A Unique Split Laser System for Environmental Monitoring

Environmental monitoring, i.e., the assessment of air,  water and soil quality, is highly important to oil and gas exploration companies, landowners, regulatory agencies, municipalities and any organization measuring emissions and pollutants.  The majority of monitoring technologies, however, are expensive and labor intensive, often requiring sample collection and preparation (i.e., external lab analysis) which can dramatically alter the sample and its inherent components.  Of those technologies that do allow for in situ analysis, few are amenable to measurements under harsh conditions, such as high temperature and/or pressure.

Laser Induced Breakdown Spectroscopy (LIBS), an atomic emission spectroscopy, offers solutions to the drawbacks of conventional environmental monitoring technologies.  It provides rapid and relatively simple qualitative and quantitative elemental analysis.  Significantly, this analysis can be accomplished without the need for sample collection or preparation. Moreover, LIBS can be applied to in situ measurements of gases, liquids and solids, making it amenable to the monitoring of air, water and soil.  The majority of available LIBS systems, however, are large and complex, employing aboveground, laboratory-scale lasers.  Furthermore, the design of current systems and the complexity of their components do not allow for monitoring under extreme conditions, such as high temperature and pressure.

NETL researchers have designed a LIBS system fully adaptable to field use and capable of measurements in harsh environments.  The system has been designed to be portable, with a minimal number of optical components, no moving parts and no electrical connections, which should translate into far lower production costs than competitive devices.  In addition, unlike competing LIBS systems which employ actively Q-switched lasers, NETL’s system utilizes a passively-switched laser, providing the same degree of precision timing as the actively-switched output with fewer components and a lower cost laser system. The NETL system also employs a unique split laser design.  Conventional LIBS analysis requires complete laser systems to deliver a high peak pulse to the sample, incompatible with the use of optical fibers which are ideal for at-a-distance monitoring.  To avoid fiber optic damage, NETL’s system employs a remotely-positioned laser diode pump capable of generating a peak power of only a few hundred watts as compared to the megawatts produced by conventional systems.  The low peak pulse is delivered via a fiber optic cable to a remotely-located solid state laser where the high peak pulse necessary for analysis is produced. Significantly, this unique dual laser arrangement coupled with solid state optics permits monitoring of even severe downhole environments while avoiding system damage.

The split laser design also provides for multipoint analysis, allowing multiple lasers to be distributed over a broad area, ideal for applications such as the detection of CO₂ leakage from an injection basin.  Adding to the system’s flexibility, with few modifications the same system can also be used to provide output for Raman analysis, permitting the identification of organic compounds such as methane.  Thus, one system can be designed to be used for both LIBS and Raman investigations.  For example, the system can be used above ground or downhole to directly monitor CH₄ via Raman analysis and detect changes in groundwater ions via LIBS.