Abstract: A radiation pulse generating assembly comprises a radiation generator such as a laser for generating pulses of radiation having pulse widths in the order of pico seconds. The pulses from the generator are coupled onto an optical fiber which causes the pulses to undergo Raman scattering to generate reduced width pulses with wavelengths lying within a Raman spectrum and having widths in the order of femto seconds. A first filter filters out the initial pump wavelength while a second filter downstream of the first filter is tunable to select reduced width pulses within a desired wavelength band.