Thirty-two people died in Seoul, South Korea, on Oct. 21, 1994, when the Seongsu Bridge over the Han River unexpectedly collapsed during the morning rush hour. The catastrophe occurred because of structural wear and tear to the bridge’s steel structure that had gone undetected. While not common-thankfully-such events do serve to underscore the challenges associated with maintaining the safety of an aging civil infrastructure. Of course, the need for structural integrity is not limited just to bridges but applies also to tunnels, aircraft, walls, and boats-and systems to monitor strain, temperature, humidity, and other important indicators of what’s happening beneath the surface of these structures have been around for decades. Most recently, innovative optical sensing systems have demonstrated a unique set of capabilities in this regard and many new structures as well as a few ancient ones are reaping the benefits of these developments (see p. 62).
Continuing innovation brings an abundance of novel developments in sources, detectors, and other components, meanwhile, creating new opportunities for optics and photonics. Infrared detector arrays, for instance, have increased exponentially in size (and resolution) as they benefit from the application of semiconductor-processing techniques to their manufacture-this year IR arrays should exceed 16 megapixels in size (see page 81). In the medical field, cellular visualization of the human retina in vivo is now possible by combining optical coherence tomography with adaptive optics that compensate for the eye’s optical aberrations (see p. 86). And as compact and powerful new lasers have emerged, they are bringing about a revival in laser-induced breakdown spectroscopy (see p. 94). Such “real world” developments are typically preceded by years of basic research-like the innovation being applied to the search for a practical silicon laser, which is making noteworthy strides (see p. 90).
By the way, after two years and eight months for repairs, the Seongsu Bridge was reopened in July 1997.