An apparatus for carrying out Raman spectroscopy on a sample the apparatus comprising: a light source for providing a beam of excitation radiation, and an optical system providing an optical light path for directing the beam of excitation radiation to the sample and for directing a beam of scattered light from the sample to a detector, the optical system comprising a spectrograph, the spectrograph comprising a grating, in particular a transmission grating, adapted to divide the beam of scattered light into a spectrum of spatially separated wavelength components and to direct at least a portion of the spectrum to the detector, the spectrograph comprising a first lens system in the light path between the grating and the detector for focussing the portion of the spectrum onto the detector, the optical system comprising at least a second lens system (103, 147), in particular in the light path between the light source and the sample, and the second lens system (103, 147) being configured to provide a first focal plane with at least a first focal point (105, 105a, 105b) in the optical path for focussing the beam of excitation radiation and/or the beam of scattered radiation at the first focal point (105, 105a, 105b), and the apparatus comprising a reference sample arranged in the focal plane, in particular at the first focal point (105, 105a, 105b), for obtaining a reference spectrum from the reference sample, wherein the optical system comprises a polarization selective element for splitting the beam of excitation radiation into two beams (15a, 15b) of excitation radiation with orthogonal polarization, wherein one of the two beams is focused to a first focal point in the focal plane where the reference sample is placed and the other one of the two beams is focused to another first focal point which is not blocked by the reference sample. a light source for providing a beam of excitation radiation, and an optical system providing an optical light path for directing the beam of excitation radiation to the sample and for directing a beam of scattered light from the sample to a detector, the optical system comprising a spectrograph, the spectrograph comprising a grating, in particular a transmission grating, adapted to divide the beam of scattered light into a spectrum of spatially separated wavelength components and to direct at least a portion of the spectrum to the detector, the spectrograph comprising a first lens system in the light path between the grating and the detector for focussing the portion of the spectrum onto the detector, the optical system comprising at least a second lens system (103, 147), in particular in the light path between the light source and the sample, and the second lens system (103, 147) being configured to provide a first focal plane with at least a first focal point (105, 105a, 105b) in the optical path for focussing the beam of excitation radiation and/or the beam of scattered radiation at the first focal point (105, 105a, 105b), and the apparatus comprising a reference sample arranged in the focal plane, in particular at the first focal point (105, 105a, 105b), for obtaining a reference spectrum from the reference sample, wherein the optical system comprises a polarization selective element for splitting the beam of excitation radiation into two beams (15a, 15b) of excitation radiation with orthogonal polarization, wherein one of the two beams is focused to a first focal point in the focal plane where the reference sample is placed and the other one of the two beams is focused to another first focal point which is not blocked by the reference sample.