Umplfln 40xw

As shown in Figure S1a, our OCT system is based on a commercial OCT instrument (Ganymede OCTP-900, Thorlabs) and the light source is centered at 910 nm with a bandwidth of 200 nm (EXR-9 continuum laser, NKT Photonics). The Gaussian beam diameter before entering the objective is 4.6 mm (1/e²). Its acquisition rate is 30,000 A-scans/s. The imaging depth is 2 mm in air or 1.5 mm in water with 1024 pixels, thus the axial pixel size is about 2.0 μm in air and 1.5 μm in water, and the experimental axial resolution is 3 pixels (fwhm in linear scale). It is equipped with a 40× water immersion objective (UMPLFLN40XW, Olympus), offering a FOV of 0.5 mm × 0.5 mm with a good image quality. The laser power entering the objective aperture is controlled below 10 mW. For the experiments in Figures 4–6, pixel number in both the X and Y directions was chosen as 512, and FOV was set as 0.125 mm × 0.125 mm for bead imaging and 0.25 mm × 0.25 mm for skin imaging, respectively. During image reconstruction, a 2D Gaussian filter with a standard deviation of 2 pixels was applied for every XY image to reduce speckle noises. All OCT images were presented in log10 scale.