Three-dimensional (3D) backward and forward second harmonic generation (SHG) microscopy of biological tissues.

In this work we aim to show how it is possible to exploit the second harmonic generation (SHG) signal for producing multimodal microscopic images of biological tissues. SHG microscopy constitutes an important tool for high-resolution, high-contrast, three-dimensional studies of live cell and tissue architectures. The physical origins of SHG within these tissues are addressed and reported in a comprehensive image gallery. Although SHG is a coherent process, the multiple scattering of tissue samples determines the ability to acquire signal in both backward and forward direction. We discuss here some key elements related to the backward and forward SHG signal in terms of acquisition architecture and related microscopic imaging.