Mid-infrared quantum cascade laser-based structured illumination microscope

We demonstrate, for the first time to the best of our knowledge, the implementation of Spatial Frequency Modulated Imaging (SPIFI) microscopy in the mid-infrared region using a Quantum Cascade Laser (QCL) source. Hyperspectral imaging in the mid-infrared (3–20 μm) enables chemically specific mapping and structural imaging based on molecular contrast, which is otherwise inaccessible in the visible or near-infrared region. But mid-infrared microscopes are often limited by slow raster scanning and costly detector arrays. Our approach uses spatial frequency-encoded structured illumination and a low-cost single-pixel mid-infrared detector to acquire hyperspectral images in transflection mode. The system—structured illumination single-pixel imaging system in the mid-infrared—provides a practical trade-off between speed and complexity, offering acquisition speeds comparable to selected QCL-based point-scanning implementations, while maintaining a simple, cost-effective optical design utilizing off-the-shelf components. We present a preliminary resolution measurement as well as absorption images of coronal sections of a mouse brain at both 6 and 7 μm, demonstrating chemically selective contrast and robust image formation suitable for future high-resolution and compressive implementations.