Experimental configuration: The OGE cell inside the cavity has Brewster windows to reduce losses. The C12 laser incident on the OGE cell provides a “C12 signal” that is used for normalization of the C14 signal. The shutter inside the laser cavity is for modulating the 14CO2 laser. M1: High reflective mirror & grating, M2: 85% reflective output coupler, M3: Gold plate mirror, PS: Pressure Sensor, FC: Flow Controller, RGA: Residual Gas Analyzer, DAQ: Data Acquisition Board