A gas cell assembly and applications of the gas cell assembly in absorption spectroscopy. An example gas cell assembly includes a gas cell body with an inlet for receiving a gas sample from a gas source; a first and a second end portions that allow optical transmission into and out of the body, the second end portion being substantially opposite from the first end portion; and a channel providing a path for the gas sample and optical beam(s) between the first end portion and the second end portion. The gas cell assembly also includes reflective surfaces outside the body to receive versions of the optical beams from the body and to reflect each version of the incident beam towards the body. A detector, then, receives a last reflected beam and transmits a corresponding data signal to a processing unit for analyzing the gas sample based on the data signal.