it has been known for a long time that some optical devices can "magnify" objects. For example, concave mirror, who can magnify objects, is recorded in the Book of Mohism. As for when the convex lens was invented, it may not be verified. A convex lens-sometimes referred to as a "magnifying glass"-can focus sunlight and let you see the magnified object, because the convex lens can turn deflection of light. What you see through the convex lens is actually an illusion, strictly speaking, it is called a virtual image. When the light emitted by an object passes through a convex lens, the light will be deflected in a specific way. When we see those lights, or unconsciously think that they are still traveling along a straight route. As a result, objects will look bigger than before.
a single convex lens can magnify an object by dozens of times, which is far from enough for us to see the details of some objects clearly. In the 13th century, glasses for people with poor eyesight appeared-a kind of lens made of glass. With the disappearance of the darkness that has enveloped Europe for a thousand years, various new inventions have emerged, and microscope is one of them. At about the end of 16th century, Zhan Sen, a Dutch optician, and his son put several lenses into a cylinder, and found that the objects nearby were surprisingly large through the cylinder, which is the predecessor of the present microscope and telescope.
in 1665, British scientist Robert? 6? When Hooke observed the cork slices with his microscope, he was surprised to find that there was a "unit" structure in them. Hook called them "cells". However, Zhan Sen's compound microscope didn't really show its power, and their magnification was pitifully low. Dutch Anthony? 6? 1 feng? 6? The microscope made by Anthony Von Leeuwenhoek (1632-1723) opened people's eyes. Levin Hooke learned the technology of grinding glasses from childhood and was keen on making microscopes. The microscope he made is actually a convex lens, not a compound microscope. However, due to his exquisite skills, the magnification of the grinded single-chip microscope is nearly 3 times, which exceeds any previous microscope.
When Levin Hooke aimed his microscope at a drop of rain, he was surprised to find an amazing little world: countless microorganisms swimming in it. He reported this discovery to the Royal Society, which caused a sensation. People sometimes refer to Levin Hooke as "the father of the microscope", which is not correct strictly. Levin Hooke didn't invent the first compound microscope, but his achievement was to produce a high-quality convex lens.
in the next two centuries, the compound microscope was fully improved, for example, people invented a lens group that can eliminate chromatic aberration (when light with different wavelengths passes through the lens, they refract in slightly different directions, which leads to the decline of imaging quality) and other optical errors. Compared with the microscopes in the 19th century, the ordinary optical microscopes we use now are basically not improved. The reason is simple: the optical microscope has reached the limit of resolution.
if you just draw on paper, you can naturally "make" a microscope with any magnification. But the fluctuation of light will ruin your perfect invention. Even if the defect of lens shape is eliminated, no optical instrument can image perfectly. It took people a long time to discover that light diffracts when it passes through a microscope-in short, a point on an object is not a point when it is imaged, but a diffraction spot. If two diffraction spots are too close, you can't tell them apart. No matter how high the magnification of the microscope is, it won't help. For a microscope using visible light as light source, its resolution limit is .2 micron. Any structure smaller than .2 micron can't be identified.
one of the ways to improve the resolution of microscope is to try to reduce the wavelength of light, or to replace light with electron beam. According to de Broglie's theory of matter wave, the moving electron has fluctuation, and the faster the speed, the shorter its "wavelength". If the speed of electrons can be increased high enough and concentrated, it may be used to enlarge objects.
in p>1938, German engineers Max Knoll and Ernst Ruska manufactured the world's first transmission electron microscope (TEM). In 1952, British engineer Charles Oatley manufactured the first scanning electron microscope (SEM). Electron microscope is one of the most important inventions in the 2th century. Because the speed of electrons can be increased to a very high level, the resolution of the electron microscope can reach the nanometer level (1-9m). Many objects invisible to visible light, such as viruses, show their original forms under the electron microscope.
it may be an unconventional idea to replace light with electrons. But there is something even more surprising. In 1983, Gerd Binnig and Heinrich Rohrer, two scientists from the Zurich Laboratory of IBM Company, invented the so-called scanning tunneling microscope (STM). This kind of microscope is more radical than electron microscope, and it completely loses the concept of traditional microscope.
obviously, you can't "see" atoms directly. Because atoms are different from macro-matter, they are not smooth, round and round chopping balls, let alone reaching? 6? 1 The model used by Finch in painting. Scanning tunneling microscope works by the so-called "tunneling effect". If we abandon complex formulas and terminology, this working principle is actually easy to understand. Tunnel scanning microscope has no lens, it uses a probe. A voltage is applied between the probe and the object. If the probe is very close to the surface of the object-on the order of nanometers-the tunneling effect will come into play. Electrons will pass through the gap between the object and the probe, forming a weak current. If the distance between the probe and the object changes, the current will also change accordingly. In this way, we can know the shape of the surface of the object by measuring the current, and the resolution can reach the level of a single atom.
Because of this wonderful invention, Binnig and Rohrer won the Nobel Prize in Physics in 1986. This year, another person shared the Nobel Prize in Physics, that is Ruska, the inventor of the electron microscope.
It is said that hundreds of years ago, Levin Hooke regarded his technique of making microscopes as a secret. Today, the microscope-at least the optical microscope-has become a very common tool to let us know about this small world.