A fiber-laser-based implementation of a Gigahertz source through difference frequency generation (DFG) by nonlinear optical (NLO) materials is compact, tunable and scalable. A pair of pulsed fiber lasers, preferably single-frequency, generate output pulses at frequencies .omega.1 and .omega.2 that overlap temporally. A beam combiner combines the laser outputs and routes the combined output to a GHz generator head where a nonlinear interaction process in the NLO material generates GHz radiation.