Polarimetric infrared spectroscopic imaging using quantum cascade lasers

Infrared spectroscopic imaging has emerged as a powerful label-free diagnostic tool to study the molecular composition and organization in biological tissues and cells. We report infrared spectroscopic imaging using polarized light to study differential absorption of plane-polarized light by an oriented sample to detect valuable information, such as, birefringence and dichroism. For instance, the organization of collagen, specifically fiber orientation and alignment, is crucial in understanding the progression and metastasis of cancer. Recent advancements in the development of Quantum Cascade Lasers (QCL) sources have opened new avenues for high SNR measurements in the field of IR spectroscopy. In addition, QCL sources are intrinsically polarized and orientation information can be obtained at discrete frequencies with different polarization orientations, allowing much faster acquisition than a corresponding FT-IR approach. We demonstrate improved performance in terms of fast and comprehensive polarimetric image acquisition and analysis using custom-built QCL microscope and evaluate its impact on applications by analyzing the important spectral bands of surgical tissue sections.