Absorption spectrometer for measuring the concentration of a gaseous component of interest in a measurement gas, comprising - a variable-wavelength laser, - a detector for generating a measurement signal, - a multi-reflection gas cell situated in the light path between the laser and the detector and containing the measurement gas, - control means (6, 7, 9, 11, 13, 26) for varying the injection current (i) of the laser, to tune the wavelength of the light to a specific absorption line of the gaseous component of interest, and - analysis means for analysing the measurement signal and establishing a measured result for the concentration to be measured, characterised in that - the control means contain one or two pilot signal generators (11, 16) to modulate the injection current (i) alternately or simultaneously with two pilot frequencies (f P1, f P2) in the MHz range and - further analysis means are present to analyse signal components contained in the measurement signal with the pilot frequencies (f P1, f P2) in a phase-sensitive manner in each case, to establish a difference (Δφ meas) between the items of phase information (φ 1, φ 2) of the two signal components obtained in this operation and on the basis of said difference (Δφ meas) - to determine the length (L meas) of the light path, with the aid of which the measured result is established immediately from the absorption represented by the measurement signal or is corrected by comparing with a length (L calib) obtained during calibration of the absorption spectrometer or the known length (L 0) of the light path as a function of the relationship between the two compared lengths (L meas, L calib or L 0), or - to correct the measured result by comparing with a difference (Δφ calib) of the phase information obtained during calibration of the absorption spectrometer as a function of the relationship between the two compared differences (Δφ meas, Δφ calib). - a variable-wavelength laser, - a detector for generating a measurement signal, - a multi-reflection gas cell situated in the light path between the laser and the detector and containing the measurement gas, - control means (6, 7, 9, 11, 13, 26) for varying the injection current (i) of the laser, to tune the wavelength of the light to a specific absorption line of the gaseous component of interest, and - analysis means for analysing the measurement signal and establishing a measured result for the concentration to be measured, - the control means contain one or two pilot signal generators (11, 16) to modulate the injection current (i) alternately or simultaneously with two pilot frequencies (f P1, f P2) in the MHz range and - further analysis means are present to analyse signal components contained in the measurement signal with the pilot frequencies (f P1, f P2) in a phase-sensitive manner in each case, to establish a difference (Δφ meas) between the items of phase information (φ 1, φ 2) of the two signal components obtained in this operation and on the basis of said difference (Δφ meas) - to determine the length (L meas) of the light path, with the aid of which the measured result is established immediately from the absorption represented by the measurement signal or is corrected by comparing with a length (L calib) obtained during calibration of the absorption spectrometer or the known length (L 0) of the light path as a function of the relationship between the two compared lengths (L meas, L calib or L 0), or - to correct the measured result by comparing with a difference (Δφ calib) of the phase information obtained during calibration of the absorption spectrometer as a function of the relationship between the two compared differences (Δφ meas, Δφ calib). - to determine the length (L meas) of the light path, with the aid of which the measured result is established immediately from the absorption represented by the measurement signal or is corrected by comparing with a length (L calib) obtained during calibration of the absorption spectrometer or the known length (L 0) of the light path as a function of the relationship between the two compared lengths (L meas, L calib or L 0), or - to correct the measured result by comparing with a difference (Δφ calib) of the phase information obtained during calibration of the absorption spectrometer as a function of the relationship between the two compared differences (Δφ meas, Δφ calib).