A high resolution spectrometer with a large free spectral range comprising an entry slit for a beam of electromagnetic radiation to be analyzed, a first dispersion device for dispersing the beam to be analyzed into various wavelength components in a first direction, a second dispersion device for dispersing each wavelength component output from the first dispersion device in a second direction, and an imaging device comprising a sensitive detection spectrum. surface on which the beam dispersed in the first and second directions is focused, the first dispersion device being an optical filter that varies linearly and has a surface on which the beam to be analyzed is focused, each point on the surface of the filter operating like a pass band filter with a central frequency varying linearly in the first direction.