Optical gas sensor device and method for determining the concentration of a gas

A gas sensor device for determining a concentration of a gas to be detected, which gas absorbs light of a measurement wavelength that is characteristic of the gas in an infrared light region, the gas sensor comprising:

• a light detector;
• a light emission device adapted for emitting measurement light of the measurement wavelength (I) into a solid angle region of a light absorption path that extends through the gas to be detected, and (II) to an object that (a) is located outside of the gas sensor device and (b) at least partially reflects the measurement light to the light detector, wherein:
• the light absorption path extends outside of the gas sensor device, from the light emission device to the object, and, by the reflection, from the object to the light detector;
• and
• the light detector is adapted for measuring an intensity of at least one component of the measurement light that has propagated through the light absorption path;
• and
• a component configured to determine a length of the light absorption path of the measurement light from the light emission device to the light detector.