Photonic-Crystal-Fiber-Coupled, Hand-Held, Polarization-Resolved Second-Harmonic-Generation Microscope for In Vivo Visualization of Dermal Collagen Fibers in Human Skin

Second-harmonic-generation (SHG) microscopy is a powerful tool for in vivo monitoring of collagen fibers in human skin. Furthermore, polarization-resolved SHG microscopy can provide additional insights regarding the direction of collagen fibers, i.e., collagen fiber orientation. However, their practical use in the dermatological field is still limited due to the bulky and complicated setup. In this paper, we constructed a photonic-crystal-fiber (PCF) coupled, hand-held polarization-resolved SHG microscope for in vivo monitoring of collagen fibers in human skin. Fiber delivery of ultrashort pulse light was achieved without significant change of the linear polarization by a large-mode-area PCF, whereas the SHG microscopy setup was enclosed into a hand-held probe head. The combination of PCF with the hand-held probe head largely enhances the flexibility of measurement sites in the human skin.