A diffractive optical element device for use in spectroscopy, where broadband light is emitted from a light source (31) towards the optical element (24) and from there is transmitted to at least one detector (29; 29'). The optical element has a plurality of diffractive dispersively focusing patterns, preferably partly integrated into each other, whose respective centers are two-dimensionally offset relative to each other in order to produce a plurality of spectra (25 28), where at least two are separate, but offset relative to each other and/or partly overlapping. In an alternative embodiment, the optical element consists of either one diffractive optical element (60) that is related to a wavelength and produces a spectrum, or at least two diffractive optical elements (60, 61) which are related to respective wavelengths and which produce at least two mutually partly overlapping spectra to give a composite spectrum. Means are provided on or in connection with the optical element in order to produce in said spectrum at least one indication of upper and/or lower wavelength value.