A vital signs monitoring system which comprises at least one optical vital signs sensor (100) configured to measure or determine vital signs of a user and to output an output signal. Said optical vital signs sensor (100) comprises at least one laser light source (110) configured to generate laser light, which is directed towards a skin (1000) of a user, and at least one photo detector unit (120) configured to detect light which is indicative of an absorption or reflection of the laser light from the at least one light source (100) in or from the skin (1000) of the user. The vital signs monitoring system comprises a coherence distortion unit (200) which is in a first operational mode configured to distort a wavefront of the laser light from the at least one laser light source (110) such that non-coherent light is directed towards the skin (1000) of a user and which is in a second operational mode configured to deactivate the distortion of the wave front of the laser light such that coherent light is directed towards the skin (1000) of a user.
