Chemical imaging, especially mid-infrared spectroscopic microscopy, enables label-free biomedical analyses while achieving expansive molecular sensitivity. However, its slow speed and poor image quality impede widespread adoption. We present a microscope that provides high-throughput recording, low noise, and high spatial resolution where the bottom-up design of its optical train facilitates dual-axis galvo laser scanning of a diffraction-limited focal point over large areas using custom infinity-corrected objectives. The data quality enables applications of modern machine learning and capabilities not previously feasible. Distinct from conventional approaches that focus on morphological investigations or immunostaining, this development makes label-free imaging of minimally processed tissue practical.
Quantum cascade lasers (QCLs) have presented a new chapter for the development of infrared spectroscopy for its high throughput and ability to tune to absorption bands of interest. However, compared to conventional thermal sources, the output stability of QCLs is a limiting factor. Specifically, the noise associated with pulse-to-pulse instability is of specific concern as we design faster and more sensitive spectrometers. Here, we demonstrate a dual-detector approach to reference measurements with the intensity illuminating the sample in real-time per individual laser pulse. We integrate this concept into our custom point-scanning confocal IR microscope. Results show double the SNR and a 10-fold shorter response time with the proposed method versus a single detector approach, all while being lock-in amplifier free. We characterize the controllable parameters and discuss the trade-offs required for a unified system capable of collecting high-quality point spectra as well as whole-slide spectral imaging.
Infrared spectroscopic imaging combines the ability to record molecular content with the ability to visualize chemistry in its spatial diversity. Given the need to record a significantly larger quantity of data than a typical microscopy image (MB vs. GB) and the extensive bandwidth of the spectra (~10 m), trade-offs often have to be made between the closely related considerations of signal to noise ratio, spatial-spectral coverage, resolution and optical arrangements. Here, we present a path from rigorous theory to modeling and design to realizing the advantages offered by new ideas on fundamentally changing these trade-offs. We first describe a new microscope design for increased speed and rapid coverage that is useful for biomedical and clinical tissue imaging. Next, we describe a configuration to measure chirality in samples that promises higher spectral information that present methods. Finally, we present a new approach to nanoscale IR imaging that provides greater fidelity and speed at unprecedented levels of signal to noise ratio. Finally, we show how emerging machine learning approaches can further augment these advances. For each instrumentation advance, examples of use cases will be presented.
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