Enabling 3D refractive index tomography in laser scanning microscopy with a simple tape-on detector

We introduce quantitative scanned oblique back-illumination microscopy (qsOBM) for laser scanning microscopes (LSMs), enabling quantitative three-dimensional refractive index (RI) tomography in thick scattering samples. By exploiting the reciprocity of light scattering, the established camera-based qOBM reconstruction framework is extended to a scanning implementation. Experimentally, qsOBM is realized with a slide-mounted four-quadrant photodetector requiring only minimal optomechanical modification of a conventional LSM. We demonstrate quantitative RI imaging and multimodal qsOBM/epi-detected second-harmonic generation (SHG) microscopy of type I collagen and adipose tissue in chicken muscle. The resulting RI tomograms provide label-free volumetric morphological information that complements SHG microscopy and expands the capabilities of existing LSM platforms for multimodal tissue imaging.