Photons
2024-5-5
Some key properties of photons
The propagation of light (in free space or in a waveguide) is actually the propagation of waves. The amplitude of the quantum mechanical field at a certain point at a certain time is the superposition of all possible paths of light. Superposition may interfere constructively or destructively, which is the basis of optical interference effects. It is difficult for pure particle images to be consistent with experimental observations. For example, in the traditional double-slit interference experiment, each particle will pass through one of the slits and is irrelevant to the other slit; but this cannot explain that only after one slit is blocked, The phenomenon that some particles can reach a certain position but cannot reach that position when both slits are open (destructive interference).
When light interacts with atoms or other particles, only energy that is an integral multiple of the photon energy h ν can be absorbed or released by the light field. This can be simply understood as only a certain number of photons can be absorbed or radiated. The interaction process occurs only if the interacting particles (e.g. atoms) are able to receive these energies, i.e. the energy level difference between their quantum mechanical energy levels corresponds to the photon energy, or is an integer multiple of the photon energy (see two-photon absorption). A pure wave picture treats these energy limits as resonance effects, but cannot explain the quantization of energy.
In sensitive photodetectors, energy quantization is particularly obvious and photon counting can be performed, that is, single-photon absorption effects can be detected. This has applications in many fields of science and technology.
The rest mass of a photon is 0, so it cannot be slowed down or stopped. The existence of the so-called slow light phenomenon is caused by the strong interaction between the electromagnetic field and matter, so this phenomenon only exists in the medium. At this time, it is not just electromagnetic field excitation, and pure photon images cannot give a very reasonable explanation.
Due to the Poisson property of photons, multiple photons tend to excite the same pattern of radiation fields. For example, it can be found during stimulated emission of radiation (important in lasers), and can also be seen in the energy spectrum after thermally stimulated radiation (blackbody radiation).
Photons can exist in an entangled state, that is, some properties (for example, polarization) of different photons are coherent, although these properties only have specific values when measured. Since the measurement of different photons can occur at different locations, this would seem to mean that superluminal transmission of information is possible (the Einstein-Podolsky-Rosen paradox), but in fact it does not happen.
Quantum theory can be applied not only to visible light, but also to any electromagnetic wave phenomenon. But in radio frequency technology, quantum effects are not as important as in optical and laser technology. This is because the photon energy of radio waves is very small compared to its thermal energy at room temperature, while the opposite is true in optical phenomena.
In laser physics, a common phenomenon is that photons propagate in media, such as transparent crystals or glass, and laser gain media. Strictly speaking, it is not appropriate to call it a photon at this time, because the electromagnetic wave will interact with the medium, so what is propagated is a quasi-particle, sometimes called a polariton, which is similar to the product of the coupling between the excited state of the electromagnetic field and the polarized medium.
The propagation of light (in free space or in a waveguide) is actually the propagation of waves. The amplitude of the quantum mechanical field at a certain point at a certain time is the superposition of all possible paths of light. Superposition may interfere constructively or destructively, which is the basis of optical interference effects. It is difficult for pure particle images to be consistent with experimental observations. For example, in the traditional double-slit interference experiment, each particle will pass through one of the slits and is irrelevant to the other slit; but this cannot explain that only after one slit is blocked, The phenomenon that some particles can reach a certain position but cannot reach that position when both slits are open (destructive interference).
When light interacts with atoms or other particles, only energy that is an integral multiple of the photon energy h ν can be absorbed or released by the light field. This can be simply understood as only a certain number of photons can be absorbed or radiated. The interaction process occurs only if the interacting particles (e.g. atoms) are able to receive these energies, i.e. the energy level difference between their quantum mechanical energy levels corresponds to the photon energy, or is an integer multiple of the photon energy (see two-photon absorption). A pure wave picture treats these energy limits as resonance effects, but cannot explain the quantization of energy.
In sensitive photodetectors, energy quantization is particularly obvious and photon counting can be performed, that is, single-photon absorption effects can be detected. This has applications in many fields of science and technology.
The rest mass of a photon is 0, so it cannot be slowed down or stopped. The existence of the so-called slow light phenomenon is caused by the strong interaction between the electromagnetic field and matter, so this phenomenon only exists in the medium. At this time, it is not just electromagnetic field excitation, and pure photon images cannot give a very reasonable explanation.
Due to the Poisson property of photons, multiple photons tend to excite the same pattern of radiation fields. For example, it can be found during stimulated emission of radiation (important in lasers), and can also be seen in the energy spectrum after thermally stimulated radiation (blackbody radiation).
Photons can exist in an entangled state, that is, some properties (for example, polarization) of different photons are coherent, although these properties only have specific values when measured. Since the measurement of different photons can occur at different locations, this would seem to mean that superluminal transmission of information is possible (the Einstein-Podolsky-Rosen paradox), but in fact it does not happen.
Quantum theory can be applied not only to visible light, but also to any electromagnetic wave phenomenon. But in radio frequency technology, quantum effects are not as important as in optical and laser technology. This is because the photon energy of radio waves is very small compared to its thermal energy at room temperature, while the opposite is true in optical phenomena.
In laser physics, a common phenomenon is that photons propagate in media, such as transparent crystals or glass, and laser gain media. Strictly speaking, it is not appropriate to call it a photon at this time, because the electromagnetic wave will interact with the medium, so what is propagated is a quasi-particle, sometimes called a polariton, which is similar to the product of the coupling between the excited state of the electromagnetic field and the polarized medium.
