Different methods can be used to concentrate the power generated by a storage-ring free-electron laser into a series of giant pulses. One of these techniques, Q-switching, is based on a periodically induced detuning between the electron bunches circulating into the ring and the light pulse stored in the optical cavity. Such a method has been recently implemented at ELETTRA. This new regime significantly improves the peak power and the reproducibility of laser signal making the source more reliable. A full characterization of such an operation mode is presented in this paper. (C) 2004 Published by Elsevier B.V.