Disclosed herein is a coherent dynamically controllable narrow band light source (10), comprising a first sub-light source (12), said first sub-light source being electrically controllable such as to generate controllable time-dependent intensity patterns of light having a first wavelength, a Raman active medium (30) suitable to cause Raman scattering of light having said first wavelength, a second sub-light source (20) capable of emitting light with a second wavelength, said second wavelength being longer than said first wavelength, and an optical fiber or wave guide, wherein said light emitted by said first and second sub-light sources traverses a length of said optical fiber (30) or wave guide in a feed-forward configuration to facilitate a non-linear wavelength conversion step involving said Raman-active medium. At least one of said first and second sub-light sources (12, 20) has a coherence length longer than 0.05 mm, preferably longer than 0.5 mm and most preferably longer than 2 mm.