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 μm wavelength region is reported. The laser operating wavelength range centered at a wavelength of 1.995 μm has been selected to access the R(50) transition (?1 + 2?2 + ?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.