Apparatus for and method of generating multiple laser beams using multiple laser chambers. The relative timing of the beams is controllable so they may, for example, be interleaved, may overlap, or be prevented from overlapping, or may occur in rapid sequence. The beams may have different spectral and power characteristics such as different wavelengths. Also disclosed is a system in which at least one of the multiple laser chambers is configured to generate radiation of two different wavelengths.