The wavelength resolved spectra recorded during subnanosecond depletion of the gain in a KrF laser amplifier have been used to specify the state responsible for the dip in the KrF(B --> X) emission spectra. Self-absorption of the KrF laser emission at 248.9 nm has been found to be due to the phototransition from the KrF(C) state to a (2)Pi Rydberg state. (C) 2000 American Institute of Physics. [S0021-9606(00)01506-3].