A portable spectrophotometric system for detecting one or more target
substances. In a representative embodiment, a system of the invention has
an optical grating, an array of photo-detectors, and a MEMS device having
a movable plate positioned between the grating and the array. Light
transmitted through a gaseous sample is dispersed by the grating and is
imaged onto the movable plate, which has a plurality of openings
corresponding to selected infrared absorption lines of the target
substance. A small-amplitude oscillation is imparted onto the plate such
that the openings periodically move in and out of alignment with the
corresponding intensity features in the image, which modulates electrical
signals generated by the corresponding photo-detectors. A lock-in signal
processor analyzes the modulation pattern by comparing it to the pattern
expected in the presence of the target substance. When a positive
correlation between the patterns is established, the system warns the user
about the presence of the target substance.
