New visible transitions in nitrogen ion lasers

The observation of five new N II laser lines, at 460.14, 460.71, 462.14, 464.30, and 648.18 nm, in a pure-nitrogen pulsed discharge is reported. A modified version of the axial-pulsed-discharge device described by Chiu and Chou (1981) is employed, with 4.6-mm-internal-diameter capillary tubing, 98-percent-reflectance, 400-670-nm-spectral-range, multilayer dielectric-coated TiO2 and SiO2 cavity mirrors, and either no series inductance (giving peak current 4400 A and current pulse width = 15 microsec) or 50 microhenry series inductance (1000 A and 7 microsec) in the circuit return path. A plane-grating spectrophotometer was used to record the laser and spontaneous emission lines, the positions being calibrated with Fe lines; 12 N lines with a total energy of about 10 mJ were observed. The strong line at 648.18 nm is characterized in detail: peak output is achieved at an operating pressure of about 3 mtorr, and laser pulse width is 30 microsec, beginning about 10 microsec after the current pulse.