We observed a small-signal gain of Ar<sub>2</sub><sup>*</sup> emission at 126 nm by use of a hollow fiber to guide the high-intensity laser propagation in high-pressure Ar. The small-signal gain coefficient was measured to be 0.05 cm<sup>-1</sup> at 126nm. Kinetic analysis revealed that the electrons produced by the high-intensity laser through an optical-field-induced ionization process initiated the Ar<sub>2</sub><sup>*</sup> production processes. The increase in the emission intensity was measured to be exp(2.5), with an increase in the fiber length.
© 2003 Optical Society of America
Masanori Kaku, Takeshi Higashiguchi, Shoichi Kubodera, and Wataru Sasaki, "Observation of vacuum-ultraviolet Ar2* radiation gain at 126 nm produced by an ultrashort high-intensity laser pulse propagating in a hollow fiber," Opt. Lett. 28, 804-806 (2003)