A spectrometer (100; 200; 300) for analysing the spectrum of an upstream light beam including: - an entrance slit adapted to let said upstream light beam through, - collimation means adapted to generate, from said upstream light beam, a collimated light beam, and - angular dispersion means arranged so as to intercept said collimated light beam and to angularly disperse said collimated light beam according to a plurality of wavelengths (λ1, λ2), said spectrometer being characterized in that: - said angular dispersion means comprise at least one polarization-separation diffraction grating that has a normal N to the grating, said polarization-separation diffraction grating being adapted to diffract said collimated light beam into: - at least one first diffracted light beam (11, 12) according to a first diffraction order that is either the diffraction order +1, or the diffraction order -1 of said polarization-separation diffraction grating, said first diffracted light beam (11, 12) being angularly diffracted according to said plurality of wavelengths (λ1, λ2) and having a first polarization state that is circular, and - a second diffracted light beam (21, 22) according to a second diffraction order that is either the diffraction order +1, or the diffraction order -1 of said polarization-separation diffraction grating, said second diffraction order being different from said first diffraction order, said second diffracted light beam (21, 22) being angularly diffracted according to said plurality of wavelengths (λ1, λ2) and having a second polarization state that is circular and orthogonal to said first polarization state, and in that it includes: - optical recombination means (130; 330; 430) arranged at least on an optical path of said second diffracted light beam (21, 22), downstream of said polarization-separation diffraction grating, said optical recombination means (130; 330; 430) comprising at least one planar optical-reflection surface (130; 331; 432) parallel to said normal N to the grating that is adapted to deviate at least said second diffracted light beam (21, 22), and - focussing means adapted to focus, for each wavelength of said plurality of wavelength (λ1, λ2), said first diffracted light beam (11, 12) and said second diffracted light beam (21, 22) to a same focussing surface. - an entrance slit adapted to let said upstream light beam through, - collimation means adapted to generate, from said upstream light beam, a collimated light beam, and - angular dispersion means arranged so as to intercept said collimated light beam and to angularly disperse said collimated light beam according to a plurality of wavelengths (λ1, λ2), - said angular dispersion means comprise at least one polarization-separation diffraction grating that has a normal N to the grating, said polarization-separation diffraction grating being adapted to diffract said collimated light beam into: - at least one first diffracted light beam (11, 12) according to a first diffraction order that is either the diffraction order +1, or the diffraction order -1 of said polarization-separation diffraction grating, said first diffracted light beam (11, 12) being angularly diffracted according to said plurality of wavelengths (λ1, λ2) and having a first polarization state that is circular, and - a second diffracted light beam (21, 22) according to a second diffraction order that is either the diffraction order +1, or the diffraction order -1 of said polarization-separation diffraction grating, said second diffraction order being different from said first diffraction order, said second diffracted light beam (21, 22) being angularly diffracted according to said plurality of wavelengths (λ1, λ2) and having a second polarization state that is circular and orthogonal to said first polarization state, and - at least one first diffracted light beam (11, 12) according to a first diffraction order that is either the diffraction order +1, or the diffraction order -1 of said polarization-separation diffraction grating, said first diffracted light beam (11, 12) being angularly diffracted according to said plurality of wavelengths (λ1, λ2) and having a first polarization state that is circular, and - a second diffracted light beam (21, 22) according to a second diffraction order that is either the diffraction order +1, or the diffraction order -1 of said polarization-separation diffraction grating, said second diffraction order being different from said first diffraction order, said second diffracted light beam (21, 22) being angularly diffracted according to said plurality of wavelengths (λ1, λ2) and having a second polarization state that is circular and orthogonal to said first polarization state, and - optical recombination means (130; 330; 430) arranged at least on an optical path of said second diffracted light beam (21, 22), downstream of said polarization-separation diffraction grating, said optical recombination means (130; 330; 430) comprising at least one planar optical-reflection surface (130; 331; 432) parallel to said normal N to the grating that is adapted to deviate at least said second diffracted light beam (21, 22), and - focussing means adapted to focus, for each wavelength of said plurality of wavelength (λ1, λ2), said first diffracted light beam (11, 12) and said second diffracted light beam (21, 22) to a same focussing surface.