A device for recording an absorption spectrum of a fluid has a radiation source (1) that emits a radiation in a spectral range along a beam path (11), a measuring path (5), along which the radiation passes through the fluid and arranged in the beam path, a tunable Fabry-Perot interferometer (7), arranged in the beam path and transmitting radiation in the spectral range as a displaceable bandpass filter, and a detector (9, 35) measuring the intensity of the radiation in the spectral range. An etalon (3) is arranged for spectral modulation of radiation in the beam path and has a plurality of transmission maxima (17) in the spectral range. The bandpass filter, formed by the Fabry-Perot interferometer (7), is displacable across the spectral range such that spectral modulation of the radiation by the etalon (3) is measured by the detector (9, 35) as a modulation of radiation intensity over time.