Demonstration of transient gain x-ray lasers near 20 nm for nickellike yttrium, zirconium, niobium, and molybdenum

We demonstrate strong lasing on the Ni-like 4d S-1(0) --> 4p P-1(1) transition at 18.9, 20.3, 22.0, and 24.0 nm for Mo, Nb, Zr, and Y ions, respectively, using the transient collisional excitation scheme. Approximately 5 J of laser energy in a combination of a 600-ps pulse and a l-ps pulse from the Compact Multipulse Terawatt (COMET) tabletop laser system is used to irradiate slab targets of these materials. Small-signal gains of 17-26 cm(-1) are determined on the 4d --> 4p transition, with overall gain-length products gL of 11-12. Lasing is observed and gain is measured on the 4f P-1(1) --> 4d P-1(1) transition, which is pumped by collisional excitation combined with self-photopumping, for what is to our knowledge the first time. (C) 1999 Optical Society of America.