Confocal laser scanning microscopy

As seen in the figure the detector aperture obstructs the so called out-of-focus (or out-of-plane) light: fluorescent light not originating from the focal plane of the objective lens. Light rays from below the focal plane come to a focus before reaching the detector pinhole, and then they expand out so that most of the rays are physically blocked from reaching the detector by the pinhole. In the same way, light from above the focal plane is focused behind the detector pinhole, so that most of this light also hits the edges of the pinhole and is not detected. However, all the light from the focal plane (solid lines) is focused at the pinhole and passed to the detector. In this way, out-of-focus information from above and below the focal plane is greatly reduced, which results in sharper images compared to conventional microscopy techniques.