A capacitively coupled longitudinally pumped excimer laser (248 nm) was actively mode-locked with an acousto-optic modulator based on a quartz substrate and driven at 100 MHz. The construction of such a laser is simple because the KrF mixture is excited in a small capillary glass tube along the laser axis. A train of five pulses with a maximum single pulse of 0.2 muJ and a duration of 1.3 ns was obtained.