Direct photoionization pumping of high gain VUV, UV and visible inversions in helium, cadmium and argon via two‐electron (shakeup) and of sodium via the output from the LLNL soft‐x‐ray laser

Picosecond two‐electron (shakeup) photoionization due to the soft‐x‐ray flux from a laser‐produced plasma has been used to produce 1.3 cm−1 gain in He+ on the H‐like 3−2 transition at 164.0 nm, 0.25 cm−1 gain in Cd+ on the 4d9 5s6s−4d9 5s5p transition at 205.5 nm and 0.9 cm−1 gain in Ar+ on the 3p4 4p−3p4 4s transitions at 427.7 and 476.5 nm. These results, when taken together with the earlier demonstrations of gain in Cd1 and Zn2 via one‐electron photoionization, suggest that it should be possible to produce gain in Na on the 2p5 3s−2p6 transition at 37.2 nm by photoionization sodium vapor with the 20.6 and 20.9 nm outputs from the Lawrence Livermore National Laboratory soft‐x‐ray laser.