Application of a super-luminescent diode coupled with an interference filter for mixed gas sensing

Laser-based spectroscopic techniques are very attractive methods for trace gas, environmental and industrial monitoring. By employing narrow spectral-width tunable coherent light sources, a single absorption line of the substance to be analyzed can be probed with a laser, avoiding interference signals from other species. Here we report a difference frequency generation (DFG) source in mid-infrared region using a tunable laser (825 - 870 nm) and a fixed wavelength diode laser (1060 nm) in combination with a PPLN having single period. Application of the approach for carbon dioxide (CO2) monitoring in air was studied. Many gas sensing applications do not require extreme sensitivities up to ppb order and in this case, super-luminescent diodes (SLD) are also of great interest. They are commonly produced in the spectral range of optical fibers telecommunications (1.3 - 1.7 m), where overtone vibration bands of many gas molecules of interest. As a typical example, measurements of ammonia (NH3) trace gas were studied for combustion measurement applications. A novel approach of using fiber-coupled SLD along with an interference filter can also be considered for such application to avoid influence of water vapor (H2O). The interest of this system consists in the possibility to detect several species with a single instrument. © 2011 Published by Elsevier B.V.