The method includes guiding a light beam to a first optical path, the light beam being attenuated to an attenuated light beam and detecting a first value indicative of a first intensity of the attenuated light beam. The method further includes generating a last light pulse, dissociating at least part of the gas compound molecules (optionally excited) or dissociated parts thereof (optionally excited) on the first optical path to first part atoms, molecules, ions, or radicals, and to another part using the last light pulse, the light beam being further attenuated by absorption to the first part atoms, molecules, ions, or radicals on the first optical path. The method further includes detecting a second value indicative of a second intensity of the attenuated light beam and determining, using the first and second values, the gas compound content of the gas mixture. A gas compound measuring device measures uses the method.