In a laser beam source for projecting laser pulses, having a laser-active medium (10), a controllable pump device (11) for exciting the medium (10), a resonator (13) for inducing oscillation of the medium (10), which resonator has an end mirror (14) and an output mirror (15) with an orientation axially parallel to the medium (10), for the sake of projecting laser pulses of constant pulse energy immediately upon release of the laser beam source, one of the resonator mirrors (14) is pivotably supported and is pivoted out of its resonator position and back into its resonator position by an actuator (19) at selectable times (FIG. 1).