Delivering reliable operation in extreme conditions, the metal jacket series of gold- and aluminum-coated optical fibers from Fiberguide Industries Inc. has proved effective in a number of scientific applications, including Raman spectroscopy. They were originally developed for ultrahigh-reliability telecommunications. Their metal coating preserves their mechanical strength and provides resistance against the static fatigue caused by long-term tensile loading. The coated fibers can withstand a wide range of temperatures: aluminum from –269 to 400 °C, and gold from –269 to 700 °C. Gold or aluminum coating can be applied on continuous lengths to a wide variety of multimode, step index, graded index and single-mode fibers. Core to clad ratios of 1:1, 1:2 and 1:4 are available with numerical apertures of 0.12 and 0.26. Nonstandard sizes also can be manufactured upon request.