Measurement of population inversion for FUV transitions in Kr-like YIV in a high-current reflex discharge

Kr-like ions are good candidates for FUV lasing since they can be produced in plasmas quite easily. We present results from a spectroscopic investigat ion of Y IV emission from a high current density, cold cathode reflex disch arge. The Y II to Y V emission is recorded in the 200-3000 Angstrom range u sing photometrically calibrated spectrometers, while the emission of trace aluminum ions serves for plasma diagnostics. The intensities of the Y TV 4d -5p and 5s7-5p transitions strongly increase relative to lines from Y II an d Y III with increasing plasma current. The spectra studied here are obtain ed at a current density of 1.75 A/cm(2). Experimental Y IV intensity ratios spanning several excited configurations are compared with collisional radi ative predictions of the HULLAC atomic physics package. Good agreement is f ound for the measured and predicted ratios of 4p(5)5p to 4p(5)5s level popu lations per statistical weight. Finally, the response of the Kr-like system to a fast, transient excitation pulse is examined using the RADEX code. La rge transient gains are predicted for several 5s-5p transitions in Kr-like Y IV.