Abstract: A tunable source of narrowband coherent radiation comprises a pulsed pump laser (10), an optical parametric oscillator or amplifier (12) and a so-called master oscillator (14). The narrowband output radiation of the master oscillator serves as seed radiation which is injected into the optical parametric oscillator or amplifier (12). In order to obtain a beam profile of the emitted output radiation as homogeneous as possible, optically imaging elements (28) are arranged in an optical delay line (24) for the partial pulses which pump the optical parametric oscillator or amplifier, which transform the spatial beam profile at the output (30) of the pump laser (10) with respect to amplitude, phase and, preferably, the divergence, too, into the crystal of the optical parametric oscillator or amplifier.