Background noise suppressed high-throughput mid-infrared photothermal microscopy via pupil engineering

Mid-infrared photothermal microscopy (MIP) has been a promising chemical imaging technique for functionality characterization of biological and pharmaceutical specimens owing to its enhanced resolution and high-specificity. Recently developed wide-field MIP modalities drastically improved the imaging speed and thus enabled high-throughput imaging. However, the sensitivity of the wide-field MIP technique has been limited by shot-noise of background photons. Here, we demonstrate a dark-field MIP modality to allow 4-fold signal-to-noise ratio improvement. Our technique is based on selectively blocking the reflected light. Simulation and experimental results are both provided, and they are consistent with each other.