An apparatus for inspecting a stream of matter , the apparatus comprising: - a first light source being adapted to emit a first light beam comprising wavelengths within a first wavelength range ( λ 1a - λ 1b ), for illuminating said stream of matter from side to side and, - a first detector arranged to receive said first light beam after it has been reflected against said stream of matter at a first detection area , - a second light source adapted to emit a second light beam comprising wavelengths within a second wavelength range (λ 2a -λ 2b ), for illuminating said stream of matter at an illuminated area , wherein any wavelength (λ 1 ) in said first wavelength range is different from any wavelength (λ 2 ) in said second wavelength range - a second detector being arranged to receive said second light beam after it has been reflected against said stream of matter at a second detection area , - a first scanning element being arranged between said stream of matter and said second detector and being adapted to redirect said second detection area from side to side across said stream of matter, further comprising - a beam splitting element arranged to receive said first light beam , after said first light beam has been reflected against said matter along a first optical axis , and arranged to receive said second light beam , after said second light beam has been reflected against said matter also along said first optical axis , wherein said beam splitting element is adapted to guide said reflected first light beam towards said first detector and to guide said reflected second light beam towards said second detector by redirecting one of said reflected first light beam and said reflected second light beam along a second optical axis non-parallel said first optical axis , the apparatus being characterised in that said scanning element is arranged between said beam splitting element and said second detector to receive only said reflected second light beam of said reflected first and second light beams. - a first light source being adapted to emit a first light beam comprising wavelengths within a first wavelength range ( λ 1a - λ 1b ), for illuminating said stream of matter from side to side and, - a first detector arranged to receive said first light beam after it has been reflected against said stream of matter at a first detection area , - a second light source adapted to emit a second light beam comprising wavelengths within a second wavelength range (λ 2a -λ 2b ), for illuminating said stream of matter at an illuminated area , wherein any wavelength (λ 1 ) in said first wavelength range is different from any wavelength (λ 2 ) in said second wavelength range - a second detector being arranged to receive said second light beam after it has been reflected against said stream of matter at a second detection area , - a first scanning element being arranged between said stream of matter and said second detector and being adapted to redirect said second detection area from side to side across said stream of matter, - a beam splitting element arranged to receive said first light beam , after said first light beam has been reflected against said matter along a first optical axis , and arranged to receive said second light beam , after said second light beam has been reflected against said matter also along said first optical axis , <EOS>