Phasenkontrastmikroskopieansatz

Phasenkontrastmikroskopieansatz, also known as phase contrast microscopy, is a technique used to visualize transparent specimens that are difficult to see with conventional bright-field microscopy. It works by exploiting the differences in refractive index between the specimen and its surrounding medium. When light passes through a specimen with a different refractive index, it is slowed down and undergoes a phase shift. This phase shift is normally undetectable by the human eye. The phase contrast microscope converts these invisible phase shifts into amplitude differences, which appear as variations in brightness or darkness in the image. This allows unstained biological samples, such as living cells and microorganisms, to be observed with remarkable clarity.

The key components of a phase contrast microscope are a condenser annulus and a phase plate. The condenser annulus is a diaphragm with a ring-shaped opening that allows light to pass through, creating a hollow cone of illumination. This light then passes through the specimen. The phase plate, located in the objective lens, contains a ring that corresponds to the condenser annulus. This ring alters the phase of the light that has passed through the specimen, while the rest of the light (the undiffracted light) is either advanced or retarded. This specific phase manipulation, combined with destructive or constructive interference, leads to the observed contrast in the final image. Phasenkontrastmikroskopieansatz is particularly valuable in cell biology for observing cellular structures, cell division, and dynamic cellular processes in living cells without the need for staining, which can often kill or alter the cells.