A method and a sensor for detecting a target gas by laser spectroscopy using a laser or a laser diode having a monochrome emission wavelength that can be modulated by varying the operating temperature or the operating current. The wavelength range of the target gas comprises a first modulation of the laser or the laser diode over a first large modulation width, in addition to at least two absorption lines of a reference gas and at least one absorption line of the target gas. The absorption lines are used to calibrate the wavelength scale of the laser or the laser diode in relation to the varied operating temperature or operating current, a second modulation of the laser or the laser diode being performed over a second small modulation width, with the at least one absorption line of the target gas, for detecting the target gas.