Which industries utilize optical microscopes the most?
The optical microscope is an ancient and young scientific tool. It has a history of 300 years since its birth. The optical microscope is widely used, such as in biology, chemistry, physics, astronomy, etc. in some scientific research work All without a microscope.
At present, it has almost become the image endorsement of science and technology. You only need to see its figure frequently appearing in the media reports about science and technology to see that this statement is true.
In biology, the laboratory is inseparable from this kind of experimental equipment, which can help learners to study the unknown world; to understand the world.
Hospitals are the largest application places for microscopes, which are mainly used to check information such as changes in patient’s body fluids, germs invading the human body, changes in cell tissue structure, etc., and provide doctors with reference and verification methods for formulating treatment plans. In microsurgery, the microscope is the only tool for doctors; in agriculture, breeding, pest control and other work cannot do without the help of the microscope; in industrial production, the processing inspection and assembly adjustment of fine parts, and the research of material properties are all possible with the microscope. A place to show their talents; criminal investigators often rely on microscopes to analyze various microscopic crimes, as an important means to determine the real murderer; environmental protection departments also need microscopes to detect various solid pollutants; geological and mining engineers and cultural relics archaeologists use The clues found by the microscope can judge the deep-buried mineral deposits or infer the dusty historical truth; even people's daily life cannot do without the microscope, such as the beauty and hairdressing industry, which can use the microscope to detect skin and hair quality. Can get the best results. It can be seen how closely the microscope is integrated with people's production and life.
According to different application purposes, microscopes can be roughly classified into four categories: biological microscopes, metallographic microscopes, stereo microscopes, and polarizing microscopes. As the name implies, biological microscopes are mainly used in biomedicine, and the observation objects are mostly transparent or translucent micro bodies; metallographic microscopes are mainly used to observe the surface of opaque objects, such as the metallographic structure and surface defects of materials; While the object is magnified and imaged, the orientation of the object and the image relative to the human eye is also consistent, and there is a sense of depth, which is in line with people's conventional visual habits; Polarizing microscopes use the transmission or reflection characteristics of different materials for polarized light to distinguish different micro objects Component. In addition, some special types can also be subdivided, such as an inverted biological microscope or a culture microscope, which is mainly used to observe the culture through the bottom of the culture vessel; a fluorescence microscope uses certain substances to absorb specific shorter wavelength light The characteristics of emitting specific longer wavelength light to discover the existence of these substances and judge their content; the comparison microscope can form juxtaposed or superimposed images of two objects in the same field of view, so as to compare the similarities and differences of the two objects.
Traditional optical microscopes are mainly composed of optical systems and their supporting mechanical structures. The optical systems include objective lenses, eyepieces and condenser lenses, all of which are complicated magnifying glasses made of various optical glasses. The objective lens enlarges the image of the specimen, and its magnification M object is determined by the following formula: M object = Δ∕f' object , where f' object is the focal length of the objective lens, and Δ can be understood as the distance between the objective lens and the eyepiece. The eyepiece magnifies the image formed by the objective lens again, and forms a virtual image at 250mm in front of the human eye for observation. This is the most comfortable observation position for most people. The magnification of the eyepiece M eye=250/f' eye, f' eye is the eyepiece focal length. The total magnification of the microscope is the product of the objective lens and the eyepiece, that is, M=M object*M eye=Δ*250/f' eye *f; object. It can be seen that reducing the focal length of the objective lens and the eyepiece will increase the total magnification, which is the key to seeing bacteria and other microorganisms with a microscope, and it is also the difference between it and ordinary magnifying glasses.
