A-scan Raman microspectroscopy based on remote focusing with a planar mirror

Conventional depth-resolved Raman microspectroscopy relies on point-by-point axial scanning, which is slow and increases the risk of photodamage. To address this issue, we have developed A-scan Raman microspectroscopy, named after A-scan in ultrasound imaging, which is based on remote focusing with a planar mirror that maps the axial information of a sample into the lateral dimension for snapshot depth-resolved Raman measurements. Raman spectra from 21 distinct depth positions are captured simultaneously in a single snapshot. The system was validated on ex vivo porcine samples and then used in ex vivo mouse skin experiments for drug penetration characterization, demonstrating a more than 40-fold acceleration in depth-resolved Raman spectra acquisition compared with that of a confocal Raman microscope.