Portable Mid-IR Spectrometer

We describe a mid-IR spectrometer by combining a commercial thermal imaging camera with a Diesel engine glow-plug and a micromachined hyperspectral filter. Our hyperspectral mid-IR filter consists of two silicon/air mirrors that form an optical cavity. A small angle between the two high-reflectivity mirrors provides us with a gradual variation of the cavity resonance peak and we obtain a position-dependent transmission filter. The linear variation of resonance frequency with position enables the ~40,000 pixels in the thermal bolometer camera to be converted into an optical multichannel spectrometer. Filters are made of multiple layers of silicon and air, and the high refractive index and transparent properties of silicon in the mid-IR region provide a wide free spectral range of up to 10 micrometers. Different wavelengths can be assigned to each pixel in the microbolometer array, enabling rapid spectral acquisition in our compact spectrometer. This allows us to measure the mid-IR spectra of various types of polymers, biomolecules and medications in a compact system. Here we show mid-IR molecular absorption spectra from different materials measured with this spectrometer and compare them to Fourier-Transform Infrared Spectroscopy (FTIR) results.