an illumination subassembly configured to project illumination light towards the medium and an illumination light source operable to generate the illumination light and optically coupled to the illumination subassembly;

an imaging device configured to acquire an image of the medium including an analysis spot;

an excitation light source operable to generate an excitation light beam comprising an excitation wavelength selected to excite components present in the medium for the generation of photoluminescent light at an emission wavelength differing from the excitation wavelength;

a spectral analyser;

an optical assembly defining an imaging light path between the medium and the imaging device and a spectral analysis light path between the analysis spot on the medium and the spectral analyser,

the excitation light source being optically coupled to the spectral analysis light path for projecting the excitation light beam on said analysis spot, the spectral analyser being configured to analyse return light from the analysis spot as a function of wavelength; and

an optical filter coupled to the spectral analyser, the optical filter having a low light transmissivity at the excitation wavelength and a high light transmissivity at the emission wavelength.