Reflection matrix microscopy at 1.6 µm wavelength for label-free deep-tissue imaging

Multiple light scattering sets the depth limit of optical microscopy in biological tissue. Reflection matrix microscopy with the multiple-scattering tracing algorithm can overcome this scattering, but its application has so far been limited to wavelengths of 1.3 μm and below. Here, we develop, to our knowledge, the first reflection matrix microscope operating at 1.6 μm. By integrating it with a 1.3 μm channel into a single dual-wavelength system that isolates the wavelength as the principal variable, we quantitatively demonstrate that 1.6 μm markedly outperforms 1.3 μm. The reconstructed phase distortion in the mouse skull is weaker at 1.6 μm and the isoplanatic patch about 1.67 times larger. We resolve osteocytes lying beneath the strongly scattering bone marrow of the skull, a target unreachable at 1.3 μm.