Laser-spectroscopic, ultra low volume and low level carbon monoxide sensor

A low level optical carbon monoxide sensor utilizing a 2.3 μm surface-emitting laser and a hollow capillary fiber as gas "pipe" and waveguide is developed and practically demonstrated for the first time. Tunable diode laser spectroscopy based sensors have advantages like low cross sensitivity and nearly fail-safe operation. Additionally, fiber-based optical cells are a highly attractive alternative to ordinary multipass cells due to strongly simplified alignment and dramatically lowered sample volume. By vibration of the fiber an absorbance resolution comparable to ordinary cells, i.e. 10^-5, is achieved. A 17 fold improvement in concentration resolution is obtained with a 3 m fiber (170 ppb, 1 Hz) compared to a single-reflective cell and the needed sample volume is simultaneously lowered by several orders of magnitude to 1.3 ml. This clearly demonstrates the potential of laser spectroscopic hollow capillary fiber based sensors. An additional significant sensitivity improvement is expected by using even longer fibers.