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

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 (ν1+2ν2+ν3) 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 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.

All-fiber tunable ring laser source near 2 μm designed for CO2 sensing

“…DFB lasers as well as fiber Bragg grating-based fiber laser sources are used for sensing applications as they provide a narrow linewidth stable output; however they have limited tunable range (to a few nm). A tunable modelocked erbium-doped fiber laser with dispersion tuning near 1530 nm and 1560 nm [14], CW lasers with tunable filters [15,16] as well tuning with relaxation and compression of FBGs near the near 2 μm region have been demonstrated earlier [17,18]. The FBG based lasers provide limited tunability of a few nm, whereas the fiber lasers with larger tunable ranges of > 100 nm usually employ expensive filters in the experimental setup.…”

Dual-band Tm3+-doped tellurite fiber amplifier and laser at 1.9 μm and 2.3 μm

“…The maximum pump power launched in 100-μm cladding was ~2.6 W. The low efficiency was explained by non-optimal optical elements available to us. However, the achieved laser powers are sufficient for some applications, for example, gas detection (CH 4 at 2.3 μm 2  or CO 2 at 1.95 μm 38 ).…”

Gas Sensor Design Based on a Line Locked Tunable Fiber Laser and the Dual Path Correlation Spectroscopy Method

“…Another light source option for LL-TLAS sensing in the near infrared (NIR) region are fiber lasers, since these can provide narrow line width emissions and are relatively low cost because these can be implemented with standard communication components [4]. These lasers can be used to detect gases such as acetylene (C 2 H 2 ), hydrogen iodide (HI), ammonia (NH 3 ), carbon monoxide (CO) and carbon dioxide (CO 2 ) [11][12][13]. Lasers that will be used in TLAS applications must be able to be continuously tuned over the spectral range where the ro-vibrational absorption lines occur.…”