Enabling mid-IR spectroscopic sensing: MEMS-based high-speed FT-IR compact spectrometers

Despite their inherent advantages, the number of practical applications of spectroscopic direct chemical mid-IR sensors is still limited. This is largely due to a lack of suitable spectrometers that are at the same time compact and robust, fast and sensitive, and cover the relevant spectral range at adequate resolution. To resolve this, the concept of using micro-mirrors in FT-IR spectrometers has been put into practice. Combining specifically designed components, in particular a large aperture translatory MEMS mirrors with large oscillation amplitude, a miniaturised high-power IR source, a fast HgCdTe detector, and a dedicated, fully integrated close-loop mirror control driving the MEMS element reliably at its optimum, resulted in the first practically applicable prototype of a MEMS-based high-speed FT-IR spectrometer operable under real-world conditions. Covering the range 5,400-700 cm^-1 (1.8-14 μm) at a spectral resolution of 8 cm^-1 and a maximal time resolution of 0.5 ms, this development is expected to provide the central element for a new generation of IR-spectroscopic direct chemical sensors.