Rare-Gas pumping efficiencies for neodymium lasers

A comparison of rare-gas flashlamps for pumping YAG: Nd³⁺and neodymium-doped glass, which shows krypton lamps to be superior to xenon under certain circumstances, is presented. The emission spectra of argon have the best match to the neodymium absorption spectra, but argon lamps suffer from low radiative efficiency except at very high pressures. A detailed analysis of theoretical laser thresholds, which takes into account pump-pulse duration, cavity transfer coefficient, laser rod diameter, lamp emission spectra, and other pertinent parameters, is compared to experimental threshold data with good agreement. Krypton at 500-mm pressure gives a 19-percent improvement in the YAG : Nd³⁺threshold over a comparable xenon lamp at low current densities. Xenon is generally superior to krypton for pumping glass rods because of the greater absorption at 5900 Å where xenon is intrinsically a better radiator. However, proper lamp optimization shows a definite improvement in threshold with krypton at low drive levels. Xenon is anticipated to be superior to krypton at high current densities since line radiation will no longer contribute significantly to the pumping process. Proper optimization of lamp and cavity parameters should permit a slope efficiency of ∼6 percent for neodymium lasers to be realized.