearly with the input laser energy, and saturated at 35-60% of the input energy. Comparisons with results of time-resolved measurements and of other authors indicate that the ungated spectrometer can give reasonable results on excitation temperature and electron number density of LIPs, although it suffers intrinsic limitations involved with its inability to be time-resolved, and can serve as an option to lower systematic cost for practical applications of laser induced plasmas.

► Laser induced plasmas in nitrogen are characterized using an ungated spectrometer. ► Electron temperatures are ∼3.0 eV, and vary little with laser energy and pressure. ► Electron densities increase with pressure, but vary little with laser energy. ► Time-resolved measurement confirmed the reliability of the ungated measurements.