So, is it conceivable to reduce the f' object f' mesh without limit, so as to increase the magnification, so that we can see more subtle objects? The answer is no! This is because the light used for imaging is essentially a kind of electromagnetic wave, so diffraction and interference phenomena will inevitably occur during the propagation process, just like the ripples on the water surface that can be seen in daily life can go around when encountering obstacles, and two columns of water waves can strengthen each other when they meet Or weaken the same. When the light wave emitted from a point-shaped luminous object enters the objective lens, the frame of the objective lens hinders the propagation of light, resulting in diffraction and interference. There is a series of light rings with weak and gradually weakening intensity. We call the central bright spot as the Airy disk. When two light-emitting points are close to a certain distance, the two light spots will overlap until they cannot be confirmed as two light spots. Rayleigh proposed a judgment standard, thinking that when the distance between the centers of the two light spots is equal to the radius of the Airy disk, the two light spots can be distinguished. After calculation, the distance between the two light-emitting points at this time is e=0.61 入/n.sinA=0.61 I/N.A, where I is the wavelength of light, the wavelength of light that can be received by the human eye is about 0.4-0.7um, and n is the refractive index of the medium where the light-emitting point is located, such as in air, n≈1, in water , n≈1.33, and A is half of the opening angle of the light-emitting point to the frame of the objective lens, and N.A is called the numerical aperture of the objective lens. It can be seen from the above formula that the distance between two points that can be distinguished by the objective lens is limited by the wavelength of light and the numerical aperture. Since the wavelength of the most acute vision of the human eye is about 0.5um, and the angle A cannot exceed 90 degrees, sinA is always less than 1. The maximum refractive index of the available light-transmitting medium is about 1.5, so the e value is always greater than 0.2um, which is the minimum limit distance that the optical microscope can distinguish. Magnify the image through a microscope, if you want to magnify the object point distance e that can be resolved by the objective lens with a certain N.A value enough to be resolved by the human eye, you need M.e ≥ 0.15mm, where 0.15mm is the experimental value of the human eye The minimum distance between two micro-objects that can be distinguished at 250mm in front of the eyes, so M≥ (0.15∕0.61 in) N.A≈500N.A, in order to make the observation not too laborious, it is enough to double the M, that is, 500N. A≤M≤1000N.A is a reasonable selection range of the total magnification of the microscope. No matter how large the total magnification is, it is meaningless, because the numerical aperture of the objective lens has limited the minimum resolvable distance, and it is impossible to distinguish more by increasing the magnification. Small objects are detailed.
Imaging contrast is another key issue of optical microscopes. The so-called contrast refers to the black-and-white contrast or color difference between adjacent parts on the image surface. It is difficult for the human eye to judge the brightness difference below 0.02. is slightly more sensitive. For some microscope observation objects, such as biological specimens, the brightness difference between the details is very small, and the design and manufacturing errors of the microscope optical system further reduce the imaging contrast and make it difficult to distinguish. At this time, the details of the object cannot be seen clearly, not because the total magnification is too low , nor is the numerical aperture of the objective lens too small, but because the contrast of the image plane is too low.
Over the years, people have worked hard to improve the resolution and imaging contrast of the microscope. With the continuous advancement of computer technology and tools, the theory and methods of optical design are also continuously improved. Coupled with the improvement of raw material performance, process and The continuous improvement of detection methods and the innovation of observation methods have made the imaging quality of the optical microscope close to the perfection of the diffraction limit. People will use specimen staining, dark field, phase contrast, fluorescence, interference, polarization and other observation techniques to make the optical microscope It can adapt to the research of all kinds of specimens. Although electron microscopes, ultrasonic microscopes and other magnifying imaging instruments have come out successively in recent years, and have superior performance in some aspects, they are still not available in terms of cheapness, convenience, intuition, and especially suitable for research on living organisms. Rival to the light microscope, which still holds its ground firmly. On the other hand, combined with laser, computer, new material technology and information technology, the ancient optical microscope is rejuvenating and showing vigorous vitality. Digital microscope, laser confocal scanning microscope, near-field scanning microscope, two-photon microscope and There are various new functions or instruments that can adapt to various new environmental conditions emerge in an endless stream, which further expands the application field of optical microscopes. How exciting are the microscopic pictures of rock formations uploaded from the Mars rovers! We can fully believe that the optical microscope will benefit mankind with an updated attitude.
