Optical gas sensor for determining a gas concentration, having - a measurement cell for receiving the gas, which comprises a light channel extending along a longitudinal direction, - a radiation source for emitting electromagnetic radiation onto the gas located in the measurement cell, wherein the radiation source is arranged in a light entrance region of the measurement cell and emits radiation in the direction of the light channel, - at least one detector, which serves for detecting at least parts of the electromagnetic radiation that have passed through the gas, wherein the at least one detector is arranged in a light exit region, wherein - at least one entrance-side deflection element (16; 116; 216; 316) which deflects the radiation that is incident thereon both directly and indirectly via a reflective inner side of the measurement cell (10; 110; 210; 310) along the longitudinal direction of the light channel (11; 111; 211; 311) in the direction of the at least one detector (15.1, 15.2; 315) is arranged in the measurement cell (10; 110; 210; 310) and the at least one entrance-side deflection element (16; 116; 216; 316) is embodied to be shaped like a pyramid and is arranged on a longitudinal side of the measurement cell (10; 110; 210; 310), wherein the tip of the pyramid is oriented in the direction of the radiation source (12; 112; 212; 312), and/or - at least one exit-side deflection element (17.1, 17.2; 417) which deflects the radiation propagating along the longitudinal direction of the light channel (11; 411) both directly and indirectly via a reflective inner side of the measurement cell (10; 410) in the direction of the at least one detector (15.1, 15.2; 415) is arranged in the measurement cell (10; 410) and the at least one exit-side deflection element (17.1, 17.2; 417) is embodied to be shaped like a pyramid and is arranged on a longitudinal side of the measurement cell (10; 410), wherein the tip of the pyramid is oriented in the direction of the detector (15.1, 15.2; 415). - a measurement cell for receiving the gas, which comprises a light channel extending along a longitudinal direction, - a radiation source for emitting electromagnetic radiation onto the gas located in the measurement cell, wherein the radiation source is arranged in a light entrance region of the measurement cell and emits radiation in the direction of the light channel, - at least one detector, which serves for detecting at least parts of the electromagnetic radiation that have passed through the gas, wherein the at least one detector is arranged in a light exit region, wherein - at least one entrance-side deflection element (16; 116; 216; 316) which deflects the radiation that is incident thereon both directly and indirectly via a reflective inner side of the measurement cell (10; 110; 210; 310) along the longitudinal direction of the light channel (11; 111; 211; 311) in the direction of the at least one detector (15.1, 15.2; 315) is arranged in the measurement cell (10; 110; 210; 310) and the at least one entrance-side deflection element (16; 116; 216; 316) is embodied to be shaped like a pyramid and is arranged on a longitudinal side of the measurement cell (10; 110; 210; 310), wherein the tip of the pyramid is oriented in the direction of the radiation source (12; 112; 212; 312), - at least one exit-side deflection element (17.1, 17.2; 417) which deflects the radiation propagating along the longitudinal direction of the light channel (11; 411) both directly and indirectly via a reflective inner side of the measurement cell (10; 410) in the direction of the at least one detector (15.1, 15.2; 415) is arranged in the measurement cell (10; 410) and the at least one exit-side deflection element (17.1, 17.2; 417) is embodied to be shaped like a pyramid and is arranged on a longitudinal side of the measurement cell (10; 410), wherein the tip of the pyramid is oriented in the direction of the detector (15.1, 15.2; 415).