Efficient, ultra-narrow spectral output from an electron-beam excited XeF(

) laser medium has been achieved by injection-controlled tuning. Using a pulsed dye laser as the injection source, amplified output pulses tunable between 435 and 535 nm and having a spectral width of 0.001 nm were obtained. For a 482.5 nm injection wavelength that is well matched to the XeF(

) gain maximum, output energy density and intrinsic efficiency values of approximately 8 J/l and 6 percent were achieved.