Phase Contrast Microscopy

Phase contrast microscope has the resolving power similar to ordinary light microscope. However, it enables us to observe the cellular organelles in living cell. The working of this microscope is based on the principle of phase contrast.

To understand phase contrast microscopy you should know that whenever two light waves interfere with each other, the resultant light wave may have either greater or lesser amplitude depending on the phases of the light waves (Figure shown below).

It is a known fact that a light wave passing through a transparent object suffers a change in phase.

The living cells are heterogeneous in their cellular components having different thickness. Due to this difference, each component has different refractive index. Hence, when a light wave passes through the cell, a change in phase is produced due to differences of thickness and refractive indices of cellular components. The phase contrast microscope exaggerates the small difference between the phases and enables one to distinguish the adjacent structures.