An apparatus for generating electromagnetic radiation pulses comprises a mode-locked laser oscillator with an oscillator cavity defining an oscillator beam path, a first gain element, first pumping means for pumping said first gain element, and a mode locker, and being operable to produce a train of seed electromagnetic radiation pulses. Further an optical switch is placed outside of the oscillator beam path and is arranged in a beam path of radiation coupled out from the oscillator, the optical switch operable to couple radiation from a switch input into a switch output during a certain time period or certain time periods. A radiation amplifier is arranged in a beam path of radiation radiated from the switch output. The amplifier includes a second gain element and second pumping means, the second pumping means comprising a continuous-wave pump radiation source.