Читать книгу Geophysical Monitoring for Geologic Carbon Storage - Группа авторов - Страница 48

The development of field deployable FMS instruments started with the construction of an in situ instrument similar to the one depicted in Figure 3.3. The instrument uses a New Focus tunable diode laser (TDL) that scans over the 1,604–1,609 nm CO₂ absorption band. A Stanford Research Systems DS345 function generator was used to directly modulate the TDL at 2 GHz. The laser is fiber optically coupled to an Infrared Analysis, Inc., 8 m long multipass White cell. Air samples containing CO₂ are pumped into the White cell for analysis. The laser beam exits the White cell, is launched into a second optical fiber that directs the laser into a New Focus detector. The output of the director is filtered and amplified with a Stanford Research Systems SR560 before being recorded on a PC.

Figure 3.3 The in situ FMS instrument built at Los Alamos National Laboratory enclosed in a weatherproof case for field deployment.

An open‐path remote instrument was developed using the same optical system discussed for the in situ system above. The same model New Focus TDL was fiber optically coupled to a 5x beam expander used to collimate an enlarged beam. The modulated beam was directed to a retroreflector placed up to hundreds of meters away from the beam expander. The returned laser beam was collected with a second beam expander, coupled to a second optical fiber and onto the New Focus detector.