What is the nature of the sample observed by the phase contrast microscope?
The so-called phase-contrast microscope, as the name suggests, uses "phase contrast" for observation. It is mainly used for the observation of biological cells and unstained biological slices. In principle, it uses the interference in the electromagnetic wave properties of light. A beam of electromagnetic waves can be represented by a wave function, generally simply using sine and cosine functions, and y=Asin(ax+b). If I remember correctly, b should be the phase, and of course it may be y=Asin(a (x+b)), the details of b in (x+b)) are not very clear, you can check it yourself, you should have talked about it in high school mathematics. Now suppose a beam of light passes through a glass plate. When the light enters the glass plate, it will be partially reflected, and when it passes through the glass plate, it will be reflected on another interface. The two reflected lights will be superimposed, resulting in an interference effect. Because light has a wavelength, and when it "walks" in the glass plate, the thickness of the glass plate is not necessarily an integer multiple of the wavelength, and when light propagates in different media, due to the different refractive index of the medium, it may be on the interface There is a half-wave loss, which will cause the two reflected beams to have different phases anyway, that is, one of them can be expressed as y1=Asin(ax+b1) and the other as y2=Asin(ax+b2) , and the result of the interference is that the wave function of the light actually seen is the sum of the two, that is, y=y1+y2, and different phase differences b1-b2 will cause the amplitude A of the sum function to be different. This formula is used in high school It also exists in mathematics, so it will lead to different light intensities seen by the naked eye. The basic principle of the phase contrast microscope is similar to this. The phase of the reflected or transmitted light at different positions of the cells or slices is different, which will lead to different light intensities, and can be observed accordingly.
