Nitrogen Dioxide Detection in Hollow Core Fiber With Long Dynamic Range

We present a compact nitrogen dioxide (NO ₂ ) detection system using a wavelength-tunable single-frequency blue laser in hollow core fiber with absorption dips and photoacoustic (PA) signals. The molecular NO ₂ has a harmful impact on human health, such as lung function and visibility decreasing. It even inhibits plant growth. How to detect NO ₂ with low detection limit and long dynamic range is a vital issue. However, an ultralow detection limit sometimes means these devices cannot work well under high concentration level. Compared with ultralow detection limits, long dynamic range was considered more important for the fields of agricultural and environmental engineering. So, we combined two detection methods in one optomechanical design: PA and direct absorption spectroscopies. The interaction between the NO ₂ molecules and lights in hollow core fiber can be effectively increased. High light absorption induced fast heating process. The ppb detection limit can be realized by the PA signals. But due to the mechanic design, the nonlinearity of PA signals can be found at high concentration level. Compared with PA, the direct absorption spectroscopy can be extended to high concentration level. Long dynamic range, i.e., 57 dB, can be achieved with this one optomechanical design. The ppb detection limit of PA signals can also be realized. The work range for NO ₂ concentration can be from 2 ppb to 1000 ppm. The long-term instability was estimated as 0.11%.