App note from Newport about laser microscopy. Link here
Optical microscopes have been instrumental in the study of the life sciences for centuries. Since the invention of the laser, many advanced bioimaging techniques using microscopy have been created with progress accelerating greatly in the last two decades. Limitations in optical penetration depth, due to the scattering of light, originally limited studies to thin samples and, by necessity, processes taking place outside of the organism (ex vivo). In recent years, in vivo techniques have been developed that can visualize within the living organism or cell and have led to greatly increased understanding of cell function. Any bioimaging technique requires generating a signal from each portion of the cell or organism through some method of contrast.