What is the resolution limit of an optical microscope?
SKYLABS published in the previous "Can we use optical microscope to observe atoms?" "The article actually mentioned that we cannot use optical microscopes to observe objects at the atomic level. Today in this issue, let me introduce to you what is the resolution limit of an optical microscope?
In fact, the problem of the resolution limit of the optical microscope was answered by the German physicist Abbe in 1873. Abbe discovered the limit formula of optical microscope resolution through calculation and derivation. The limit calculated by this formula is also called Abbe limit.
The eyepieces and objective lenses used in optical microscopes are actually convex lenses. Airy disks are generated when light passes through the convex lenses. A point we see through the microscope is actually a spot of light. If the two points that need to be observed are relatively far apart, we can still distinguish them. But if these two points are very, very close, so close that the two Airy disks they generate overlap, then we can't tell whether it is two points, and we can only see a blur a bunch of. Therefore, the size of the Airy disk actually determines the resolution limit of the microscope. Due to the limited space, Mr. Tianzong put aside the derivation process here and gave a formula for the resolution of an optical microscope, as follows:
δ=0.61λ/(nSinα)
δ: Resolution λ: Wavelength n: Refractive Index α: Aperture Angle
After simple conversion, this formula is approximately equal to 1/2 λ, that is to say, 1/2 wavelength is actually the limit of optical microscope resolution, and later generations defined it as "Abbe's limit".
The wavelength of violet light with the shortest wavelength in visible light is about 400 nanometers, and the Abbe limit is about 200 nanometers. That is to say, if the distance between two points is less than 200 nanometers, the two points cannot be distinguished by optical microscope, which is the resolution limit of optical microscope.
