Demonstration of soft x-ray laser of Ne-like Ar at 69.8 nm pumped by capillary discharge.

The demonstration of a 69.8 nm laser on 3p 3P2 - 3s 1P1 (J=2-1) transition of Ne-like Ar pumped by capillary discharge is reported in this Letter. A main current of 12 kA with rise time of 43 ns was chosen to generate the plasma in a 35 cm long capillary filling with pressure of Ar as low as 11 Pa, resulting in a gain coefficient of 0.34 cm(-1) and gain-length product of 11 at 69.8 nm. Also observed is a weak laser on 3p 3D2 - 3s 3P1 (J=2-1) transition of Ne-like Ar at 72.6 nm in the same condition. In addition, multiwavelength lasing at 46.9, 69.8, and 72.6 nm was simultaneously realized in a capillary discharge plasma column, conditioning the pressure of Ar to 13 Pa.