Apparatus 10 for detecting Raman spectral features of a sample 12 under ambient light 14, comprises； a CCD 40 having a plurality of pixels comprising detection pixels 42 and storage pixels 44； a laser 26 arranged to illuminate the sample and collection optics 36 to direct scattered light from the sample to the detection pixels； a controller 60 arranged to implement an exposure period during which are interleaved first and second intervals； the first interval being for accumulation of first (background or Raman) spectral signals at the detection pixels； the second interval being for accumulation of second Raman spectral signals at the detection pixels； wherein during the first interval the first spectral signals are further accumulated in the detection pixels while storing the accumulated second Raman spectral signals in the storage pixels； and during each second interval the second Raman spectral signals are accumulated in the detection pixels while storing the accumulated first spectral signals in the storage pixels.
