Development of a Compact and Robust Mid-Infrared Spectrometer by Using a Silicon/Air Hyperspectral Filter

The molecular absorption spectrum in the mid-infrared (mid-IR) region is typically measured by Fourier-transform infrared spectroscopy (FTIR). Such spectrometers require complex and delicately aligned interferometers, which increases their size and cost. Here, we present an alternative compact mid-IR spectrometer, which uses a variable mid-IR filter with a gradual change of cavity length between two silicon/air dielectric mirrors. When combined with a modern uncooled thermal imaging camera, hyperspectral filtering can provide a powerful solution for the miniaturization of mid-IR spectrometers. By using the hyperspectral filter, light from a broadband light source can be dispersed and assigned to individual pixels of a microbolometer array of the thermal imaging camera. This technology offers an inexpensive and compact mid-IR spectrometer design with no moving parts and rapid acquisition time.