Abstract: A directly modulatable laser comprising an active medium inside a laser cavity formed by a resonator mirror and an out-coupling mirror, and a pump light source exciting the active medium. It is characterized in that the active medium generates radiation of two wavelengths (&lgr;1 and &lgr;2) and the resonator mirror is constructed as a controllable reflector by which the reflectivity is controllable for each of the two wavelengths (&lgr;1 and &lgr;2) and the controllable reflector is connected with a control unit, wherein the reflection factor is controlled in such a way that the inversion density of the electrons which is generated in the active medium is constant and the light output of one of the wavelengths ((&lgr;1) is controllable between a minimum value and a maximum value according to an applied control signal, wherein the control of the two wavelengths ((&lgr;1 and &lgr;2) is carried out in push-pull.