Sensitive detection of CO2 implementing tunable thulium-doped all-fiber laser

In this paper a compact, yet sensitive gas detection system based on a modulated, tunable thuliumdoped fiber laser in the 2 mu m wavelength region is reported. The laser operating wavelength range centered at a wavelength of 1.995 mu m has been selected to access the R(50) transition (nu(1) + 2 nu(2) + nu(3)) of CO2 based on its line strength and to achieve isolation from interfering high-temperature water absorption features. The laser linewidth and tuning range are optimized accordingly. The modulation of the fiber laser, achieved through pump source modulation and a locking detection mechanism, has been utilized to stabilize the laser system and therefore to create a compact gas sensor with high sensitivity. The absorption spectrum, as well as the line strength and the concentration level of CO2, have been monitored through absorption spectroscopy techniques. The measured minimum detectable concentration of CO2 obtained using the system shows that it is quite capable of detecting trace gas at the ppm (parts in 106) level. The stable laser performance achieved in the sensor system illustrates its potential for the development of practical, compact, yet sensitive fiber-laser-based gas sensor systems. (C) 2013 Optical Society of America