Field Monitoring of Gases Using III-V Semiconductor Diode Laser Technology

III-V semiconductor diode lasers can be used to make accurate measurements of the concentrations of gases. In this paper the field of trace gas detection using III-V semiconductor diode lasers will be reviewed with an emphasis on suitable applications of this technology in pipeline monitoring. III-V semiconductor diode lasers emit light in the near infrared (NIR) with wavelengths ranging from 1 to 2 μm. Many molecules have absorption lines in this spectral range which makes them contenders for detection with diode laser technology. Molecules relevant to the pipeline industry that can be detected using diode laser systems include H2S, C2H4, C2H2, HF, CO2, CO, O2, NH3, HC1, NO, NO2, HCN, H2O and CH4. Diode laser detection systems may be well suited for many pipeline related applications. Portable field-screening detection systems may be possible, such as hand-held systems which can be used to pinpoint leaks for compressor station inspection. Airborne (∼200 km/h) and mobile (∼40 km/h) systems which can be used for pipeline and urban area inspection may also be feasible. Stationary systems can be integrated into pipeline systems to provide real-time remote gas monitoring for Supervisory Control and Data Acquisition (SCADA) systems. Detection sensitivities of parts per million (ppm) or better are achievable for many gases. A single diode laser detector can be designed to detect more than one gas leading to versatile multipurpose systems. As III-V diode laser based gas detection systems exploit the same technologies as the highly successful telecommunications industry they have the potential to be low in cost, reliable, and easy to operate and maintain. We will present an overview of state-of-the-art III-V diode laser detection systems. System performance will be evaluated and the usefulness of these types of detection systems will be demonstrated.