A method for operating an optical measuring system with a wavelength-tunable temperature-stabilized laser light source for measuring the concentration of a target gas ZG in a measured gas, provided that an instantaneous base current I DC_ZG,act corresponding to a wavelength λ ZG of a target gas absorption line is set so that, after a calibration, the wavelength distance Δλ DC between the wavelength λ ZG of the target gas absorption line for the target gas ZG and a wavelength λ RG of a reference gas absorption line for a reference gas RG is maintained for the instantaneous base current I DC_ZG,act of the target gas ZG and for the instantaneous base current I DC_RG,act of the reference gas RG, characterized in that the calibration of the measuring system is performed with the reference gas RG and the target gas ZG, whereby during calibration - the base currents I DC_RG,cal and I DC_ZG,cal assigned to the gas absorption lines for the reference gas RG and for the target gas ZG are established, - the associated electrical powers P DC_RG,cal and P DC_ZG,cal of the laser light source are determined from the base currents I DC_RG,cal and I DC_ZG,cal as well as from the associated internal resistances R I_RG,cal and R I_ZG,cal, - a power difference ΔP DC,cal is found by means of the electrical powers P DC-RG,cal and P DC_ZG,cal and this or one or more equivalent variables are stored in the measuring system, and that during operation of the measuring system a temperature difference in the laser light source, defined in advance during the calibration, between the operating points selected at the time of calibration of the reference gas RG, with a base current I DC_RG,cal ascertained during the calibration and the target gas ZG, with a base current I DC_ZG,cal ascertained during the calibration, is maintained by way of determining an necessary instantaneous base current I DC_ZG,act for the target gas ZG as a function of an instantaneous base current I DC_RG,act for the reference gas RG, whereby - an instantaneous electrical power P DC_RG,act of the laser source assigned to the gas absorption line for the reference gas RG is ascertained from the instantaneous base current I DC_RG,act and the instantaneous internal resistance R I_RG,act, - an instantaneous electrical power P DC_ZG,act of the laser source assigned to the gas absorption line for the target gas ZG as the sum from the instantaneous electrical power P DC_RG,act and the power difference ΔP DC,cal is determined, - the assigned instantaneous base current I DC_ZG,act is calculated from the instantaneous electrical power P DC_ZG,act of the laser source, taking the instantaneous internal resistance R I_RG,act into consideration. - the base currents I DC_RG,cal and I DC_ZG,cal assigned to the gas absorption lines for the reference gas RG and for the target gas ZG are established, - the associated electrical powers P DC_RG,cal and P DC_ZG,cal of the laser light source are determined from the base currents I DC_RG,cal and I DC_ZG,cal as well as from the associated internal resistances R I_RG,cal and R I_ZG,cal, - a power difference ΔP DC,cal is found by means of the electrical powers P DC-RG,cal and P DC_ZG,cal and this or one or more equivalent variables are stored in the measuring system, - an instantaneous electrical power P DC_RG,act of the laser source assigned to the gas absorption line for the reference gas RG is ascertained from the instantaneous base current I DC_RG,act and the instantaneous internal resistance R I_RG,act, - an instantaneous electrical power P DC_ZG,act of the laser source assigned to the gas absorption line for the target gas ZG as the sum from the instantaneous electrical power P DC_RG,act and the power difference ΔP DC,cal is determined, - the assigned instantaneous base current I DC_ZG,act is calculated from the instantaneous electrical power P DC_ZG,act of the laser source, taking the instantaneous internal resistance R I_RG,act into consideration.