Abstract

In this paper a compact, yet sensitive gas detection system based on a modulated, tunable thulium-doped 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 (${\nu }_1+2{\nu }_2+{\nu }_3$) of ${\mathrm{CO}}_2$ 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 ${\mathrm{CO}}_2$, have been monitored through absorption spectroscopy techniques. The measured minimum detectable concentration of ${\mathrm{CO}}_2$ obtained using the system shows that it is quite capable of detecting trace gas at the ppm (parts in ${10}^6$) 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.

© 2013 Optical Society of America

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