A spectrometer is provided which comprises a Virtually Imaged Phased Array member configured to receive an electromagnetic input radiation and to generate an electromagnetic output radiation, in which a spectrum of the electromagnetic output radiation is dispersed along a dispersion axis (x) transverse to an optical axis (z) of propagation of the electromagnetic output radiation; a Fourier lens adapted to convert the output electromagnetic radiation into a spectral pattern; an image sensor adapted to detect the spectral pattern; and at least one diffraction mask arranged along the optical axis (z) for propagating the output electromagnetic radiation, in a position not coincident with a spectral plane of the spectrometer. Through the diffraction mask, which comprises a material blocking the transmission of the output electromagnetic radiation, an aperture is obtained which allows the transmission of the output electromagnetic radiation, and whose edge comprises at least one inclined segment.