The XeF* and F* sidelight emissions, the small‐signal gain, and the transient plasma absorption near the laser wavelength have been measured from a XeF self‐sustained discharge laser. We conclude that the production of XeF* in its lower vibrational levels requires collisions with He atoms, and that XeF* decays predominantly by radiative processes and He quenching. The transient absorption at the laser wavelength, believed to be due to F−, F*, F*2, and Xe+2, can be as large as ∼1–2%/cm at small‐signal gains of ∼8%/cm.