What are the differences between a phase contrast microscope and a regular microscope?
Phase contrast microscope is a special microscope that converts the optical path difference (i.e. phase difference) generated by light passing through transparent specimen details into light intensity difference.
When light passes through a relatively transparent specimen, there is no significant change in the wavelength (color) and amplitude (brightness) of the light. Therefore, when observing unstained specimens (such as living cells) under a regular optical microscope, their morphology and internal structure are often difficult to distinguish. However, due to the differences in refractive index and thickness of various parts of the cell, there will be differences in the optical path of direct and diffracted light when light passes through this type of specimen. As the optical path increases or decreases, the phase of accelerating or lagging light waves will change (resulting in phase difference). The phase difference of light cannot be felt by the naked eye, but a phase contrast microscope can use its special device - a circular aperture and a phase plate - to transform the phase difference of light into an amplitude difference (brightness difference) that can be detected by the human eye through the interference phenomenon of light, thereby making previously transparent objects exhibit significant brightness differences and enhancing contrast, This enables us to observe living cells and certain fine structures within cells that cannot be seen or clearly seen under ordinary optical and dark field microscopes.
The imaging principle of a phase contrast microscope: The optical source can only pass through a transparent ring of a circular aperture during microscopic examination, and after passing through a concentrator, it gathers into a beam of light. When this beam of light passes through the object being tested, it undergoes varying degrees of deviation (diffraction) due to the different optical paths of each part. Due to the fact that the image formed by the transparent ring happens to coincide with the conjugate surface on the phase plate and the focal plane behind the objective lens. Therefore, direct light that has not deviated passes through the conjugate surface, while diffracted light that has deviated passes through the compensating surface. Due to the different properties of the conjugate surface and compensation surface on the phase plate, they will respectively generate a certain phase difference and intensity reduction of the light passing through these two parts. The two sets of light will converge through the rear lens and travel on the same optical path, causing interference between direct and diffracted light, changing the phase difference into amplitude difference. In this way, during phase contrast microscope examination, the light from a colorless transparent body converts the phase difference that cannot be resolved by the human eye into the amplitude difference (light and dark difference) that can be resolved by the human eye.
