Mid-Infrared Hyperspectral Single-Pixel Microscopy with a Quantum Cascade Laser

A hyperspectral mid-infrared (MIR) microscope utilizing single-pixel imaging (SPI) technology is demonstrated. The system integrates a tunable (8.3 µm - 11.1 µm) MIR quantum cascade laser (QCL) and a modified micro-opto-electro-mechanical digital micromirror device (DMD) for spatial light modulation. As a part of the system's design, diffraction on the DMD chip is experimentally analyzed. Based on this analysis, the first diffraction order was selected for an optimal optical configuration thus providing high modulation contrast, which is critical for SPI. The spatial resolution of the developed microscope was evaluated using a reflective resolution test target, which verified resolution well beyond 24.8 µm at 10.1 µm wavelength. Obtained spectra, which are limited in bandwidth (9.80 µm - 10.42 µm) due to aperture constraints, are validated by characterizing a 8 µm-thick polypropylene (PP) foil and identifying PP in a polymer multilayer microtome section. Fourier-transform infrared (FTIR) spectra were used for reference. The microscope showcases SPI's potential for efficient chemical analysis, offering rapid hyperspectral IR imaging.