Figure 6.

SHG image of an optical section taken about 100 µm below the cut surface of the corneal physical section. An area (cropped from a larger image) of approximately 6 × 4 images each 512 × 512 pixels in size is shown, using simple tiling without orientation correction, edge matching or any image processing. Bright features correspond to SHG scattering at 400 nm, in the forward (transmitted) direction, of laser light at 800 nm in approximately 140 fs pulses. SHG contrast in the image derives from a complex distribution of nonlinear susceptibility in non-centro-symmetric fibrillar collagen structures of varying diameters as well as linear scattering at both the primary and secondary wavelengths. The cross-sectional area of the microfocus X-ray beam is shown by a solid white rectangle and the cross-sectional area of a typical scan is shown by an open white rectangle.