An open-path tunable laser spectrometer for measuring a concentration of a selected trace gas, the open-path laser spectrometer comprising: an open-path multi-pass analysis arrangement comprising a first mirror, a second mirror at a distance from the first mirror, and a support structure for locating the first and second mirrors (108, 109); a laser coupled to the open-path multi-pass analysis arrangement and configured to emit light of a tunable wavelength range and to enable a plurality of reflections of the emitted light between the first and second mirrors (108, 109); a detector coupled to the open-path multi-pass analysis arrangement and configured to detect a portion of the emitted light upon interaction with the selected trace gas and impinging on the detector and to generate a signal corresponding to a characteristic of the detected portion of the emitted light; an electronic system coupled to the laser and the detector, comprising a processor configured to measure the concentration of the selected trace gas based on the generated signal by calculating one or more spectral characteristics of the generated signal and comparing the one or more spectral characteristics against predetermined reference data; characterised in that: the laser comprises a thermoelectric cooler, TEC, configured to control a temperature of an emission source of the laser, and the processor is configured to adjust the wavelength range of the emitted light by the laser by: controlling an injected DC current to the laser to tune the laser wavelength; assessing, based on the generated signal, linecentres of the selected trace gas resonances in relation to laser current; detecting a wavelength shift in the spectrum of the light emitted by the laser; and signalling the TEC to control the temperature of the emission source of the laser to compensate for the wavelength shift in the spectrum, based on the generated signal. an open-path multi-pass analysis arrangement comprising a first mirror, a second mirror at a distance from the first mirror, and a support structure for locating the first and second mirrors (108, 109); a laser coupled to the open-path multi-pass analysis arrangement and configured to emit light of a tunable wavelength range and to enable a plurality of reflections of the emitted light between the first and second mirrors (108, 109); a detector coupled to the open-path multi-pass analysis arrangement and configured to detect a portion of the emitted light upon interaction with the selected trace gas and impinging on the detector and to generate a signal corresponding to a characteristic of the detected portion of the emitted light; an electronic system coupled to the laser and the detector, comprising a processor configured to measure the concentration of the selected trace gas based on the generated signal by calculating one or more spectral characteristics of the generated signal and comparing the one or more spectral characteristics against predetermined reference data; characterised in that: the laser comprises a thermoelectric cooler, TEC, configured to control a temperature of an emission source of the laser, and the processor is configured to adjust the wavelength range of the emitted light by the laser by: controlling an injected DC current to the laser to tune the laser wavelength; assessing, based on the generated signal, linecentres of the selected trace gas resonances in relation to laser current; detecting a wavelength shift in the spectrum of the light emitted by the laser; and signalling the TEC to control the temperature of the emission source of the laser to compensate for the wavelength shift in the spectrum, based on the generated signal. the laser comprises a thermoelectric cooler, TEC, configured to control a temperature of an emission source of the laser, and the processor is configured to adjust the wavelength range of the emitted light by the laser by: controlling an injected DC current to the laser to tune the laser wavelength; assessing, based on the generated signal, linecentres of the selected trace gas resonances in relation to laser current; detecting a wavelength shift in the spectrum of the light emitted by the laser; and signalling the TEC to control the temperature of the emission source of the laser to compensate for the wavelength shift in the spectrum, based on the generated signal.