An optical pulse source for generating optical supercontinuum pulses comprises an optical pump laser operable to generate optical pump pulses at a pump pulse repetition rate Rf; a nonlinear optical element comprising an optical fiber for generating optical supercontinuum pulses; an optical modulator operable to selectively control the launch of pump pulses into the optical fiber at a reduced, lower repetition rate Rr=Rf/N in order to generate optical supercontinuum pulses at a selectable and lower repetition rate; an optical fiber amplifier located between the optical modulator and the optical pump laser; wherein the optical supercontinuum pulses generated by the optical fiber have a supercontinuum spanning from below 450 nm to greater than 2000 nm; wherein the optical pulse source is provided with a microprocessor configured to determine when supercontinuum pulses are delivered; and wherein the optical pulse source is configured to provide an output trigger signal.