Disclosed herein is a system (10) for measuring light induced transmission or reflection changes, in particular due to stimulated Raman emission. The system comprises a first light source (12) for generating a first light signal having a first wavelength, a second light source (14) for generating a second light signal having a second wavelength, an optical assembly (16) for superposing said first and second light signals at a sample location (18), and a detection means (24) for detecting a transmitted or reflected light signal, in particular a stimulated Raman signal caused by a Raman-active medium when located at said sample location. Here in at least one of the first and second light sources (12, 14) is one or both of actively controllable to emit a time controlled light pattern or operated substantially in CW mode and provided with an extra cavity modulation means (64) for generating a time controlled light pattern. The detection means (24) is capable of recording said transmitted or reflected light signal, in particular stimulated Raman signal, as a function of time.