Wavenumber linear spectrometers are provided including an input configured to receive electromagnetic radiation from an external source; collimating optics configured to collimate the received electromagnetic radiation; a dispersive assembly including first and second diffractive gratings, wherein the first diffraction grating is configured in a first dispersive stage to receive the collimated electromagnetic radiation and wherein the dispersive assembly includes at least two dispersive stages configured to disperse the collimated input; and an imaging lens assembly configured to image the electromagnetic radiation dispersed by the at least two dispersive stages onto a linear detection array such that the variation in frequency spacing along the linear detection array is no greater than about 10%.