Sensing with more sensitivity

Environmental sensing and monitoring is rather vague terminology for an extremely broad and ever growing field that encompasses a vast array of detection and analysis techniques, from the use of laser-induced breakdown spectroscopy (LIBS) for remote materials analysis on the planet Mars, to real-time on-location car-exhaust monitoring here on Earth. Many of these techniques are based on emission or absorption of light, so photonics and optics play a pivotal role (see p. 40).

And it’s a role that’s growing rapidly as researchers expand the range of available photonic sources and detectors. Quantum-cascade lasers, for instance, offer compact and tunable sources of mid-infrared light and have spawned novel gas analyzers for industrial pollution monitoring and trace gas detection as well as noninvasive molecular sensing for standoff detection of explosives and disease. Meanwhile development continues on other novel sources such as lasers based on new materials. Doped zinc sulfide devices, for instance, emit tunable infrared output in the 1.95 to 2.85 µm range (see p. 50).

On the detection front, sensors for biological and medical applications–such as those capable of detecting specific biological agents–are currently getting a lot of attention. Surface-enhanced Raman spectroscopy (SERS) is a promising technique for highly sensitive, molecule-specific detection that’s gradually moving from the research arena into real-world applications as a variety of novel implementations seek to make the technique stable and reproducible in the field. In one realization a metallic nanowire is cast into a metallic film to provide a SERS platform (see p. 36).

Another facet of sensing and monitoring technology is imaging. Here too, technology advances are leading to imagers with increased capabilities. Multispectral imagers collect image information at several wavelengths–some of them typically beyond the range of the human eye. In the medical arena, handheld multispectral imagers are being explored as tools to unambiguously detect the severity of body trauma, such as bruises and could become an invaluable part of an emergency doctor’s toolbox (see www.laserfocusworld.con/350987). And researchers in Germany and Australia have come up with a “wide-angle lens” that provides an unoccluded 260° field of view by combining two optical systems–one refractive and one catadioptric. The resulting panoramic images–like the one shown on this month’s cover–are quite remarkable (see p. 17).