Multimodal nonlinear optical imaging of unstained retinas in the epi-direction with a sub-40 fs Yb-fiber laser

Ultrafast lasers have potential use in ophthalmology for diagnoses through non-invasive imaging as well as for surgical therapies or for evaluating pharmacological therapies. New ultrafast laser sources, operating at 1.07 μm and sub-40 fs pulse durations, offer exciting possibilities in multiphoton imagining of the retina as the bulk of the eye is relatively transparent to this wavelength, three-photon excitation is not absorbed by DNA, and this wavelength has a greater penetration depth compared to the commonly used 800 nm Ti:Sapphire laser. In this work, we present the first epi-direction detected cross-section and depth-resolved images of unstained isolated retinas obtained using multiphoton microscopy with an ultrafast fiber laser centered at 1.07 μm and a ~38 fs pulse duration. Spectral and temporal characterization of the autofluorescence signals show two distinct regions; the first one from the nerve fiber layer to the inner receptor layer, and the second being the retinal pigmented epithelium and choroid.