We report optical amplification of ${\mathrm{Ar}}_2^{*}$ at $126\mathrm{nm}$ , pumped by optical-field-induced ionization (OFI) created by an infrared high-intensity laser. A gain–length product of 0.84 was obtained by using multipass amplification with a vacuum ultraviolet (VUV) cavity. The gain–length product was increased up to 4.3 through the use of single-pass amplification with a VUV reflector and a hollow $5.0\mathrm{cm}$ -long fiber. Similar small signal gain coefficients of 0.84 and $0.86{\mathrm{cm}}^{-1}$ were obtained in two different experiments, in which OFI Ar plasma gain media were produced in free space filled with Ar and inside an Ar-filled hollow fiber.