The difference between optical and electron microscopes
1, Different light sources
Optical microscopes use visible light as the light source, while electron microscopes use electron beams as the light source.
2, Different imaging principles
Optical microscopes use geometric optical imaging principles for imaging, while electron microscopes use high-energy electron beams to bombard the surface of samples, exciting various physical signals on the sample surface, and then using different signal detectors to receive the physical signals and convert them into image information.
3, Different resolutions
Due to the interference and diffraction of light, the resolution of optical microscopes can only be limited to between 0.2-0.5um. Electron microscopy, which uses an electron beam as a light source, has a resolution of 1-3 nm. Therefore, tissue observation under optical microscopy belongs to micrometer level analysis, while tissue observation under electron microscopy belongs to nanometer level analysis.
4, Different depth of field
The depth of field of a general optical microscope is between 2-3um, so it has extremely high requirements for the surface smoothness of the sample, making the sample preparation process relatively complex. The depth of field of an electron microscope can reach several millimeters, so there are no geometric requirements for the smoothness of the sample surface, and sample preparation is relatively simple. Some samples almost do not require sample preparation, although the stereomicroscope also has a relatively large depth of field.
In terms of applications in biology, the resolution of optical microscopes is far inferior to that of electron microscopes, because the resolution of optical microscopes is limited by the diffraction limit, so its resolution cannot be less than half of the wavelength of the incident light. That is to say, if 400nm incident light is used, the observed object cannot be smaller than 200nm. However, due to its real-time and dynamic observation capabilities, its position in biology is unparalleled, and it is impossible to do without optical microscopes such as fluorescence microscopy and confocal microscopy in the field of biology. Due to the use of electron beams for scanning imaging, electron microscopes can easily achieve nanometer level resolution, which is irreplaceable for high-resolution imaging applications.
In terms of application in metallographic analysis, the magnification of electron microscopes far exceeds that of optical microscopes. The maximum magnification of modern electron microscopes has exceeded 3 million times, while the maximum magnification of optical microscopes is about 2000 times. Therefore, electron microscopes can directly observe the atoms of certain heavy metals and the neatly arranged atomic lattice in crystals.
